Some of us need to export the LAS point cloud to Civil 3D back to local coordinates, since all our CAD files are local not state plane.
For example the local coordinate system from my planset is:
Northing Conversion: 2624946.571 (local to state plane)
Easting Conversion: 1312508.894 (local to state plane)
When I use those factors with my GCP’s they are where I expect them to on the Pix4d map and I’m able to use the basic GCP editor. Since the drone captures everything in state plane this is all fine and well for the processing. My problem is the output of the LAS (which I want to import into Civil 3D), I manually enter the site calibration in Pix4d but the results don’t make sense.
I tried use the following in the site calibration:
Northing Conversion: -2624946.571 (difference from state plane to local)
Easting Conversion: -1312508.894 (difference from state plane to local)
Scale: 1.000100964 (inverse from original scale)
But the math doesn’t work, going back from state plane to local requires the inverse scale to be multiplied then the Transform be added/subtracted.
I believePix4d assumes the following;
(State Plane Northing or Easting + Northing or Easting Transform)*Scale=Local Coordinates, This is what I use to transform the GCP’s to state plane for processing.
but to transform back to local from state plane I need;
(Local Coordinates*inverse scale)-Northing/Easting Transform, so I can import the LAS into Civil 3D.
I suppose the *fix is to edit the EXIF data in the drone photos prior to processing, not modify the GCP’s, and not display a background map thus processing everything in the local coordinates.