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Authentication-Results: mta4002.groups.mail.bf1.yahoo.com [email protected]; header.s�hoe; dkim=permerror (bad sig) Date: 07 Jun 2019 03:16:15 +0000 Subject: Compass Web Site.Warning Messages From: [email protected] A few months back I received some emails from people complaining that they were having problems accessing the Compass web site. When they went to the Compass web site, they would get a message saying the web site was unsafe and warning them not to enter. When I tested the web site, I didn't get the message. I tested it in several browsers and didn't see a problem, so I assumed it was an erroneous message. A few days ago I received notification from Google that they want all web sites to use SSL encryption so people can connect to web sites using HTTPS. They warned that web sites not using SSL/HTTPS might be blocked. That made me realize that Google had probably rolled out the feature early in some parts of the country and that was causing the warning. The Compass web site uses CloudFlare https://www.cloudflare.com/, which makes it easy to switch on SLL and allow HTTPS encryption. The Compass web site has been switched over so traffic can now use SSL encryption. I've also configured it to force SSL encryption even when the browser doesn't request it. The Compass web site was never really unsafe and now it is even safer. If you have been avoiding the Compass web site because of the warning messages, they should now be gone now. I apologize for any inconvenience this may have caused. If you notice any problems with the change to SSL, please let me know. Larry Fish A few months back I received some emails from people complaining that they were having problems accessing the Compass web site. When they went to the Compass web site, they would get a message saying the web site was unsafe and warning them not to enter.When I tested the web site, I didn't get the message. I tested it in several browsers and didn't see a problem, so I assumed it was an erroneous message.A few days ago I received notification from Google that they want all web sites to use SSL encryption so people can connect to web sites using HTTPS. They warned that web sites not using SSL/HTTPS might be blocked. That made me realize that Google had probably rolled out the feature early in some parts of the country and that was causing the warning.The Compass web site uses CloudFlare, which makes it easy to switch on SLL and allow HTTPS encryption. The Compass web site has been switched over so traffic can now use SSL encryption. I've also configured it to force SSL encryption even when the browser doesn't request it.The Compass web site was never really unsafe and now it is even safer. If you have been avoiding the Compass web site because of the warning messages, they should now be gone now. I apologize for any inconvenience this may have caused. If you notice any problems with the change to SSL, please let me know.Larry Fish
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Date: Tue, 11 Jun 2019 17:14:04 +0200
Subject: RE: [compass-users] Compass Web Site.Warning Messages
From: "Paul De Bie"
Thanks for the information Larry.
Personally, I feel that it is stupid of Google trying to push everything and everyone to using https.
It gives people a false feeling of security. They think nothing can happen to them because it is an encrypted site. But there is nothing safe about a https site�?� apart from the connection itself.
Any https site can be just as infected with malware as a regular http site.
https://www.kaspersky.com/blog/https-does-not-mean-safe/20725/
Paul De Bie
http://www.scavalon.be
http://scavalon.blogspot.com
From: [email protected]
Sent: Friday, June 7, 2019 5:16 AM
Subject: [compass-users] Compass Web Site.Warning Messages
A few months back I received some emails from people complaining that they were having problems accessing the Compass web site. When they went to the Compass web site, they would get a message saying the web site was unsafe and warning them not to enter.
When I tested the web site, I didn't get the message. I tested it in several browsers and didn't see a problem, so I assumed it was an erroneous message.
A few days ago I received notification from Google that they want all web sites to use SSL encryption so people can connect to web sites using HTTPS. They warned that web sites not using SSL/HTTPS might be blocked.
That made me realize that Google had probably rolled out the feature early in some parts of the country and that was causing the warning.
The Compass web site uses CloudFlare, which makes it easy to switch on SLL and allow HTTPS encryption. The Compass web site has been switched over so traffic can now use SSL encryption. I've also configured it to force SSL encryption even when the browser doesn't request it.
The Compass web site was never really unsafe and now it is even safer. If you have been avoiding the Compass web site because of the warning messages, they should now be gone now.
I apologize for any inconvenience this may have caused. If you notice any problems with the change to SSL, please let me know.
Larry Fish
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Date: Tue, 11 Jun 2019 17:09:57 -0600
Subject: RE: [compass-users] Compass Web Site.Warning Messages
From: "Larry"
Paul,
I agree. I only did it because Google Chrome can give a warning message
saying the site is unsafe. Judging from the emails I've received, people get
pretty upset when they see it and it is hard to convince them the site
really is safe.
I've also noticed that since I did it, the number of people reaching the
site has dropped by about 20%. I'm not sure why. I haven't seen issues
getting to the site so hopefully it is just an anomaly. Maybe cavers are
just doing more caving as the weather has gotten warmer. (Or maybe if you
are in hot parts of the Southern Hemisphere, the weather getting cooler.)
Larry
_____
From: [email protected] [mailto:[email protected]]
Sent: Tuesday, June 11, 2019 9:14 AM
Subject: RE: [compass-users] Compass Web Site.Warning Messages
Thanks for the information Larry.
Personally, I feel that it is stupid of Google trying to push everything and
everyone to using https.
It gives people a false feeling of security. They think nothing can happen
to them because it is an encrypted site. But there is nothing safe about a
https site. apart from the connection itself.
Any https site can be just as infected with malware as a regular http site.
https://www.kaspersky.com/blog/https-does-not-mean-safe/20725/
Paul De Bie
http://www.scavalon.be
http://scavalon.blogspot.com
From: [email protected]
Sent: Friday, June 7, 2019 5:16 AM
Subject: [compass-users] Compass Web Site.Warning Messages
A few months back I received some emails from people complaining that they
were having problems accessing the Compass web site. When they went to the
Compass web site, they would get a message saying the web site was unsafe
and warning them not to enter.
When I tested the web site, I didn't get the message. I tested it in several
browsers and didn't see a problem, so I assumed it was an erroneous message.
A few days ago I received notification from Google that they want all web
sites to use SSL encryption so people can connect to web sites using HTTPS.
They warned that web sites not using SSL/HTTPS might be blocked.
That made me realize that Google had probably rolled out the feature early
in some parts of the country and that was causing the warning.
The Compass web site uses CloudFlare, which
makes it easy to switch on SLL and allow HTTPS encryption. The Compass web
site has been switched over so traffic can now use SSL encryption.. I've
also configured it to force SSL encryption even when the browser doesn't
request it.
The Compass web site was never really unsafe and now it is even safer. If
you have been avoiding the Compass web site because of the warning messages,
they should now be gone now.
I apologize for any inconvenience this may have caused. If you notice any
problems with the change to SSL, please let me know.
Larry Fish
v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
st1\:*{behavior:url(#default#ieooui) }
Authentication-Results: mta4002.groups.mail.bf1.yahoo.com [email protected]; header.s�hoe; dkim=permerror (bad sig) Date: 12 Jun 2019 02:29:29 +0000 Subject: Compass/Inkscape workshop at Convention From: [email protected] I just got this message today. There is going to a half-day workshop at the NSS Convention this summer focusing on using Inkscape and Compass to draw maps. The convention will be held June 17th through the 21st at Cookeville, Tennessee. Here is the convention web page: http://nss2019.subworks.com/ http://nss2019.subworks.com/ Here is the email I received: Hello, Ray Keeler sent the message below to the Survey and Cartography Section???s Facebook page and I'm forwarding it to the SCAS email list in case you didn't see it on Facebook. Bob Hoke -------------------------------------------------------------- There is an Inkscape workshop drawing cave maps at the 2019 NSS Convention on Monday morning. The workshop will be 9 am to 12 noon. Room 31. I just looked at the 2019 schedule and the workshop description is not in the schedule. Inkscape is a free and open-source vector graphics editor and is excellent for making cave maps. There are similarities to Adobe Illustrator tools. Compass (Larry Fish, $25 lifetime subscription, very popular) processes cave survey data that can be exported into Inkscape format. This is a hands on workshop on how get survey data into a finished map form. Participants are encouraged to bring laptops. We will go from Exporting the Compass data to Inkscape and drawing a sample cave map to creating the printable map. I will have a flash drive for downloading files with a sample cave, survey data and survey sketches. Bring writing materials for notes. This will be fun. Inkscape has become so popular that Illustrator now has the capability to import the Inkscape formats. My apologies for not getting the Inkscape workshop description in to the schedule in time (submitted April 22nd) but if you are at the Convention please feel welcome. Our goal is to get maps out ... the results of the surveyors' efforts. thanks, Ray Keeler [email protected] 623-523-1760 mY0�1_ �1_ P I just got this message today. There is going to a half-day workshop at the NSS Convention this summer focusing on using Inkscape and Compass to draw maps. The convention will be held June 17th through the 21st at Cookeville, Tennessee. Here is the convention web page:http://nss2019.subworks.com/Here is the email I received:Hello,Ray Keeler sent the message below to the Survey and Cartography Section???s Facebook page and I'm forwarding it to the SCAS email list in case you didn't see it on Facebook.Bob Hoke--------------------------------------------------------------There is an Inkscape workshop drawing cave maps at the 2019 NSS Convention on Monday morning. The workshop will be 9 am to 12 noon. Room 31. I just looked at the 2019 schedule and the workshop description is not in the schedule.Inkscape is a free and open-source vector graphics editor and is excellent for making cave maps. There are similarities to Adobe Illustrator tools. Compass (Larry Fish, $25 lifetime subscription, very popular) processes cave survey data that can be exported into Inkscape format. This is a hands on workshop on how get survey data into a finished map form. Participants are encouraged to bring laptops. We will go from Exporting the Compass data to Inkscape and drawing a sample cave map to creating the printable map. I will have a flash drive for downloading files with a sample cave, survey data and survey sketches. Bring writing materials for notes. This will be fun.Inkscape has become so popular that Illustrator now has the capability to import the Inkscape formats.My apologies for not getting the Inkscape workshop description in to the schedule in time (submitted April 22nd) but if you are at the Convention please feel welcome. Our goal is to get maps out ... the results of the surveyors' efforts.thanks,Ray [email protected]
Authentication-Results: mta4002.groups.mail.bf1.yahoo.com; dkim=pass (ok) [email protected] header.s�048; spf=pass [email protected]; dmarc=pass(p=reject sp=NULL dis=none) header.from=verizon.net; Date: Thu, 18 Jul 2019 18:38:26 -0500 Subject: plot color by excluded for length From: Dwight Livingston Larry & everyone I'd like to see which shots are included and excluded for length in a plot, say by color coding. Any way to do that? Thanks Dwight
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Authentication-Results: mta4002.groups.mail.bf1.yahoo.com; dkim=pass (ok) [email protected] header.s�048; spf=pass [email protected]; dmarc=pass(p=reject sp=NULL dis=none) header.from=verizon.net; Date: Sat, 20 Jul 2019 15:02:23 -0500 Subject: Re: [compass-users] plot color by excluded for length From: Dwight Livingston Thanks, Larry. On 7/19/2019 2:02 AM, 'Paul De Bie' [email protected] [compass-users] wrote: Hi, In the menu: Display, Show, Show length excluded shots Paul De Bie http://www.scavalon.be http://scavalon.blogspot.com -----Original Message----- From: [email protected] Sent: Friday, July 19, 2019 1:38 AM To: Larry Fish Subject: [compass-users] plot color by excluded for length Larry & everyone I'd like to see which shots are included and excluded for length in a plot, say by color coding. Any way to do that? Thanks Dwight ------------------------------------ Posted by: Dwight Livingston ------------------------------------ ------------------------------------ Yahoo Groups Links ------------------------------------------------------------------------ AVG logo This email has been checked for viruses by AVG antivirus software. www.avg.com
Authentication-Results: mta4001.groups.mail.ne1.yahoo.com; dkim=pass (ok) [email protected] header.s 190202a; spf=pass [email protected]; dmarc=pass(p=none sp=NULL dis=none) header.from=comcast.net; Date: Mon, 23 Sep 2019 12:13:42 -0500 Subject: Magnetic Anomalies From: David Gerboth Larry, I read the information given about Magnetic Anomalies when surveying in caves. Would the techniques apply to a cave that lies directly under a major power line? We get wild readings when we try to use a compass. - Dave
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Date: Mon, 23 Sep 2019 16:55:41 -0600
Subject: RE: [compass-users] Magnetic Anomalies
From: "Larry"
Hi Dave,
Thanks for your email. I'm not sure whether it would work or not. It would
depend on whether the magnetic field from the power-lines was consistent.
