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We have a Trimble unit we use to collect equipment.

We collect the data in WGS84 and differentially correct it and then reproject it to a state plan coordinate system.

The points always shift the same distance in the same direction after the reprojection.

What is the reason for this?


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closed as unclear what you're asking by PolyGeo, BradHards, Simbamangu, Chad Cooper, Paul Nov 24 '13 at 4:59

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question.If this question can be reworded to fit the rules in the help center, please edit the question.

Are you applying the appropriate transformation? – johns May 2 '13 at 14:38
The default transformations are not the best one. Select the one meant for your area. Here is how you find which is the best one:… – Devdatta Tengshe May 2 '13 at 16:17
Which state plane coord system? – Kirk Kuykendall May 2 '13 at 21:05
Can you perhaps specify which State Plane Coordinate System you are using and include a screenshot of the Transformation that you chose to use with it? – PolyGeo Nov 23 '13 at 21:09
up vote 2 down vote accepted

It may be a lack of datum transformation in your projection operation.

Your symptom sounds familiar. It is a common problem here in Wisconsin - GPS uses the WGS84 datum, but our state system uses NAD83HARN.

The symptom of doing a projection without datum transformation is that coordinates are systematically offset a few meters in X and ~meter in Y.

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