Geographic Calculator Overivew

The Calculator is used in three different ways. First, it is used to enter fixed stations locations. Second, it can be used as a stand-alone calculator for converting coordinates between different systems. Finally, it can be used to calculate the magnetic declination for a particular survey.

1. Calculating Base Locations. One important use of the Geographic Editor/Calculator is set the Base Location of a project. The Base Location is used to specify the general location of cave or cave system. It used for things such as calculating the magnetic declination.

2. Calculating Fixed Station Locations. Another important use of the Geographic Editor/Calculator is to enter or edit values for Fixed Stations. To do this, you must be working with a Project and you must highlight one of the surveys in the Survey Tree. Once you have highlighted one of the surveys, press the Edit Node button. Finally, select the "Links Page", check the "Use UTM" check box and press the "Geographic Reference" button. Once you have made your calculations, you can use them to set the location of the station by clicking on the "OK" button. If you click on the "Cancel" button, the new value will not be used. (See the “Doing Calculations” section below for detailed information about using the Calculator.)

Calculating UTM Convergence Angles. You can also use the Geographic Calculator to calculate the UTM Convergence angle. This angle is used to rotate the cave to match the local UTM grid. To do this, you must be working with a Project and you must highlight one of the surveys in the Survey Tree. Once you have highlighted one of the surveys, press the Edit Node button. Finally, select the "Links Page", check the "Use Convergence" check box and press the "Geographic Reference" button. Once you have made your calculations, you can use them to set the Convergence Angle by clicking on the "OK" button. If you click on the "Cancel" button, the new Convergence value will not be used. See the “Doing Calculations” section below for detailed information about using the Calculator.) Click here for more detailed information about Convergence.

3. Using Geographic Calculator Stand-Alone. To run the Geographic Editor as stand-alone tool, select the "Tools|Geographic Editor/Calculator" option from the menu bar.

Doing Calculations. The Geographic Editor/Calculator is divided into two main sections. The top half handles Longitude and Latitude and the bottom half handles UTM. If you are working with Longitude and Latitude, you simply enter or read values in the boxes at the top. If you are working with UTM, you enter or read values from the bottom.

Converting Data. As you enter a location in either Longitude/Latitude or UTM, the program automatically converts it to the other value.  This makes it easy to convert from one unit to another.

Converting Between Different Datum. It is sometimes useful to convert Longitude and Latitude measurements from one datum to another. To do this, first make sure the “Enable Datum Conversion” checkbox is enabled.  Next, simply select a different datum. The program will automatically convert the coordinates to the new datum. Click here for more information about converting between different Datum.

4. Calculating Declination. Magnetic Declination is the difference between true north and magnetic north. Since cavers usually survey with magnetic compasses, declination effects the accuracy of cave surveys. This especially true for caves that are surveyed over a long period of time since declination changes over time. This can cause severe loop closure errors between survey that were done at different times. Click here for more detailed information about Declination.

As a result of this problem, the Geographic Calculator allows you to calculate the magnetic declination for a particular location and date. Because of the fact that the declination is calculated for a precise time and date, it can be much more accurate that the usual methods such as reading it off a map.