Local Coordinate transform

PIX4Dmapper PIX4Dmapper Questions/Troubleshooting
1

Hello,

I’m trying to export the LAS point cloud to Civil 3D but the output coordinate system from Pix4D is not where I’m expecting it to be.  The local coordinate system from the planset is:

Northing Conversion: 2624946.571 (local to state plane)

Easting Conversion: 1312508.894 (local to state plane)

Scale: 0.999899046

 

When I use those factors and adjust my GCP they line up 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, I manually enter them into the site calibration in Pix4d but the results don’t make sense.  

 

I 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)

 

I’m sure I have made a mistake somewhere since the point clouds are not falling within my project in Civil 3D.  Any help would be appreciated.  

 

-Ryan

 

2

Found the problem, going back from state plane to local requires the inverse scale to be multiplied then the Transform be added/subtracted.  I imagine Pix4d assumes

(State Plane Northing or Easting + Northing or Easting Transform)*Scale=Local Coordinates, This is what I use for the GCP while 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 the edit the EXIF data in the drone photos and convert them to local coordinates prior and ignore the map coordinates in pix4d while processing.