Here are some thoughts off the top of my head on the subject:
The power-line voltage is alternating at 60 times per second. That would
mean the magnetic field would be reversing 60 times per second. In other
words, the magnetic field will oriented to magnetic-north for 1/120 of a
second and magnetic-south for 1/120 of a second.
A compass cannot respond 60 times per second so it would tend to average out
the magnetic field. I would think the most you would see from the power
lines is a slight vibration of the needle. So, in theory, the inertia of the
needle should average out the reading and the net magnetic field would be
zero. In other words, the flip between north and south poles should cancel
out the magnetic field.
However, since you are seeing distortions, there obviously must be some
residual magnetic field from the power lines. Alternating current
electricity produces all kinds of complicated effects that aren't easy to
quantify. For example, the power lines can induce fields in nearby objects
or even magnetic rocks in the ground that could last longer than 1/60 of a
second.
The main thing is whether the magnetic fields are consistent. If the fields
don't change over time, then you should be able to use the concepts from the
article to correct the compass reading in the cave. If they fluctuate over
time, then the technique wouldn't be useful.
I would suggest testing the consistency of the anomaly in the cave. To do
this, you would go to a spot in the cave where the distortion is at a
maximum and set the compass in a place where it cannot move. Then you would
watch the needle over time and see if the compass reading changes. If it
changes rapidly, it would be hard to use the technique. If it changes slowly
or not at all, then you can use the technique.
Since the magnetic correct relies on taking fore and back sights, the key
question would be "can you survey a front and back sight before the readings
change?" If the readings are changing slowly enough, you should be able to
take a fore and back sight before it changes.
For example, if the readings are changing by one degree per minute, it is
probably too fast to do front and back sites. However, if it is changing at
one degree every ten minutes, you could probably get the readings needed to
cancel out magnetic anomalies. If they are changing at one degree per hour,
you shouldn't have any problem at all.
Even if it was changing at one degree per minute, you could use two
compasses, one for the fore sight and one for the back sight. However, you
have to make sure that both compasses are calibrated so you they both get
identical readings. Otherwise, you won't be able to tell if you are
cancelling out magnetic distortion or just adding in the relative error
between the two compasses.
Another thought that just occurred to me is that they now sometimes transmit
power using DC current instead of AC. If this is the case, the magnetic
field should be consistent in direction and would only vary intensity based
on the amount of current the lines are carrying. In that case, the anomaly
should be fairly consistent, although you'd still want to do the test in the
cave to see how much it changes over time.
Let me know if you have any thoughts or questions.
Larry Fish
_____
From: [email protected] [mailto:[email protected]]
Sent: Monday, September 23, 2019 11:14 AM
Subject: [compass-users] Magnetic Anomalies
Larry,
I read the information given about Magnetic Anomalies when surveying in
caves. Would the techniques apply to a cave that lies directly under a
major power line? We get wild readings when we try to use a compass.
- Dave
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Date: Mon, 23 Sep 2019 18:11:49 -0500
Subject: Re: [compass-users] Magnetic Anomalies
From: David Gerboth
Larry,
Thanks for the tips. I ran into the same problem in a sandstone mine
years ago, which I suspect had a small power line overhead and I was
getting up to 10 degree errors on the compass. After reading the
Anomalies report I remember the back sights did not agree with the front
sights. Not knowing the tips I just got, I gave up on that survey. I
will see how it works with this cave.
- Dave
On 9/23/2019 5:55 PM, 'Larry' [email protected] [compass-users] wrote:
Hi Dave,
Thanks for your email. I'm not sure whether it would work or not. It
would depend on whether the magnetic field from the power-lines was
consistent. Here are some thoughts off the top of my head on the subject:
The power-line voltage is alternating at 60 times per second. That
would mean the magnetic field would be reversing 60 times per second.
In other words, the magnetic field will oriented to magnetic-north for
1/120 of a second and magnetic-south for 1/120 of a second.
A compass cannot respond 60 times per second so it would tend to
average out the magnetic field. I would think the most you would see
from the power lines is a slight vibration of the needle. So, in
theory, the inertia of the needle should average out the reading and
the net magnetic field would be zero. In other words, the flip between
north and south poles should cancel out the magnetic field.
However, since you are seeing distortions, there obviously must be
some residual magnetic field from the power lines. Alternating current
electricity produces all kinds of complicated effects that aren't easy
to quantify. For example, the power lines can induce fields in nearby
objects or even magnetic rocks in the ground that could last longer
than 1/60 of a second.
The main thing is whether the magnetic fields are consistent. If the
fields don't change over time, then you should be able to use the
concepts from the article to correct the compass reading in the cave.
If they fluctuate over time, then the technique wouldn't be useful.
I would suggest testing the consistency of the anomaly in the cave. To
do this, you would go to a spot in the cave where the distortion is at
a maximum and set the compass in a place where it cannot move. Then
you would watch the needle over time and see if the compass reading
changes. If it changes rapidly, it would be hard to use the technique.
If it changes slowly or not at all, then you can use the technique.
Since the magnetic correct relies on taking fore and back sights, the
key question would be "can you survey a front and back sight before
the readings change?" If the readings are changing slowly enough, you
should be able to take a fore and back sight before it changes.
For example, if the readings are changing by one degree per minute, it
is probably too fast to do front and back sites. However, if it is
changing at one degree every ten minutes, you could probably get the
readings needed to cancel out magnetic anomalies. If they are changing
at one degree per hour, you shouldn't have any problem at all.
Even if it was changing at one degree per minute, you could use two
compasses, one for the fore sight and one for the back sight. However,
you have to make sure that both compasses are calibrated so you they
both get identical readings. Otherwise, you won't be able to tell if
you are cancelling out magnetic distortion or just adding in the
relative error between the two compasses.
Another thought that just occurred to me is that they now sometimes
transmit power using DC current instead of AC. If this is the case,
the magnetic field should be consistent in direction and would only
vary intensity based on the amount of current the lines are carrying.
In that case, the anomaly should be fairly consistent, although you'd
still want to do the test in the cave to see how much it changes over
time.
Let me know if you have any thoughts or questions.
Larry Fish
------------------------------------------------------------------------
*From:*[email protected]
[mailto:[email protected]]
*Sent:* Monday, September 23, 2019 11:14 AM
*To:* Compass-Users
*Subject:* [compass-users] Magnetic Anomalies
Larry,
I read the information given about Magnetic Anomalies when surveying in
caves. Would the techniques apply to a cave that lies directly under a
major power line? We get wild readings when we try to use a compass.
- Dave
Larry,
Thanks for the tips. I ran into the
same problem in a sandstone mine years ago, which I suspect had a
small power line overhead and I was getting up to 10 degree errors
on the compass. After reading the Anomalies report I remember the
back sights did not agree with the front sights. Not knowing the
tips I just got, I gave up on that survey. I will see how it works
with this cave.
- Dave
On 9/23/2019 5:55 PM, 'Larry'
[email protected] [compass-users] wrote:
�
Hi Dave,
Thanks
for your email. I'm not sure whether it would
work or not. It would depend on whether the magnetic
field from the power-lines
was consistent. Here are some thoughts off the top
of my head on the subject:
The
power-line voltage is alternating at 60 times per
second. That would mean the magnetic field would be
reversing 60 times per
second. In other words, the magnetic field will
oriented to magnetic-north for
1/120 of a second and magnetic-south for 1/120 of a
second.
A
compass cannot respond 60 times per second so it
would
tend to average out the magnetic field. I would
think the most you would see
from the power lines is a slight vibration of the
needle. So, in theory, the
inertia of the needle should average out the reading
and the net magnetic field
would be zero. In other words, the flip between
north and south poles should cancel
out the magnetic field.
However,
since you are seeing distortions, there obviously
must be some residual magnetic field from the power
lines. Alternating current
electricity produces all kinds of complicated
effects that aren't easy to
quantify. For example, the power lines can induce
fields in nearby objects or
even magnetic rocks in the ground that could last
longer than 1/60 of a second.
The main thing is whether the magnetic
fields are consistent. If the fields
don't change over time, then you should be able to
use the concepts from
the article to correct the compass reading in the
cave. If they fluctuate over
time, then the technique wouldn't be useful.
I would suggest testing the consistency of
the anomaly in the cave. To
do this, you would go to a spot in the cave where
the distortion is at a maximum
and set the compass in a place where it cannot move.
Then you would watch the
needle over time and see if the compass reading
changes. If it changes rapidly,
it would be hard to use the technique. If it changes
slowly or not at all, then
you can use the technique.
Since the magnetic correct relies on taking
fore and back sights, the
key question would be "can you survey a front and
back sight before the
readings change?" If the readings are changing
slowly enough, you should
be able to take a fore and back sight before it
changes.
For example, if the readings are changing
by one degree per minute, it
is probably too fast to do front and back sites.
However, if it is changing at
one degree every ten minutes, you could probably get
the readings needed to
cancel out magnetic anomalies. If they are changing
at one degree per hour, you
shouldn't have any problem at all.
Even if it was changing at one degree per
minute, you could use two
compasses, one for the fore sight and one for the
back sight. However, you have
to make sure that both compasses are calibrated so
you they both get identical
readings. Otherwise, you won't be able to tell if
you are cancelling out
magnetic distortion or just adding in the relative
error between the two compasses.
Another thought that just occurred to me is
that they now sometimes
transmit power using DC current instead of AC. If
this is the case, the
magnetic field should be consistent in direction and
would only vary intensity
based on the amount of current the lines are
carrying. In that case, the
anomaly should be fairly consistent, although you'd
still want to do the
test in the cave to see how much it changes over
time.
Let me know if you have any thoughts or
questions.
Larry Fish
�
�
From: [email protected]
[mailto:[email protected]]
Sent:
Monday, September 23, 2019
11:14 AM
To:
Compass-Users
Subject:
[compass-users] Magnetic
Anomalies
�
�
Larry,
I read the information given about Magnetic
Anomalies when surveying in
caves. Would the techniques apply to a cave
that lies directly under a
major power line? We get wild readings when we
try to use a compass.
