[Gdal-dev] GDALWarp Gif Problems

Frank Warmerdam warmerdam at pobox.com
Tue Jan 23 15:16:49 EST 2007

Chris Portka wrote:
> Thanks for your feedback.  I think I may have narrowed down the problem, 
> but I'm confused on one point that I can't find documentation for.  In 
> the warp tutorial there is the following line for getting the suggested 
> output:
> eErr = GDALSuggestedWarpOutput 
> <http://gdal.org/gdal__alg_8h.html#816819e7495bfce06dbd110f7c57af65>( 
> hSrcDS,                                    GDALGenImgProjTransform, 
> hTransformArg,                                    adfDstGeoTransform, 
> &nPixels, &nLines );
> I understand what all these arguments are except 
> GDALGenImgProjTransform, which I believe to be the transformer 
> function's signature, but I'm unclear.  Where is this defined?  How does 
> this interact or differ from hTransformArg?  I'm pretty sure it is 
> something to do with this interaction that is acting funny.  Are there 
> alternatives to this such as a GDALReprojectionTransform?  Is there a 
> list of all possible alternatives or a way to construct one myself?  


The transformer is an actual function while the transformarg is the
private data used by the transformer to keep track of what it is
supposed to do.  The GDALTransformerFunc concept is documented at:


You can also get there by following the GDALTransformerFunc link from the
GDALSuggestedWarpOutput() documentation you referenced.

You can implement your own transformation function though that should
rarely be needed.  The GDALTransformFunc docs list some of the common
implementations.  But for your case you will presumably want to use

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org

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