[gdal-dev] 3D transformation of DSM

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[gdal-dev] 3D transformation of DSM

Aurelien Vila
Hello All, 

I have to transform a DSM from a local CRS such as those produced by the trimble site calibration process ( : https://help.trimblegeospatial.com/TrimbleAccess/2018.10/en/Calibration.htm), to WGS84 ellipsoidal coordinates.  
The local CRS is defined by a projection (in this case transverse mercator) plus vertical and horizontal adjustment. Horizontal adjustment is a 2D similarity and thus can be described with a 2D Helmert transform. Vertical adjustement is a geoid model in the form of an inclined plane thus it could be described using an affine transform.
I have written a proj pipeline able to realize this transformation. It works great for vector file transformations (thanks to the new GDAL 3 release) but it doesn't work for DSM transformation since the affine transform step used for the vertical adjustment seems to be not supported by gdalwarp (the pixels values stay unchanged). 
I guess that gdalwarp only support vertical grid shift to handle pixel value modifications, but anybody can confirm me this ? 
If no, which method can accomplish this DSM transformation ? If yes, do you plan to support other 3D transformation with gdalwarp at short or mid terms ? 

Best regards

Aurélien Vila
Computer Vision Engineer

676, Rue Max Planck – 31670 Labège - FRANCE
Tel+33 9 71 16 99 01


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