- Dave
Authentication-Results: mta4000.groups.mail.ne1.yahoo.com; dkim=pass (ok) [email protected] header.s 161025; spf=pass [email protected]; dmarc=pass(p=none sp=quarantine dis=none) header.from=gmail.com; Date: Mon, 23 Sep 2019 19:19:51 -0400 Subject: Re: [compass-users] Magnetic Anomalies From: Luc Le Blanc Larry, If the magnetic anomaly is due to a DC current, wouldn't you need a deviation table (like on ships) that determines the correction needed at each azimuth? When plotted, this kind of table yields a sine curve that goes through zero at the azimuth of the magnetic source. Regards, Luc Le Blanc speleo.qc.ca/Auriga Le lun. 23 sept. 2019 18 h 56, 'Larry' [email protected] [compass-users] a Accrit : Hi Dave, Thanks for your email. I�?Tm not sure whether it would work or not. It would depend on whether the magnetic field from the power-lines was consistent. Here are some thoughts off the top of my head on the subject: The power-line voltage is alternating at 60 times per second. That would mean the magnetic field would be reversing 60 times per second. In other words, the magnetic field will oriented to magnetic-north for 1/120 of a second and magnetic-south for 1/120 of a second. A compass cannot respond 60 times per second so it would tend to average out the magnetic field. I would think the most you would see from the power lines is a slight vibration of the needle. So, in theory, the inertia of the needle should average out the reading and the net magnetic field would be zero. In other words, the flip between north and south poles should cancel out the magnetic field. However, since you are seeing distortions, there obviously must be some residual magnetic field from the power lines. Alternating current electricity produces all kinds of complicated effects that aren�?Tt easy to quantify. For example, the power lines can induce fields in nearby objects or even magnetic rocks in the ground that could last longer than 1/60 of a second. The main thing is whether the magnetic fields are consistent. If the fields don�?Tt change over time, then you should be able to use the concepts from the article to correct the compass reading in the cave. If they fluctuate over time, then the technique wouldn�?Tt be useful. I would suggest testing the consistency of the anomaly in the cave. To do this, you would go to a spot in the cave where the distortion is at a maximum and set the compass in a place where it cannot move. Then you would watch the needle over time and see if the compass reading changes. If it changes rapidly, it would be hard to use the technique. If it changes slowly or not at all, then you can use the technique. Since the magnetic correct relies on taking fore and back sights, the key question would be �?ocan you survey a front and back sight before the readings change?�?? If the readings are changing slowly enough, you should be able to take a fore and back sight before it changes. For example, if the readings are changing by one degree per minute, it is probably too fast to do front and back sites. However, if it is changing at one degree every ten minutes, you could probably get the readings needed to cancel out magnetic anomalies. If they are changing at one degree per hour, you shouldn�?Tt have any problem at all. Even if it was changing at one degree per minute, you could use two compasses, one for the fore sight and one for the back sight. However, you have to make sure that both compasses are calibrated so you they both get identical readings. Otherwise, you won�?Tt be able to tell if you are cancelling out magnetic distortion or just adding in the relative error between the two compasses. Another thought that just occurred to me is that they now sometimes transmit power using DC current instead of AC. If this is the case, the magnetic field should be consistent in direction and would only vary intensity based on the amount of current the lines are carrying. In that case, the anomaly should be fairly consistent, although you�?Td still want to do the test in the cave to see how much it changes over time. Let me know if you have any thoughts or questions. Larry Fish ------------------------------ *From:* [email protected] [mailto: [email protected]] *Sent:* Monday, September 23, 2019 11:14 AM *To:* Compass-Users *Subject:* [compass-users] Magnetic Anomalies Larry, I read the information given about Magnetic Anomalies when surveying in caves. Would the techniques apply to a cave that lies directly under a major power line? We get wild readings when we try to use a compass. - Dave Larry,If the magnetic anomaly is due to a DC current, wouldn't you need a deviation table (like on ships) that determines the correction needed at each azimuth? When plotted, this kind of table yields a sine curve that goes through zero at the azimuth of the magnetic source.Regards,-- Luc Le Blancspeleo.qc.ca/AurigaLe lun. 23 sept. 2019 18 h 56, 'Larry' [email protected] [compass-users] <[email protected]> a AccritA�: Hi Dave, Thanks for your email. I�?Tm not sure whether it would work or not. It would depend on whether the magnetic field from the power-lines was consistent. Here are some thoughts off the top of my head on the subject: The power-line voltage is alternating at 60 times per second. That would mean the magnetic field would be reversing 60 times per second. In other words, the magnetic field will oriented to magnetic-north for 1/120 of a second and magnetic-south for 1/120 of a second. A compass cannot respond 60 times per second so it would tend to average out the magnetic field. I would think the most you would see from the power lines is a slight vibration of the needle. So, in theory, the inertia of the needle should average out the reading and the net magnetic field would be zero. In other words, the flip between north and south poles should cancel out the magnetic field. However, since you are seeing distortions, there obviously must be some residual magnetic field from the power lines. Alternating current electricity produces all kinds of complicated effects that aren�?Tt easy to quantify. For example, the power lines can induce fields in nearby objects or even magnetic rocks in the ground that could last longer than 1/60 of a second. The main thing is whether the magnetic fields are consistent. If the fields don�?Tt change over time, then you should be able to use the concepts from the article to correct the compass reading in the cave. If they fluctuate over time, then the technique wouldn�?Tt be useful. I would suggest testing the consistency of the anomaly in the cave. To do this, you would go to a spot in the cave where the distortion is at a maximum and set the compass in a place where it cannot move. Then you would watch the needle over time and see if the compass reading changes. If it changes rapidly, it would be hard to use the technique. If it changes slowly or not at all, then you can use the technique. Since the magnetic correct relies on taking fore and back sights, the key question would be �?ocan you survey a front and back sight before the readings change?�?? If the readings are changing slowly enough, you should be able to take a fore and back sight before it changes. For example, if the readings are changing by one degree per minute, it is probably too fast to do front and back sites. However, if it is changing at one degree every ten minutes, you could probably get the readings needed to cancel out magnetic anomalies. If they are changing at one degree per hour, you shouldn�?Tt have any problem at all. Even if it was changing at one degree per minute, you could use two compasses, one for the fore sight and one for the back sight. However, you have to make sure that both compasses are calibrated so you they both get identical readings. Otherwise, you won�?Tt be able to tell if you are cancelling out magnetic distortion or just adding in the relative error between the two compasses. Another thought that just occurred to me is that they now sometimes transmit power using DC current instead of AC. If this is the case, the magnetic field should be consistent in direction and would only vary intensity based on the amount of current the lines are carrying. In that case, the anomaly should be fairly consistent, although you�?Td still want to do the test in the cave to see how much it changes over time. Let me know if you have any thoughts or questions. Larry Fish A� A� From: [email protected] [mailto:[email protected]] Sent: Monday, September 23, 2019 11:14 AM To: Compass-Users Subject: [compass-users] Magnetic Anomalies A� A� Larry, I read the information given about Magnetic Anomalies when surveying in caves. Would the techniques apply to a cave that lies directly under a major power line? We get wild readings when we try to use a compass. - Dave
Authentication-Results: mta4001.groups.mail.bf1.yahoo.com;
dkim=pass (ok) [email protected] header.s_fault;
spf=pass [email protected];
dmarc=pass(p=none sp=none dis=none) header.from=fountainware.com;
Date: Mon, 23 Sep 2019 18:25:43 -0600
Subject: RE: [compass-users] Magnetic Anomalies
From: "Larry"
Luc,
A deviation table would be nice, but I'm not sure how you'd make one. I
suppose you could map anomalies on the surface, but the magnetic distortion
probably changes with depth.
However, there is a way to figure out the distortion in the cave. Many years
ago, John Halleck wrote an article that shows how to use a compass to figure
out the magnetic anomaly at each survey station. His web site is no longer
on line, so you have to use the Wayback Machine to see it:
https://web.archive.org/web/20150718025752/http://www.cc.utah.edu/~nahaj/cav
e/survey/fore-back-example.html
John's article is a bit complicated, so I wrote a tutorial that walks
through the technique step by step. Here is a link to the article:
https://www.fountainware.com/compass/Tutorials/MagneticAnomalies/Anomalies.h
tm
Basically, John's idea works like this:
1. At the entrance to the cave, you use something like GPS to setup a line
on the surface that is calibrated to a precise azimuth. You then measure
this surface line with a compass. The difference between the calibrated line
and the compass reading is the magnet anomaly for the entrance station's
location.
2. You now take the first shot into the cave. Since you now know the anomaly
at the entrance station, you can correct for the magnetic anomaly on the
first shot. This removes any magnetic distortion from the first shot.
3. Next, you take a back sight from the "to" station back to the
entrance-station. Because the "to" station is in a different location, it
will have difference magnetic distortion. Since we've already corrected the
entrance shot, we know what the correct azimuth should be. As a result, the
difference between the correct azimuth and the back sight will be the
anomaly at the "to" station.
4. The process is repeated all through the cave, calculating the magnetic
distortion at each station.
Larry
_____
From: [email protected] [mailto:[email protected]]
Sent: Monday, September 23, 2019 5:20 PM
Subject: Re: [compass-users] Magnetic Anomalies
Larry,
If the magnetic anomaly is due to a DC current, wouldn't you need a
deviation table (like on ships) that determines the correction needed at
each azimuth? When plotted, this kind of table yields a sine curve that goes
through zero at the azimuth of the magnetic source.
Regards,
Luc Le Blanc
speleo.qc.ca/Auriga
Le lun. 23 sept. 2019 18 h 56, 'Larry' [email protected]
[compass-users] a �crit :
Hi Dave,
Thanks for your email. I'm not sure whether it would work or not. It would
depend on whether the magnetic field from the power-lines was consistent.
Here are some thoughts off the top of my head on the subject:
The power-line voltage is alternating at 60 times per second. That would
mean the magnetic field would be reversing 60 times per second. In other
words, the magnetic field will oriented to magnetic-north for 1/120 of a
second and magnetic-south for 1/120 of a second.
A compass cannot respond 60 times per second so it would tend to average out
the magnetic field. I would think the most you would see from the power
lines is a slight vibration of the needle. So, in theory, the inertia of the
needle should average out the reading and the net magnetic field would be
zero. In other words, the flip between north and south poles should cancel
out the magnetic field.
However, since you are seeing distortions, there obviously must be some
residual magnetic field from the power lines. Alternating current
electricity produces all kinds of complicated effects that aren't easy to
quantify. For example, the power lines can induce fields in nearby objects
or even magnetic rocks in the ground that could last longer than 1/60 of a
second.
The main thing is whether the magnetic fields are consistent. If the fields
don't change over time, then you should be able to use the concepts from the
article to correct the compass reading in the cave. If they fluctuate over
time, then the technique wouldn't be useful.
I would suggest testing the consistency of the anomaly in the cave. To do
this, you would go to a spot in the cave where the distortion is at a
maximum and set the compass in a place where it cannot move. Then you would
watch the needle over time and see if the compass reading changes. If it
changes rapidly, it would be hard to use the technique. If it changes slowly
or not at all, then you can use the technique.
Since the magnetic correct relies on taking fore and back sights, the key
question would be "can you survey a front and back sight before the readings
change?" If the readings are changing slowly enough, you should be able to
take a fore and back sight before it changes.
For example, if the readings are changing by one degree per minute, it is
probably too fast to do front and back sites. However, if it is changing at
one degree every ten minutes, you could probably get the readings needed to
cancel out magnetic anomalies. If they are changing at one degree per hour,
you shouldn't have any problem at all.
Even if it was changing at one degree per minute, you could use two
compasses, one for the fore sight and one for the back sight. However, you
have to make sure that both compasses are calibrated so you they both get
identical readings. Otherwise, you won't be able to tell if you are
cancelling out magnetic distortion or just adding in the relative error
between the two compasses.
Another thought that just occurred to me is that they now sometimes transmit
power using DC current instead of AC. If this is the case, the magnetic
field should be consistent in direction and would only vary intensity based
on the amount of current the lines are carrying. In that case, the anomaly
should be fairly consistent, although you'd still want to do the test in the
cave to see how much it changes over time.
Let me know if you have any thoughts or questions.
