[gdal-dev] Warping with modified source geotransform

[Brian Claywell]

Our image-to-image coregistration process produces an affine 
transformation matrix that specifies the pixel-space transformation 
necessary to transform the image B to match image A. Since a 
geotransform is just an affine pixel-space transformation, the original 
  image B geotransform can be combined with the coregistration 
transformation by matrix multiplication to yield a new image B 
geotransform. However, the new image B geotransform is not guaranteed to 
be north-up, so the image B (with its modified geotransform) needs to be 
warped into a north-up image, and to compute those parameters I've used 
the GDALSuggestedWarpOutput() function.

But I've run into a bit of a roadblock. The GDALGenImgProjTransformer 
and GDALSuggestedWarpOutput() both read the source geotransform directly 
from the source dataset, but I want to inject the modified source 
geotransform as described in the above paragraph. Unfortunately, as best 
I can tell, it's near impossible to modify the source geotransform of a 
GDALGenImgProjTransformer, because the struct definition for 
GDALGenImgProjTransformInfo is hidden away inside 
alg/gdaltransformer.cpp, so one can't cast from void* to 
GDALGenImgProjTransformInfo* to get at the adfSrcGeoTransform member (at 
least without replicating the struct definition in my own code, but I'd 
really rather avoid breaking GDAL's encapsulation there :) ).

Can anyone think of a way to accomplish this? Or is there a better way 
to do this that I haven't thought of?

Thanks!

-b

--
Brian Claywell
brian.claywell at gmail.com