Good afternoon,
First of all, I am not a surveyor, I am just helping out on a project.
I had a GPS base station set up on a previous base station location and it ran for about 5 hours. It also had a radio. We collected three points within the project area using RTK. I got an OPUS solution for the base, corrected the base location to the OPUS solution and then and post processed the RTK. I checked the locations on a high resolution aerial image and they are correct.
Then we set up the Total Station over the same base location and entered the base station location for that point. We then visited the same three points with a FC-500 handheld controller that talks to the total station. Our resulting data has an offset. The base is fine but the three points are rotated ~20å¡ west of where they should be. If I use the base as the pivot point, I can rotate them and get them to sit exactly on top of the same points that were surveyed with GPS.
I am sure I am glossing over all of the details you need to know to help me troubleshoot this, but does anyone have any idea of where I need to look in my setup to get rid of this offset?
Thank you for your time.
CMBernier
A total station needs to be oriented somehow for direction. It measures angles between the things sighted, not absolute directions. What did you use for a backsight (ie/ reference)? If it was nothing, we have identified your problem.
OK. Thank you. There was some back sight measurement but it was very confusing to me and did not seem to tie in to the base or any other known point so I am sure you are right.
So when I go back out there, if I setup the total station on one of the three GPS points, say CP1 and manually enter corrected coordinates for that point and then go to the Base Station Location with the handheld and enter those coordinates manually and then tell it that is the back sight, will I then be able to get the other two points collected accurately? Am I doing that backwards? Will all of the measurements from then on be angles and distances from the Base Station location or from CP1? We probably WILL set up the Total station at CP1 because there is a building that restricts the line of sight between the Base station location and some of the project area and we didn't want the total station to lose the prism behind the building.
Thank you for your help.
Yes, you have to orient your total station to at least two known points. Also you should set up the job in the controller with the correct information for the projection you are using. If you are using state plane coordinates from the OPUS solution then that should be in the library on the controller.