Larry Fish
_____
From: [email protected] [mailto:[email protected]]
Sent: Monday, September 23, 2019 11:14 AM
Subject: [compass-users] Magnetic Anomalies
Larry,
I read the information given about Magnetic Anomalies when surveying in
caves. Would the techniques apply to a cave that lies directly under a
major power line? We get wild readings when we try to use a compass.
- Dave
v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
st1\:*{behavior:url(#default#ieooui) }
Authentication-Results: mta4003.groups.mail.bf1.yahoo.com; dkim=pass (ok) [email protected] header.s=s201512; spf=pass [email protected]; dmarc=pass(p=none sp=NULL dis=none) header.from=qq.com; Date: Tue, 24 Sep 2019 09:43:01 +0800 Feedback-ID: riamail:qq.com:bgforeign:bgforeign4 Subject: Re: RE: [compass-users] Magnetic Anomalies From: "=?gb18030?B?wO7DyC3Ez8POweE=?=" hiIf it's really fast moving magnetic interference, I've used the following two methods before: 1.Measure the relative Angle between two wires on a plane projection�� 2.Use three sides of a triangle to calculate the Angle. By measuring the three wires forming the triangle, calculate the side length of the plane projection triangle and calculate the Angle.on�aY �aY ? hiIf it's really fast moving magnetic interference, I've used the following two methods before:1.Measure the relative Angle between two wires on a plane projection��2.Use three sides of a triangle to calculate the Angle.By measuring the three wires forming the triangle, calculate the side length of the plane projection triangle and calculate the Angle.
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dkim=pass (ok) [email protected] header.s 190202a;
spf=pass [email protected];
dmarc=pass(p=none sp=NULL dis=none) header.from=comcast.net;
Date: Mon, 23 Sep 2019 22:11:00 -0500
Subject: Re: [compass-users] Magnetic Anomalies
From: David Gerboth
Luc,
This sounds as complicated as a transit survey that we started to do in
the cave. A transit survey does not involve a compass.
- Dave
On 9/23/2019 7:25 PM, 'Larry' [email protected] [compass-users] wrote:
Luc,
A deviation table would be nice, but I'm not sure how you'd make one.
I suppose you could map anomalies on the surface, but the magnetic
distortion probably changes with depth.
However, there is a way to figure out the distortion in the cave. Many
years ago, John Halleck wrote an article that shows how to use a
compass to figure out the magnetic anomaly at each survey station. His
web site is no longer on line, so you have to use the Wayback Machine
to see it:
https://web.archive.org/web/20150718025752/http://www.cc.utah.edu/~nahaj/cave/survey/fore-back-example.html
John's article is a bit complicated, so I wrote a tutorial that walks
through the technique step by step. Here is a link to the article:
https://www.fountainware.com/compass/Tutorials/MagneticAnomalies/Anomalies.htm
Basically, John's idea works like this:
1. At the entrance to the cave, you use something like GPS to setup a
line on the surface that is calibrated to a precise azimuth. You then
measure this surface line with a compass. The difference between the
calibrated line and the compass reading is the magnet anomaly for the
entrance station's location.
2. You now take the first shot into the cave. Since you now know the
anomaly at the entrance station, you can correct for the magnetic
anomaly on the first shot. This removes any magnetic distortion from
the first shot.
3. Next, you take a back sight from the "to" station back to the
entrance-station. Because the "to" station is in a different location,
it will have difference magnetic distortion. Since we've already
corrected the entrance shot, we know what the correct azimuth should
be. As a result, the difference between the correct azimuth and the
back sight will be the anomaly at the "to" station.
4. The process is repeated all through the cave, calculating the
magnetic distortion at each station.
Larry
------------------------------------------------------------------------
*From:*[email protected]
[mailto:[email protected]]
*Sent:* Monday, September 23, 2019 5:20 PM
*To:* [email protected]
*Subject:* Re: [compass-users] Magnetic Anomalies
Larry,
If the magnetic anomaly is due to a DC current, wouldn't you need a
deviation table (like on ships) that determines the correction needed
at each azimuth? When plotted, this kind of table yields a sine curve
that goes through zero at the azimuth of the magnetic source.
Regards,
--
Luc Le Blanc
speleo.qc.ca/Auriga
Le lun. 23 sept. 2019 18 h 56, 'Larry' [email protected]
[compass-users]
a �crit�:
Hi Dave,
Thanks for your email. I'm not sure whether it would work or not.
It would depend on whether the magnetic field from the power-lines
was consistent. Here are some thoughts off the top of my head on
the subject:
The power-line voltage is alternating at 60 times per second. That
would mean the magnetic field would be reversing 60 times per
second. In other words, the magnetic field will oriented to
magnetic-north for 1/120 of a second and magnetic-south for 1/120
of a second.
A compass cannot respond 60 times per second so it would tend to
average out the magnetic field. I would think the most you would
see from the power lines is a slight vibration of the needle. So,
in theory, the inertia of the needle should average out the
reading and the net magnetic field would be zero. In other words,
the flip between north and south poles should cancel out the
magnetic field.
However, since you are seeing distortions, there obviously must be
some residual magnetic field from the power lines. Alternating
current electricity produces all kinds of complicated effects that
aren't easy to quantify. For example, the power lines can induce
fields in nearby objects or even magnetic rocks in the ground that
could last longer than 1/60 of a second.
The main thing is whether the magnetic fields are consistent. If
the fields don't change over time, then you should be able to use
the concepts from the article to correct the compass reading in
the cave. If they fluctuate over time, then the technique wouldn't
be useful.
I would suggest testing the consistency of the anomaly in the
cave. To do this, you would go to a spot in the cave where the
distortion is at a maximum and set the compass in a place where it
cannot move. Then you would watch the needle over time and see if
the compass reading changes. If it changes rapidly, it would be
hard to use the technique. If it changes slowly or not at all,
then you can use the technique.
Since the magnetic correct relies on taking fore and back sights,
the key question would be "can you survey a front and back sight
before the readings change?" If the readings are changing slowly
enough, you should be able to take a fore and back sight before it
changes.
For example, if the readings are changing by one degree per
minute, it is probably too fast to do front and back sites.
However, if it is changing at one degree every ten minutes, you
could probably get the readings needed to cancel out magnetic
anomalies.. If they are changing at one degree per hour, you
shouldn't have any problem at all.
Even if it was changing at one degree per minute, you could use
two compasses, one for the fore sight and one for the back sight.
However, you have to make sure that both compasses are calibrated
so you they both get identical readings. Otherwise, you won't be
able to tell if you are cancelling out magnetic distortion or just
adding in the relative error between the two compasses.
Another thought that just occurred to me is that they now
sometimes transmit power using DC current instead of AC. If this
is the case, the magnetic field should be consistent in direction
and would only vary intensity based on the amount of current the
lines are carrying. In that case, the anomaly should be fairly
consistent, although you'd still want to do the test in the cave
to see how much it changes over time.
Let me know if you have any thoughts or questions.
Larry Fish
------------------------------------------------------------------------
*From:*[email protected]
[mailto:[email protected]
]
*Sent:* Monday, September 23, 2019 11:14 AM
*To:* Compass-Users
*Subject:* [compass-users] Magnetic Anomalies
Larry,
I read the information given about Magnetic Anomalies when
surveying in
caves. Would the techniques apply to a cave that lies directly
under a
major power line? We get wild readings when we try to use a compass.
- Dave
Luc,
This sounds as complicated as a transit
survey that we started to do in the cave. A transit survey does
not involve a compass.
- Dave
On 9/23/2019 7:25 PM, 'Larry'
[email protected] [compass-users] wrote:
�
Luc,
A
deviation table would be nice, but I'm not sure how
you'd make one. I suppose you could map anomalies on
the surface, but the
magnetic distortion probably changes with depth.
However,
there is a way to figure out the distortion in the
cave. Many years ago, John Halleck wrote an article
that shows how to use a
compass to figure out the magnetic anomaly at each
survey station. His web site
is no longer on line, so you have to use the Wayback
Machine to see it:
https://web.archive.org/web/20150718025752/http://www.cc.utah.edu/~nahaj/cave/survey/fore-back-example.html
John's article is a bit complicated, so I
wrote a tutorial that
walks through the technique step by step. Here is a
link to the article:
https://www.fountainware.com/compass/Tutorials/MagneticAnomalies/Anomalies.htm
Basically, John's idea works like this:
1. At the entrance to the cave, you use
something like GPS to setup a
line on the surface that is calibrated to a precise
azimuth. You then measure
this surface line with a compass. The difference
between the calibrated line
and the compass reading is the magnet anomaly for
the entrance station's
location.
2. You now take the first shot into the
cave. Since you now know the
anomaly at the entrance station, you can correct for
the magnetic anomaly on
the first shot. This removes any magnetic distortion
from the first shot.
3. Next, you take a back sight from the
"to" station back
to the entrance-station. Because the "to" station is
in a different
location, it will have difference magnetic
distortion. Since we've
already corrected the entrance shot, we know what
the correct azimuth should be.
As a result, the difference between the correct
azimuth and the back sight will
be the anomaly at the "to" station.
4. The process is repeated all through the
cave, calculating the
magnetic distortion at each station.
Larry
�
�
From: [email protected]
[mailto:[email protected]]
Sent:
Monday, September 23, 2019
5:20 PM
To:
[email protected]
Subject:
Re: [compass-users]
Magnetic Anomalies
�
�
Larry,
�
If the magnetic anomaly is due to
a DC current, wouldn't you need a
deviation table (like on ships) that
determines the correction needed at each
azimuth? When plotted, this kind of table
yields a sine curve that goes through
zero at the azimuth of the magnetic
source.
�
Regards,
�
--
Luc Le Blanc
speleo.qc.ca/Auriga
�
Le lun. 23 sept. 2019 18 h 56,
'Larry' [email protected]
[compass-users]
<[email protected]>
a �crit�:
�
Hi
Dave,
Thanks
for
your email. I'm not sure whether it
would work or not. It would depend on
whether the magnetic field from the
power-lines was consistent. Here are
some
thoughts off the top of my head on the
subject:
The
power-line voltage is alternating at
60 times per second. That would mean
the
magnetic field would be reversing 60
times per second. In other words, the
magnetic field will oriented to
magnetic-north for 1/120 of a second
and
magnetic-south for 1/120 of a second.
A
compass
cannot respond 60 times per second so
it would tend to average out the
magnetic
field. I would think the most you
would see from the power lines is a
slight
vibration of the needle. So, in
theory, the inertia of the needle
should
average out the reading and the net
magnetic field would be zero. In other
words, the flip between north and
south poles should cancel out the
magnetic
field.
However,
since you are seeing distortions,
there obviously must be some residual
magnetic field from the power lines.
Alternating current electricity
produces
all kinds of complicated effects that
aren't easy to quantify. For example,
the power lines can induce fields in
nearby objects or even magnetic rocks
in
the ground that could last longer than
1/60 of a second.
The main
thing is
whether the magnetic fields are
consistent. If the fields don't change
over time, then you should be able to
use the concepts from the article to
correct the compass reading in the
cave. If they fluctuate over time,
then the
technique wouldn't be useful.
I would
suggest
testing the consistency of the anomaly
in the cave. To do this, you would go
to
a spot in the cave where the
distortion is at a maximum and set the
compass in
a place where it cannot move. Then you
would watch the needle over time and
see
if the compass reading changes. If it
changes rapidly, it would be hard to
use
the technique. If it changes slowly or
not at all, then you can use the
technique.
Since the
magnetic
correct relies on taking fore and back
sights, the key question would be
"can you survey a front and back sight
before the readings change?"
If the readings are changing slowly
enough, you should be able to take a
fore
and back sight before it changes.
