[gdal-dev] GDAL Warp API : Transforms on Z

[Adam Stambler]

Hi All,

I am trying to implement a warp from a latitude, longitude, altitude (LLA)
image into a custom coordinate system using the GDAL Warp API.  The
transform between LLA and my coordinate requires scaling and shifting the
elevation.  My coordinate system is  a local tangent plane on the Earth's
surface where x is north, y is east, and z is pointed into the Earth.

When I follow the instructions in the GDAL Warp API tutorial
<http://www.gdal.org/warptut.html>,  my custom transform function supplied
to "psWarpOptions->pTransformerArg
<http://www.gdal.org/structGDALWarpOptions.html#a35647845a2629da876f379f82d58a2cd>"
only receives input z=0 values.  From the source code, it looks like the
internal GDALWarpKernel only passes z=0 values to to the pTransformerArg.
The Z values from the source elevation map are never used and therefore can
never be re-projected.

How can GDAL properly transform the source elevation data if the source
elevation is never passed to the transform function?

 How are transforms between ellipsoids or elevation units performed if not
through the GDALWarpOperation
<http://www.gdal.org/classGDALWarpOperation.html> API?


Thank you for any insights.

-Adam Stambler
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