Posted by:Michael Draper


If anyone could help out here it would be much appreciated.

I have a project that was established via Trimble GPS utilizing the 2012A Geoid Model.  We broke down a section utilizing a new No Projection/No Datum project in the TSC2. The above stated geoid model was used along with a mean project height to derive the ground scale factor for our local area.

Once we'd verified that the measured baselines were consistent with historical measurements in the section a 2 point (horizontal only-H scale fixed to 1) calibration was applied to a chosen section line to align the measurements  with the local historical bearing structure.

After the project was established, coordinates for a control line (with a fixed distance) were entered with elevations of 0 and both ends of the control line were monumented using these coordinates.

I am now trying to utilize the control line for a total station traverse using a Sokkia Set 30R and the station setup residual is almost 2 tenths different (in 800') than the GPS measured baseline length.  As soon as I perform the backsight opperation using the coordinates with an elevation of 0 everything works fine and the total station measurements appear to be fine.

Any help would be great.


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