For example,
if
the readings are changing by one
degree per minute, it is probably too
fast to
do front and back sites. However, if
it is changing at one degree every ten
minutes,
you could probably get the readings
needed to cancel out magnetic
anomalies.. If
they are changing at one degree per
hour, you shouldn't have any problem
at all.
Even if it
was
changing at one degree per minute, you
could use two compasses, one for the
fore sight and one for the back sight.
However, you have to make sure that
both
compasses are calibrated so you they
both get identical readings.
Otherwise,
you won't be able to tell if you are
cancelling out magnetic distortion
or just adding in the relative error
between the two compasses.
Another
thought
that just occurred to me is that they
now sometimes transmit power using DC
current instead of AC. If this is the
case, the magnetic field should be
consistent in direction and would only
vary intensity based on the amount of
current the lines are carrying. In
that case, the anomaly should be
fairly
consistent, although you'd still want
to do the test in the cave to see
how much it changes over time.
Let me know
if you
have any thoughts or questions.
Larry Fish
�
�
From: [email protected]
[mailto:[email protected]]
Sent:
Monday, September 23, 2019
11:14 AM
To:
Compass-Users
Subject:
[compass-users] Magnetic
Anomalies
�
�
Larry,
I read the information given
about Magnetic Anomalies when
surveying in
caves. Would the techniques
apply to a cave that lies
directly under a
major power line? We get wild
readings when we try to use a
compass.
- Dave
�
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Date: Mon, 23 Sep 2019 23:39:12 -0400
Subject: Re: [compass-users] Magnetic Anomalies
From: Luc Le Blanc
Hi,
If I were you, I'd first try to establish a deviation table at the cave
entrance and apply it to the existing survey shots to see whether it helps.
If you're lucky enough to have a loop in your survey, it'll be easier to
determine the improvement. From there, you can decide if you need to use a
more complex solution. My 2A�.
Luc Le Blanc
http://www.speleo.qc.ca/Auriga
Le lun. 23 sept. 2019 23:11, David Gerboth [email protected]
[compass-users] a Accrit :
Luc,
This sounds as complicated as a transit survey that we started to do in
the cave. A transit survey does not involve a compass.
- Dave
On 9/23/2019 7:25 PM, 'Larry' [email protected] [compass-users]
wrote:
Luc,
A deviation table would be nice, but I�?Tm not sure how you�?Td make one. I
suppose you could map anomalies on the surface, but the magnetic distortion
probably changes with depth.
However, there is a way to figure out the distortion in the cave. Many
years ago, John Halleck wrote an article that shows how to use a compass to
figure out the magnetic anomaly at each survey station. His web site is no
longer on line, so you have to use the Wayback Machine to see it:
https://web.archive.org/web/20150718025752/http://www.cc.utah.edu/~nahaj/cave/survey/fore-back-example.html
John�?Ts article is a bit complicated, so I wrote a tutorial that walks
through the technique step by step. Here is a link to the article:
https://www.fountainware.com/compass/Tutorials/MagneticAnomalies/Anomalies.htm
Basically, John�?Ts idea works like this:
1. At the entrance to the cave, you use something like GPS to setup a line
on the surface that is calibrated to a precise azimuth. You then measure
this surface line with a compass. The difference between the calibrated
line and the compass reading is the magnet anomaly for the entrance
station�?Ts location.
2. You now take the first shot into the cave. Since you now know the
anomaly at the entrance station, you can correct for the magnetic anomaly
on the first shot. This removes any magnetic distortion from the first
shot.
3. Next, you take a back sight from the �?oto�?? station back to the
entrance-station. Because the �?oto�?? station is in a different location, it
will have difference magnetic distortion. Since we�?Tve already corrected the
entrance shot, we know what the correct azimuth should be. As a result, the
difference between the correct azimuth and the back sight will be the
anomaly at the �?oto�?? station.
4. The process is repeated all through the cave, calculating the magnetic
distortion at each station.
Larry
------------------------------
*From:* [email protected] [mailto:
[email protected]]
*Sent:* Monday, September 23, 2019 5:20 PM
*To:* [email protected]
*Subject:* Re: [compass-users] Magnetic Anomalies
Larry,
If the magnetic anomaly is due to a DC current, wouldn't you need a
deviation table (like on ships) that determines the correction needed at
each azimuth? When plotted, this kind of table yields a sine curve that
goes through zero at the azimuth of the magnetic source.
Regards,
--
Luc Le Blanc
speleo.qc.ca/Auriga
Le lun. 23 sept. 2019 18 h 56, 'Larry' [email protected]
[compass-users] a Accrit :
Hi Dave,
Thanks for your email. I�?Tm not sure whether it would work or not. It would
depend on whether the magnetic field from the power-lines was consistent.
Here are some thoughts off the top of my head on the subject:
The power-line voltage is alternating at 60 times per second. That would
mean the magnetic field would be reversing 60 times per second. In other
words, the magnetic field will oriented to magnetic-north for 1/120 of a
second and magnetic-south for 1/120 of a second.
A compass cannot respond 60 times per second so it would tend to average
out the magnetic field. I would think the most you would see from the power
lines is a slight vibration of the needle. So, in theory, the inertia of
the needle should average out the reading and the net magnetic field would
be zero. In other words, the flip between north and south poles should
cancel out the magnetic field.
However, since you are seeing distortions, there obviously must be some
residual magnetic field from the power lines. Alternating current
electricity produces all kinds of complicated effects that aren�?Tt easy to
quantify. For example, the power lines can induce fields in nearby objects
or even magnetic rocks in the ground that could last longer than 1/60 of a
second.
The main thing is whether the magnetic fields are consistent. If the
fields don�?Tt change over time, then you should be able to use the concepts
from the article to correct the compass reading in the cave. If they
fluctuate over time, then the technique wouldn�?Tt be useful.
I would suggest testing the consistency of the anomaly in the cave. To do
this, you would go to a spot in the cave where the distortion is at a
maximum and set the compass in a place where it cannot move. Then you would
watch the needle over time and see if the compass reading changes. If it
changes rapidly, it would be hard to use the technique. If it changes
slowly or not at all, then you can use the technique.
Since the magnetic correct relies on taking fore and back sights, the key
question would be �?ocan you survey a front and back sight before the
readings change?�?? If the readings are changing slowly enough, you should be
able to take a fore and back sight before it changes.
For example, if the readings are changing by one degree per minute, it is
probably too fast to do front and back sites. However, if it is changing at
one degree every ten minutes, you could probably get the readings needed to
cancel out magnetic anomalies.. If they are changing at one degree per
hour, you shouldn�?Tt have any problem at all.
Even if it was changing at one degree per minute, you could use two
compasses, one for the fore sight and one for the back sight. However, you
have to make sure that both compasses are calibrated so you they both get
identical readings. Otherwise, you won�?Tt be able to tell if you are
cancelling out magnetic distortion or just adding in the relative error
between the two compasses.
Another thought that just occurred to me is that they now sometimes
transmit power using DC current instead of AC. If this is the case, the
magnetic field should be consistent in direction and would only vary
intensity based on the amount of current the lines are carrying. In that
case, the anomaly should be fairly consistent, although you�?Td still want to
do the test in the cave to see how much it changes over time.
Let me know if you have any thoughts or questions.
Larry Fish
------------------------------
*From:* [email protected] [mailto:
[email protected]]
*Sent:* Monday, September 23, 2019 11:14 AM
*To:* Compass-Users
*Subject:* [compass-users] Magnetic Anomalies
Larry,
I read the information given about Magnetic Anomalies when surveying in
caves. Would the techniques apply to a cave that lies directly under a
major power line? We get wild readings when we try to use a compass.
- Dave
Hi,If I were you, I'd first try to establish a deviation table at the cave entrance and apply it to the existing survey shots to see whether it helps. If you're lucky enough to have a loop in your survey, it'll be easier to determine the improvement. From there, you can decide if you need to use a more complex solution. My 2A�.-- Luc Le Blanchttp://www.speleo.qc.ca/AurigaLe lun. 23 sept. 2019 23:11, David Gerboth [email protected] [compass-users] <[email protected]> a AccritA�:
Luc,
This sounds as complicated as a transit
survey that we started to do in the cave. A transit survey does
not involve a compass.
- Dave
On 9/23/2019 7:25 PM, 'Larry'
[email protected] [compass-users] wrote:
A�
Luc,
A
deviation table would be nice, but I�?Tm not sure how
you�?Td make one. I suppose you could map anomalies on
the surface, but the
magnetic distortion probably changes with depth.
However,
there is a way to figure out the distortion in the
cave. Many years ago, John Halleck wrote an article
that shows how to use a
compass to figure out the magnetic anomaly at each
survey station. His web site
is no longer on line, so you have to use the Wayback
Machine to see it:
https://web.archive.org/web/20150718025752/http://www.cc.utah.edu/~nahaj/cave/survey/fore-back-example.html
John�?Ts article is a bit complicated, so I
wrote a tutorial that
walks through the technique step by step. Here is a
link to the article:
https://www.fountainware.com/compass/Tutorials/MagneticAnomalies/Anomalies.htm
Basically, John�?Ts idea works like this:
1. At the entrance to the cave, you use
something like GPS to setup a
line on the surface that is calibrated to a precise
azimuth. You then measure
this surface line with a compass. The difference
between the calibrated line
and the compass reading is the magnet anomaly for
the entrance station�?Ts
location.
2. You now take the first shot into the
cave. Since you now know the
anomaly at the entrance station, you can correct for
the magnetic anomaly on
the first shot. This removes any magnetic distortion
from the first shot.
3. Next, you take a back sight from the
�?oto�?? station back
to the entrance-station. Because the �?oto�?? station is
in a different
location, it will have difference magnetic
distortion. Since we�?Tve
already corrected the entrance shot, we know what
the correct azimuth should be.
As a result, the difference between the correct
azimuth and the back sight will
be the anomaly at the �?oto�?? station.
4. The process is repeated all through the
cave, calculating the
magnetic distortion at each station.
Larry
A�
A�
From: [email protected]
[mailto:[email protected]]
Sent:
Monday, September 23, 2019
5:20 PM
To:
[email protected]
Subject:
Re: [compass-users]
Magnetic Anomalies
A�
A�
Larry,
A�
If the magnetic anomaly is due to
a DC current, wouldn't you need a
deviation table (like on ships) that
determines the correction needed at each
azimuth? When plotted, this kind of table
yields a sine curve that goes through
zero at the azimuth of the magnetic
source.
A�
Regards,
A�
--
Luc Le Blanc
speleo.qc.ca/Auriga
A�
Le lun. 23 sept. 2019 18 h 56,
'Larry' [email protected]
[compass-users]
<[email protected]>
a AccritA�:
A�
Hi
Dave,
Thanks
for
your email. I�?Tm not sure whether it
would work or not. It would depend on
whether the magnetic field from the
power-lines was consistent. Here are
some
thoughts off the top of my head on the
subject:
The
power-line voltage is alternating at
60 times per second. That would mean
the
magnetic field would be reversing 60
times per second. In other words, the
magnetic field will oriented to
magnetic-north for 1/120 of a second
and
magnetic-south for 1/120 of a second.
A
compass
cannot respond 60 times per second so
it would tend to average out the
magnetic
field. I would think the most you
would see from the power lines is a
slight
vibration of the needle. So, in
theory, the inertia of the needle
should
average out the reading and the net
magnetic field would be zero. In other
words, the flip between north and
south poles should cancel out the
magnetic
field.
However,
since you are seeing distortions,
there obviously must be some residual
magnetic field from the power lines.
