Topcon .gc3 files with propeller

Lots of questions.

Why do you want ground?

How did you localize?

Did you get any static data?

Why are you not using grid?

What are they comparing the coordinates too?

?ÿ

Hi Lee,

(1) I would like the aerial map / contours in local ground coordinates, because we do boundary surveys in local grid. I could then bring the photo or contours into my boundary drawing (I use TraversePC and Carlson).

(2) As for coordinates, we generally start our work in State Plane Coordinates, either autonomous or we locate a couple NGS control points to get on true SPCS. Then we would figure a grid-to-ground correction using parameters at one point and for azimuth use either geodetic or the record azimuth between found monuments.

(3) The problem I am having with Propeller is that, in order for it to compute grid-to-ground correction, it needs either a Trimble .jxl file or a Topcon .gc3 file. I got someone to make a .jxl file for me and it worked fine. However, I have not been able to make the .gc3 file work in Propeller. When I make a .gc3 file using Topcon 3D Office, I use three control points, providing latitude / longitude and local coordinates for each point. I then put that file into Propeller. I then have to hand-enter the grid-to-ground parameters from 3D Office into Propeller and provide latitude / longitude and ground coordinates for a check point. Propeller then compares it's calculated ground coordinates for the check point with the coordinates I provide. Propeller says there is about 0.5 feet difference between the two, SO, it will not set up the ground system.

Sounds like you are using L1 GPS, since you don't mention OPUS? What GPS recievers are you using? What procedures to get coordinates, static, rtk, rtn?

Is the 0.5ft error in horizontal or vertical?

You mention grid to ground. You likely would never notice the difference between grid and ground in a drone survey, just can't get that accuracy, and projects not large enough to see 1:10000. Unless you are a some extreme?ÿ elevation which will effect the CSF.

You describe azimuth corrections.?ÿ Are you only concerned with basis of bearings?

What is the deliverable in your CAD?

Why not process in grid, then use CAD or [REDACTED] for reprojection to Geodetic bearings and ground??ÿ

How did you create the GC3?

The drone software Propeller is trying to extract the Geographic coordinates (Lat/Lon/Ell ht) from the GC3, to build the projection to the ground Cartesian coordinates.?ÿ Send me the GC3 file, the ground coordinates and the Lat/Long/Ellisp Ht you feel is correct for each point. I can see if they were correctly entered in the GC3. Then check the localization for errors.

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