Closing Loops With Fixed Stations

Compass allows you to create fixed survey stations. Fixed survey stations are stations whose location is anchored to preset coordinates. Fixed stations effect the way the loop closer closes loops. If you have one fixed station, there is no effect on the loop closing process. If there is a loop in a cave with one fixed station, the loop just becomes anchored to the fixed station.

If you have two or more fixed stations, the fixed stations change the way loops are closed. They "lock-down" the ends of survey lines and create artificial loops. As an example, let’s say you had two shots: A1->A2 and A2->A3. If A1 and A3 are tied to fixed locations, then you have, in effect, an artificial loop. The loop closer will then adjust this loop making sure that the fixed stations do not move. This will have the effect of distributing all errors between the two fixed stations. (Note: Since fixed stations are defined in Project files, you have to create and use a project file before the loop closer will use fixed stations.)