Alternating current electricity
produces
all kinds of complicated effects that
aren�?Tt easy to quantify. For example,
the power lines can induce fields in
nearby objects or even magnetic rocks
in
the ground that could last longer than
1/60 of a second.
The main
thing is
whether the magnetic fields are
consistent. If the fields don�?Tt change
over time, then you should be able to
use the concepts from the article to
correct the compass reading in the
cave. If they fluctuate over time,
then the
technique wouldn�?Tt be useful.
I would
suggest
testing the consistency of the anomaly
in the cave. To do this, you would go
to
a spot in the cave where the
distortion is at a maximum and set the
compass in
a place where it cannot move. Then you
would watch the needle over time and
see
if the compass reading changes. If it
changes rapidly, it would be hard to
use
the technique. If it changes slowly or
not at all, then you can use the
technique.
Since the
magnetic
correct relies on taking fore and back
sights, the key question would be
�?ocan you survey a front and back sight
before the readings change?�??
If the readings are changing slowly
enough, you should be able to take a
fore
and back sight before it changes.
For example,
if
the readings are changing by one
degree per minute, it is probably too
fast to
do front and back sites. However, if
it is changing at one degree every ten
minutes,
you could probably get the readings
needed to cancel out magnetic
anomalies.. If
they are changing at one degree per
hour, you shouldn�?Tt have any problem
at all.
Even if it
was
changing at one degree per minute, you
could use two compasses, one for the
fore sight and one for the back sight.
However, you have to make sure that
both
compasses are calibrated so you they
both get identical readings.
Otherwise,
you won�?Tt be able to tell if you are
cancelling out magnetic distortion
or just adding in the relative error
between the two compasses.
Another
thought
that just occurred to me is that they
now sometimes transmit power using DC
current instead of AC. If this is the
case, the magnetic field should be
consistent in direction and would only
vary intensity based on the amount of
current the lines are carrying. In
that case, the anomaly should be
fairly
consistent, although you�?Td still want
to do the test in the cave to see
how much it changes over time.
Let me know
if you
have any thoughts or questions.
Larry Fish
A�
A�
From: [email protected]
[mailto:[email protected]]
Sent:
Monday, September 23, 2019
11:14 AM
To:
Compass-Users
Subject:
[compass-users] Magnetic
Anomalies
A�
A�
Larry,
I read the information given
about Magnetic Anomalies when
surveying in
caves. Would the techniques
apply to a cave that lies
directly under a
major power line? We get wild
readings when we try to use a
compass.
- Dave
A�
Authentication-Results: mta4004.groups.mail.bf1.yahoo.com;
dkim=neutral (no sig) [email protected];
spf=pass [email protected];
dmarc=NULL(p=NULL sp=NULL dis=NULL) header.from=netnet.net;
Date: Tue, 24 Sep 2019 10:40:20 -0500
Subject: RE: [compass-users] Magnetic Anomalies
From: "Anthony J. Kroes"
Larry,
Wouldn't the orientation of the power lines also be a factor? It the Power
lines are oriented NE/SW (or whatever you choose) wouldn't the magnetic
field align with that instead of N/S since it would be so much more powerful
(locally) than the Earth's magnetic field?
Either way, your info about the field fluctuating back and forth and
therefore not much movement in the needle would still be true - it just
wouldn't point N, but it would be consistently off at any one particular
spot. Moving through the cave would give readings that are off differently
at different locations, but each location would give consistent readings
with itself.
N%�
From: [email protected]
Sent: Monday, September 23, 2019 5:56 PM
Subject: RE: [compass-users] Magnetic Anomalies
Hi Dave,
Thanks for your email. I'm not sure whether it would work or not. It would
depend on whether the magnetic field from the power-lines was consistent.
Here are some thoughts off the top of my head on the subject:
The power-line voltage is alternating at 60 times per second. That would
mean the magnetic field would be reversing 60 times per second. In other
words, the magnetic field will oriented to magnetic-north for 1/120 of a
second and magnetic-south for 1/120 of a second.
A compass cannot respond 60 times per second so it would tend to average out
the magnetic field. I would think the most you would see from the power
lines is a slight vibration of the needle. So, in theory, the inertia of the
needle should average out the reading and the net magnetic field would be
zero. In other words, the flip between north and south poles should cancel
out the magnetic field.
However, since you are seeing distortions, there obviously must be some
residual magnetic field from the power lines. Alternating current
electricity produces all kinds of complicated effects that aren't easy to
quantify. For example, the power lines can induce fields in nearby objects
or even magnetic rocks in the ground that could last longer than 1/60 of a
second.
The main thing is whether the magnetic fields are consistent. If the fields
don't change over time, then you should be able to use the concepts from the
article to correct the compass reading in the cave. If they fluctuate over
time, then the technique wouldn't be useful.
I would suggest testing the consistency of the anomaly in the cave. To do
this, you would go to a spot in the cave where the distortion is at a
maximum and set the compass in a place where it cannot move. Then you would
watch the needle over time and see if the compass reading changes. If it
changes rapidly, it would be hard to use the technique. If it changes slowly
or not at all, then you can use the technique.
Since the magnetic correct relies on taking fore and back sights, the key
question would be "can you survey a front and back sight before the readings
change?" If the readings are changing slowly enough, you should be able to
take a fore and back sight before it changes.
For example, if the readings are changing by one degree per minute, it is
probably too fast to do front and back sites. However, if it is changing at
one degree every ten minutes, you could probably get the readings needed to
cancel out magnetic anomalies. If they are changing at one degree per hour,
you shouldn't have any problem at all.
Even if it was changing at one degree per minute, you could use two
compasses, one for the fore sight and one for the back sight. However, you
have to make sure that both compasses are calibrated so you they both get
identical readings. Otherwise, you won't be able to tell if you are
cancelling out magnetic distortion or just adding in the relative error
between the two compasses.
Another thought that just occurred to me is that they now sometimes transmit
power using DC current instead of AC. If this is the case, the magnetic
field should be consistent in direction and would only vary intensity based
on the amount of current the lines are carrying. In that case, the anomaly
should be fairly consistent, although you'd still want to do the test in the
cave to see how much it changes over time.
Let me know if you have any thoughts or questions.
Larry Fish
_____
From: [email protected] [mailto:[email protected]]
Sent: Monday, September 23, 2019 11:14 AM
Subject: [compass-users] Magnetic Anomalies
Larry,
I read the information given about Magnetic Anomalies when surveying in
caves. Would the techniques apply to a cave that lies directly under a
major power line? We get wild readings when we try to use a compass.
- Dave
v\:* {behavior:url(#default#VML);}
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Date: Wed, 25 Sep 2019 00:40:08 +0800
Feedback-ID: webmail:qq.com:bgweb:bgweb2
Subject: RE: [compass-users] Magnetic Anomalies
From: "=?utf-8?B?5p2O6JCMLeWNl+aipueOsg==?="
......
Please forgive me for not good English.
I seem to confuse the two words �?owiress�?? and �?oline�??.
Li Meng
------------------ �ZY�<�,r�� ------------------
�?`�����: "compass-users";
�?`�??�-�-': 2019�1'9�o^24�-�(�~Y�oY��O) �,S�?^9:43
�"�����: "compass-users";
�,���~: Re: RE: [compass-users] Magnetic Anomalies
hi
If it's really fast moving magnetic interference, I've used the following two methods before:
1.Measure the relative Angle between two wires on a plane projectiona?,
2.Use three sides of a triangle to calculate the Angle.
By measuring the three wires forming the triangle, calculate the side length of the plane projection triangle and calculate the Angle.
......Please forgive me for not good English.I seem to confuse the two words �?owiress�?? and �?oline�??.Li Meng------------------ �ZY�<�,r�� ------------------�?`�����: "compass-users"<[email protected]>;�?`�??�-�-': 2019�1'9�o^24�-�(�~Y�oY��O) �,S�?^9:43�"�����: "compass-users"<[email protected]>;�,���~: Re: RE: [compass-users] Magnetic Anomalies
hiIf it's really fast moving magnetic interference, I've used the following two methods before:1.Measure the relative Angle between two wires on a plane projectiona?,2.Use three sides of a triangle to calculate the Angle.By measuring the three wires forming the triangle, calculate the side length of the plane projection triangle and calculate the Angle.
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dkim=pass (ok) [email protected] header.s_fault;
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Date: Tue, 24 Sep 2019 12:44:16 -0600
Subject: RE: [compass-users] Magnetic Anomalies
From: "Larry"
Li Meng,
Your English is fine. As a long-time learner of Spanish, I know how easy it
is to get the subtle differences between different words right when you are
working in a foreign language.
When I read your post, I assumed you meant ��line�� or ��shot�� when you
said ��wire.��
In English, ��wire�� tends to refer to the long, round, thin metal things
that are used to carry electricity. ��Line�� is a better choice. When
referring to surveying, the word ��shot�� is often be used. Some people use
the word ��leg.��
I understood your equations, so there was no problem there.
I wasn�_t quite sure what you meant by ��fast moving magnetic interference��
and how you actually applied it in the field. I�_d be very interesting in
more information about how your technique works.
Larry
_____
From: [email protected] [mailto:[email protected]]
Sent: Tuesday, September 24, 2019 10:40 AM
Subject: RE: [compass-users] Magnetic Anomalies
......
Please forgive me for not good English.
I seem to confuse the two words ��wiress�� and ��line��.
Li Meng
���_EE: "compass-users";
��EIE�: 2019��9OA24EO(D��U_) �II�9:43
EO�_EE: "compass-users";
��I�: Re: RE: [compass-users] Magnetic Anomalies
hi
If it's really fast moving magnetic interference, I've used the following
two methods before:
1.Measure the relative Angle between two wires on a plane projection��
2.Use three sides of a triangle to calculate the Angle.
By measuring the three wires forming the triangle, calculate the side length
of the plane projection triangle and calculate the Angle.
