[gdal-dev] Remove Black Areas From Rotated Images

[M Lewis]

I have searched and found lots of similar queries but nothing that quite
gives me the answer that I am looking for (as they all appear to be related
to gdal_translate rather than the C++ API.)

We have a set of strips of grey scale satellite imagery that are rotated.

I use AutoCreateWarpedVRT to generate a 'north-up' image that is converted
to a bitmap and displayed to the user.
When displayed the image has a black area surrounding it which tends to mask
other images that tile alongside.

>From searching around I assume it is to do with the GDALWarpOptions that can
be passed to the AutoCreateWarpedVRT function but the 'no-data' value of the
dataset when queried fails and just returns a default of -10000.0. 
Therefore I am unsure of what to set in the padfDstNoDataReal etc variables
to mask out the areas where there is no data.

The image is grey scale, the 'non-data' areas come out as black once the
image is returned from the RasterIO call so it makes it difficult to
post-process the image data.

Anybody got any tips on the way to do this and maybe set up the
GDALWarpOptions to pass to the AutoCreateWarpedVRT function? 
Is it even possible on a grey-scale dataset with no 'no-data' value?

Thanks

Martin




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