v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
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Authentication-Results: mta4001.groups.mail.ne1.yahoo.com; dkim=pass (ok) [email protected] header.s_fault; spf=pass [email protected]; dmarc=pass(p=none sp=none dis=none) header.from=fountainware.com; Date: Tue, 24 Sep 2019 13:43:53 -0600 Subject: RE: [compass-users] Magnetic Anomalies From: "Larry" Tony, Good question. I think the orientation of the compass will be the sum of the two field vectors. If the power-line field is very strong, it will overwhelm the Earth's magnetic field and dominate. However, as long as it is not too strong, you still should be able to work out the magnetic anomaly and remove it. For example, let's say you take the calibrating shot at the entrance to the cave. If the calibrating shot was to the North and you normalized the Earth's magnetic field-strength to one, you'd have this field vector: [1,0] Likewise, if you have power-line field oriented due East that was 10 times stronger than the Earth's field, you would have a vector of: [0,10] The sum of those vectors would be: [1,10] So the compass-angle would be: 84.2 degrees When you read the compass at this point, it will read 84.2 degrees but because you know the actual direction of the calibrated shot is due north, the magnetic anomaly will be 84.2 degrees and will be the same for any other shot taken from the position. In this case, the Earth magnetic field is still producing 5.8 degrees of deflection on the compass. That is getting close to the accuracy limit of the compass. If the field were much stronger, the Earth's magnetic field will be buried by random error. However, the power line field intensity decreases rapidly with distance. Normally, it would be with the square of the distance, but in some instances it decreases faster: http://www.emfs.info/sources/overhead/physics/power-law/ Typically, high-voltage power lines are many feet off the ground. Also, the further underground the cave is, the less influence the power lines will have on the survey. If the power lines are carrying AC current, there will be some canceling effect of the magnetic field. Like wise, if you have two conductors that are 180 degrees out of phase with each other, they will tend to cancel the magnetic field. It would be interesting to know just how strong the residual magnetic field is and how quickly it decreases with distance. It would be easy to do the experiment described above and figure it out. Larry _____ From: [email protected] [mailto:[email protected]] Sent: Tuesday, September 24, 2019 9:40 AM Subject: RE: [compass-users] Magnetic Anomalies Larry, Wouldn't the orientation of the power lines also be a factor? It the Power lines are oriented NE/SW (or whatever you choose) wouldn't the magnetic field align with that instead of N/S since it would be so much more powerful (locally) than the Earth's magnetic field? Either way, your info about the field fluctuating back and forth and therefore not much movement in the needle would still be true - it just wouldn't point N, but it would be consistently off at any one particular spot. Moving through the cave would give readings that are off differently at different locations, but each location would give consistent readings with itself. N%�n
Authentication-Results: mta4002.groups.mail.bf1.yahoo.com; dkim=pass (ok) [email protected] header.s=s201512; spf=pass [email protected]; dmarc=pass(p=none sp=NULL dis=none) header.from=qq.com; Date: Wed, 25 Sep 2019 14:38:36 +0800 Feedback-ID: riamail:qq.com:bgforeign:bgforeign4 Subject: RE: [compass-users] Magnetic Anomalies From: "=?gb18030?B?wO7DyC3Ez8POweE=?=" Larry�� I used the wrong word ��fast moving��......Rapid change, instability, periodic oscillation�� In guiyang, China, there is a cave with a hydroelectric power station My specific implementation plan is: For the distox2 scheme of triangulation. Three people,One person as �� instrument person�� (A station), two people as�� front person �� (B, C station)The hole uses two gps to correct the magnetic field anomaly. Start station A, measure A-B and A-C, then move �� instrument person�� to B, measure B-C, repeat the process and advance. (A-B, A-C, B-C, B-D, C-D, C-E, D-E........) (difficulty in Pit) Need to pay attention to the left and right sides of the triangle. After returning home, use the programmed program to calculate the azimuth uniformly. The topodroid software also has a triangle loop closure, and the screenshot is a description of the topodroid. Li Meng ---Original--- From: "'Larry' [email protected] [compass-users]"
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dmarc=pass(p=none sp=none dis=none) header.from=fountainware.com;
Date: Wed, 25 Sep 2019 13:22:55 -0600
Subject: RE: [compass-users] Magnetic Anomalies
From: "Larry"
Li Meng,
This is a very interesting idea. If I understand what you are doing
correctly, if you establish one shot with an accurate azimuth, you can then
simply measure the distance between each end of the shot to a new station.
This forms a triangle. Knowing the lengths of the sides of the triangle,
allows you to calculate the azimuth angles in a way that completely avoids
any magnetic anomalies.
This is similar to what land-surveyors with ��triangulation networks,��
except that they are measuring angles instead of lengths.
https://www.e-education.psu.edu/natureofgeoinfo/c5_p11.html
One issue with this method is the accumulation of errors. With the standard
compass-tape-inclinometer method used by cave surveyors, the compass angle
is re-referenced to magnetic north each time you take an azimuth reading. In
other words, every time you take a compass reading, it is always relative
the magnetic north. That means that the azimuth errors don�_t add up as you
survey through a cave.
The same thing happens with the inclinometer readings. The inclination angle
is always re-referenced to the Earth�_s gravity field, so errors don�_t add
up.
With a land-survey, you measure angles between shots. As a result, an
angle-error in the first shot is added to the error in the second shot and
so on throughout the cave. This can add up to large errors at the end of the
survey. For this reason, very accurate instruments (theodolites) and very
accurate measurements are required.
The same thing could happen when measuring the sides of a triangle. While
tape measurements are probably more accurate than angle measurements, the
errors would still add up and the calculated azimuth could be less accurate
than similar measurements with a compass. That probably means the method is
best used to deal with local magnetic anomalies. You probably wouldn�_t want
to use it to cover large distances in the cave.
One advantage of the John Hallack�_s method is that doesn�_t really change
the way you survey in the cave. Once you establish the base shot at the
entrance, you just take normal fore and back sights. The difference comes
when you process the data. Instead of just averaging the fore and back
sights, you calculate the magnetic-anomaly at each station and use it to
correct the azimuth for every shot that originates from that station.
Larry
_____
From: [email protected] [mailto:[email protected]]
Sent: Wednesday, September 25, 2019 12:39 AM
Subject: RE: [compass-users] Magnetic Anomalies
Larry��
I used the wrong word ��fast moving��......Rapid change, instability,
periodic oscillation��
In guiyang, China, there is a cave with a hydroelectric power station
My specific implementation plan is:
For the distox2 scheme of triangulation.
Three people,One person as �� instrument person�� (A station), two people
as�� front person �� (B, C station)The hole uses two gps to correct the
magnetic field anomaly.
Start station A, measure A-B and A-C,
then move �� instrument person�� to B,
measure B-C,
repeat the process and advance. (A-B, A-C, B-C, B-D, C-D, C-E, D-E........)
(difficulty in Pit)
Need to pay attention to the left and right sides of the triangle.
After returning home, use the programmed program to calculate the azimuth
uniformly.
The topodroid software also has a triangle loop closure, and the screenshot
is a description of the topodroid.
Li Meng
From: "'Larry' [email protected]
[compass-users]"
Date: Wed, Sep 25, 2019 03:26 AM
Subject: RE: [compass-users] Magnetic Anomalies
Li Meng,
Your English is fine. As a long-time learner of Spanish, I know how easy it
is to get the subtle differences between different words right when you are
working in a foreign language.
When I read your post, I assumed you meant ��line�� or ��shot�� when you
said ��wire.��
In English, ��wire�� tends to refer to the long, round, thin metal things
that are used to carry electricity. ��Line�� is a better choice. When
referring to surveying, the word ��shot�� is often be used. Some people use
the word ��leg.��
I understood your equations, so there was no problem there.
I wasn�_t quite sure what you meant by �� fast moving magnetic
interference�� and how you actually applied it in the field. I�_d be very
interesting in more information about how your technique works.
Larry
_____
From: [email protected] [mailto:[email protected]]
Sent: Tuesday, September 24, 2019 10:40 AM
Subject: RE: [compass-users] Magnetic Anomalies
......
Please forgive me for not good English.
I seem to confuse the two words ��wiress�� and ��line��.
Li Meng
���_EE: "compass-users";
��EIE�: 2019��9OA24EO(D��U_) �II�9:43
EO�_EE: "compass-users";
��I�: Re: RE: [compass-users] Magnetic Anomalies
hi
If it's really fast moving magnetic interference, I've used the following
two methods before:
1.Measure the relative Angle between two wires on a plane projection��
2.Use three sides of a triangle to calculate the Angle.
By measuring the three wires forming the triangle, calculate the side length
of the plane projection triangle and calculate the Angle.
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spf=pass [email protected];
dmarc=pass(p=none sp=NULL dis=none) header.from=qq.com;
Date: Fri, 27 Sep 2019 06:49:30 +0800
Feedback-ID: webmail:qq.com:bgweb:bgweb2
Subject: =?gb18030?B?u9i4tKO6UkU6IFtjb21wYXNzLXVzZXJzXSBNYWdu? =?gb18030?B?ZXRpYyBBbm9tYWxpZXM=?From: "=?gb18030?B?wO7DyC3Ez8POweE=?="
Larry��
Yes, the accumulation of errors is a problem.
Triangulation is only used locally in the special unstable magnetic fields.
I have never considered the problem of error accumulation in the past. Thanks for reminding.
Li Meng
------------------ O-E�OE�_ ------------------
���_EE: "compass-users";
��EIE�: 2019��9OA26EO(D��UE�) A�3�3:22
EO�_EE: "compass-users";
��I�: RE: [compass-users] Magnetic Anomalies
Li Meng,
This is a very interesting idea. If I understand what you are doing correctly, if you establish one shot with an accurate azimuth, you can then simply measure the distance between each end of the shot to a new station. This forms a triangle. Knowing the lengths of the sides of the triangle, allows you to calculate the azimuth angles in a way that completely avoids any magnetic anomalies.
This is similar to what land-surveyors with ��triangulation networks,�� except that they are measuring angles instead of lengths.
https://www.e-education.psu.edu/natureofgeoinfo/c5_p11.html
One issue with this method is the accumulation of errors. With the standard compass-tape-inclinometer method used by cave surveyors, the compass angle is re-referenced to magnetic north each time you take an azimuth reading. In other words, every time you take a compass reading, it is always relative the magnetic north. That means that the azimuth errors don�_t add up as you survey through a cave.
The same thing happens with the inclinometer readings. The inclination angle is always re-referenced to the Earth�_s gravity field, so errors don�_t add up.
With a land-survey, you measure angles between shots. As a result, an angle-error in the first shot is added to the error in the second shot and so on throughout the cave. This can add up to large errors at the end of the survey. For this reason, very accurate instruments (theodolites) and very accurate measurements are required.
The same thing could happen when measuring the sides of a triangle.. While tape measurements are probably more accurate than angle measurements, the errors would still add up and the calculated azimuth could be less accurate than similar measurements with a compass. That probably means the method is best used to deal with local magnetic anomalies. You probably wouldn�_t want to use it to cover large distances in the cave.
One advantage of the John Hallack�_s method is that doesn�_t really change the way you survey in the cave. Once you establish the base shot at the entrance, you just take normal fore and back sights. The difference comes when you process the data. Instead of just averaging the fore and back sights, you calculate the magnetic-anomaly at each station and use it to correct the azimuth for every shot that originates from that station.
Larry
From: [email protected] [mailto:[email protected]]
Sent: Wednesday, September 25, 2019 12:39 AM
To: compass-users
Subject: RE: [compass-users] Magnetic Anomalies
Larry��
I used the wrong word ��fast moving��......Rapid change, instability, periodic oscillation��
In guiyang, China, there is a cave with a hydroelectric power station
My specific implementation plan is:
For the distox2 scheme of triangulation.
Three people,One person as �� instrument person�� (A station), two people as�� front person �� (B, C station)The hole uses two gps to correct the magnetic field anomaly.
Start station A, measure A-B and A-C,
then move �� instrument person�� to B,
measure B-C,
repeat the process and advance. (A-B, A-C, B-C, B-D, C-D, C-E, D-E........)
(difficulty in Pit)
Need to pay attention to the left and right sides of the triangle.
After returning home, use the programmed program to calculate the azimuth uniformly.
The topodroid software also has a triangle loop closure, and the screenshot is a description of the topodroid.
Li Meng
---Original---
From: "'Larry' [email protected] [compass-users]"
Date: Wed, Sep 25, 2019 03:26 AM
To: "compass-users";
Subject: RE: [compass-users] Magnetic Anomalies
Li Meng,
Your English is fine. As a long-time learner of Spanish, I know how easy it is to get the subtle differences between different words right when you are working in a foreign language.
When I read your post, I assumed you meant ��line�� or ��shot�� when you said ��wire.��
In English, ��wire�� tends to refer to the long, round, thin metal things that are used to carry electricity. ��Line�� is a better choice. When referring to surveying, the word ��shot�� is often be used. Some people use the word ��leg.��
I understood your equations, so there was no problem there.
I wasn�_t quite sure what you meant by �� fast moving magnetic interference�� and how you actually applied it in the field. I�_d be very interesting in more information about how your technique works.
Larry
From: [email protected] [mailto:[email protected]]
Sent: Tuesday, September 24, 2019 10:40 AM
To: compass-users
Subject: RE: [compass-users] Magnetic Anomalies
......
Please forgive me for not good English.
I seem to confuse the two words ��wiress�� and ��line��.
Li Meng
------------------ O-E�OE�_ ------------------
���_EE: "compass-users";
��EIE�: 2019��9OA24EO(D��U_) �II�9:43
EO�_EE: "compass-users";
��I�: Re: RE: [compass-users] Magnetic Anomalies
hi
If it's really fast moving magnetic interference, I've used the following two methods before:
1.Measure the relative Angle between two wires on a plane projection��
2.Use three sides of a triangle to calculate the Angle.
By measuring the three wires forming the triangle, calculate the side length of the plane projection triangle and calculate the Angle.
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
Larry��Yes, the accumulation of errors is a problem.Triangulation is only used locally in the special unstable magnetic fields.I have never considered the problem of error accumulation in the past. Thanks for reminding.Li Meng------------------ O-E�OE�_ ------------------���_EE: "compass-users"<[email protected]>;��EIE�: 2019��9OA26EO(D��UE�) A�3�3:22EO�_EE: "compass-users"<[email protected]>;��I�: RE: [compass-users] Magnetic Anomalies
Li Meng,
This is a very interesting idea. If I understand what you are doing
correctly, if you establish one shot with an accurate azimuth, you can then simply
measure the distance between each end of the shot to a new station. This forms
a triangle. Knowing the lengths of the sides of the triangle, allows you to
calculate the azimuth angles in a way that completely avoids any magnetic
anomalies.
This is similar to what land-surveyors with ��triangulation networks,��
except that they are measuring angles instead of lengths.
https://www.e-education.psu.edu/natureofgeoinfo/c5_p11.html
One issue with this method is the accumulation of errors. With the
standard compass-tape-inclinometer method used by cave surveyors, the compass
angle is re-referenced to magnetic north each time you take an azimuth reading.
In other words, every time you take a compass reading, it is always relative
the magnetic north. That means that the azimuth errors don�_t add up as you
survey through a cave.
The same thing happens with the inclinometer readings. The inclination
angle is always re-referenced to the Earth�_s gravity field, so errors don�_t add
up.
With a land-survey, you measure angles between shots. As a result, an angle-error
in the first shot is added to the error in the second shot and so on throughout
the cave. This can add up to large errors at the end of the survey. For this
reason, very accurate instruments (theodolites) and very accurate measurements
are required.
The same thing could happen when measuring the sides of a triangle.. While
tape measurements are probably more accurate than angle measurements, the errors
would still add up and the calculated azimuth could be less accurate than
similar measurements with a compass. That probably means the method is best
used to deal with local magnetic anomalies. You probably wouldn�_t want to use
it to cover large distances in the cave.
One advantage of the John Hallack�_s method is that doesn�_t really
change the way you survey in the cave. Once you establish the base shot at the
entrance, you just take normal fore and back sights. The difference comes when
you process the data. Instead of just averaging the fore and back sights, you
calculate the magnetic-anomaly at each station and use it to correct the
azimuth for every shot that originates from that station.
Larry
From: [email protected] [mailto:[email protected]]
Sent: Wednesday, September 25,
2019 12:39 AM
To: compass-users
Subject: RE: [compass-users]
Magnetic Anomalies
Larry��
I used the wrong word ��fast moving��......Rapid change,
instability, periodic oscillation��
In guiyang, China, there is a cave with a
hydroelectric power station
My specific implementation plan is:
For the distox2 scheme of triangulation.
Three people,One person as �� instrument person�� (A
station), two people as�� front person �� (B, C station)The hole
uses two gps to correct the magnetic field anomaly.
Start station A, measure A-B and A-C,
then move �� instrument person�� to B,
measure B-C,
repeat the process and advance. (A-B, A-C, B-C, B-D, C-D, C-E,
D-E........)
(difficulty in Pit)
Need to pay attention to the left and right sides of the triangle.
After returning home, use the programmed program to calculate the
azimuth uniformly.
The topodroid software also has a triangle loop closure, and the
screenshot is a description of the topodroid.
Li Meng
---Original---
From: "'Larry' [email protected]
[compass-users]"<[email protected]>
Date: Wed, Sep 25, 2019 03:26 AM
To: "compass-users"<[email protected]>;
Subject: RE: [compass-users] Magnetic Anomalies
Li Meng,
Your English
is fine. As a long-time learner of Spanish, I know how easy it is to get the
subtle differences between different words right when you are working in a
foreign language.
When I read
your post, I assumed you meant ��line�� or ��shot�� when you said ��wire.��
In English,
��wire�� tends to refer to the long, round, thin metal things that are used to
carry electricity. ��Line�� is a better choice. When referring to surveying, the
word ��shot�� is often be used. Some people use the word ��leg.��
I understood
your equations, so there was no problem there.
I wasn�_t
quite sure what you meant by �� fast moving
magnetic interference�� and how you actually applied it in
the field. I�_d be very interesting in more information about how your technique
works.
Larry
From: [email protected]
[mailto:[email protected]]
Sent: Tuesday, September 24, 2019
10:40 AM
To: compass-users
Subject: RE: [compass-users]
Magnetic Anomalies
......
Please forgive me
for not good English.
I seem to confuse
the two words ��wiress�� and ��line��.
Li Meng
------------------
O-E�OE�_ ------------------
���_EE: "compass-users"<[email protected]>;
��EIE�: 2019��9OA24EO(D��U_) �II�9:43
EO�_EE: "compass-users"<[email protected]>;
��I�: Re: RE: [compass-users] Magnetic
Anomalies
hi
If it's really
fast moving magnetic interference, I've used the following two methods before:
1.Measure the
relative Angle between two wires on a plane projection��
2.Use three sides
of a triangle to calculate the Angle.
By measuring the
three wires forming the triangle, calculate the side length of the plane
projection triangle and calculate the Angle.
Authentication-Results: mta4002.groups.mail.ne1.yahoo.com; dkim=pass (ok) [email protected] header.s1hai; spf=pass [email protected]; dmarc=pass(p=quarantine sp=NULL dis=none) header.from=mac.com; Date: Fri, 27 Sep 2019 08:00:59 +0200 Subject: =?utf-8?Q?Re:_�>z�?��sRE:_[compass-users]_Mag? =?utf-8?Q?netic_Anomalies?From: Martin Sluka Anyway with two DistoXs triangulation is very easy. Martin OdeslA�no z iPhonu 27. 9. 2019 v 0:49, '�?Z�?O-�?-��݇Z�' [email protected] [compass-users] : Larry��s Yes, the accumulation of errors is a problem. Triangulation is only used locally in the special unstable magnetic fields. I have never considered the problem of error accumulation in the past. Thanks for reminding. Li Meng ------------------ �ZY�<�,r�� ------------------ �?`�����: "compass-users"; �?`�??�-�-': 2019�1'9�o^26�-�(�~Y�oY�>>) ��O�T"3:22 �"�����: "compass-users"; �,���~: RE: [compass-users] Magnetic Anomalies Li Meng, This is a very interesting idea. If I understand what you are doing correctly, if you establish one shot with an accurate azimuth, you can then simply measure the distance between each end of the shot to a new station. This forms a triangle. Knowing the lengths of the sides of the triangle, allows you to calculate the azimuth angles in a way that completely avoids any magnetic anomalies. This is similar to what land-surveyors with �?otriangulation networks,�?? except that they are measuring angles instead of lengths. https://www.e-education.psu.edu/natureofgeoinfo/c5_p11.html One issue with this method is the accumulation of errors. With the standard compass-tape-inclinometer method used by cave surveyors, the compass angle is re-referenced to magnetic north each time you take an azimuth reading. In other words, every time you take a compass reading, it is always relative the magnetic north. That means that the azimuth errors don�?Tt add up as you survey through a cave. The same thing happens with the inclinometer readings. The inclination angle is always re-referenced to the Earth�?Ts gravity field, so errors don�?Tt add up. With a land-survey, you measure angles between shots. As a result, an angle-error in the first shot is added to the error in the second shot and so on throughout the cave. This can add up to large errors at the end of the survey. For this reason, very accurate instruments (theodolites) and very accurate measurements are required. The same thing could happen when measuring the sides of a triangle.. While tape measurements are probably more accurate than angle measurements, the errors would still add up and the calculated azimuth could be less accurate than similar measurements with a compass. That probably means the method is best used to deal with local magnetic anomalies. You probably wouldn�?Tt want to use it to cover large distances in the cave. One advantage of the John Hallack�?Ts method is that doesn�?Tt really change the way you survey in the cave. Once you establish the base shot at the entrance, you just take normal fore and back sights. The difference comes when you process the data. Instead of just averaging the fore and back sights, you calculate the magnetic-anomaly at each station and use it to correct the azimuth for every shot that originates from that station. Larry From: [email protected] [mailto:[email protected]] Sent: Wednesday, September 25, 2019 12:39 AM To: compass-users Subject: RE: [compass-users] Magnetic Anomalies Larry��s I used the wrong word �?ofast moving�??......Rapid change, instability, periodic oscillationa?, In guiyang, China, there is a cave with a hydroelectric power station My specific implementation plan is: For the distox2 scheme of triangulation. Three people,One person as �?o instrument person�?? (A station), two people as�?o front person �?? (B, C station)The hole uses two gps to correct the magnetic field anomaly. Start station A, measure A-B and A-C, then move �?o instrument person�?? to B, measure B-C, repeat the process and advance. (A-B, A-C, B-C, B-D, C-D, C-E, D-E........) (difficulty in Pit) Need to pay attention to the left and right sides of the triangle. After returning home, use the programmed program to calculate the azimuth uniformly. The topodroid software also has a triangle loop closure, and the screenshot is a description of the topodroid. Li Meng ---Original--- From: "'Larry' [email protected] [compass-users]" Date: Wed, Sep 25, 2019 03:26 AM To: "compass-users"; Subject: RE: [compass-users] Magnetic Anomalies Li Meng, Your English is fine. As a long-time learner of Spanish, I know how easy it is to get the subtle differences between different words right when you are working in a foreign language. When I read your post, I assumed you meant �?oline�?? or �?oshot�?? when you said �?owire.�?? In English, �?owire�?? tends to refer to the long, round, thin metal things that are used to carry electricity. �?oLine�?? is a better choice. When referring to surveying, the word �?oshot�?? is often be used. Some people use the word �?oleg.�?? I understood your equations, so there was no problem there. I wasn�?Tt quite sure what you meant by �?o fast moving magnetic interference�?? and how you actually applied it in the field. I�?Td be very interesting in more information about how your technique works. Larry From: [email protected] [mailto:[email protected]] Sent: Tuesday, September 24, 2019 10:40 AM To: compass-users Subject: RE: [compass-users] Magnetic Anomalies ...... Please forgive me for not good English. I seem to confuse the two words �?owiress�?? and �?oline�??. Li Meng ------------------ �ZY�<�,r�� ------------------ �?`�����: "compass-users"; �?`�??�-�-': 2019�1'9�o^24�-�(�~Y�oY��O) �,S�?^9:43 �"�����: "compass-users"; �,���~: Re: RE: [compass-users] Magnetic Anomalies hi If it's really fast moving magnetic interference, I've used the following two methods before: 1.Measure the relative Angle between two wires on a plane projectiona?, 2.Use three sides of a triangle to calculate the Angle. By measuring the three wires forming the triangle, calculate the side length of the plane projection triangle and calculate the Angle. Anyway with two DistoXs triangulation is very easy. MartinOdeslA�no z iPhonu27. 9. 2019 v 0:49, '�?Z�?O-�?-��݇Z�' [email protected] [compass-users] <[email protected]>: