[gdal-dev] GDAL Arbitrary Warp Problems

[Michael Aschenbeck]

Thanks for your response.

For my application, I will be creating the transformation on the fly.  It
will be a non-standard transformation.  Unless I'm mistaken, I don't
believe this can be done with gdalwarp directly.

Also, I am under the assumption that its source code is introduced in the
tutorial I am working off of (http://www.gdal.org/warptut.html).  Yet, this
just introduces a standard transformation, not a custom one.  This is why
I'm having trouble.

Thanks,
Mike


On Tue, Jul 15, 2014 at 12:43 PM, Even Rouault <even.rouault at mines-paris.org
> wrote:

> Le mardi 15 juillet 2014 20:33:32, Michael Aschenbeck a écrit :
> > Hello,
> >
> > I'm trying to follow the warp tutorial (http://www.gdal.org/warptut.html
> )
> > to do a general warp.  However, I'm not getting any good results.
> >
> > I first recreated the example in the warp tutorial by first implementing
> > the bottom portion modified to output an RGB image, then implementing the
> > top portion with GDALGenImgProjTransform as written.  This worked fine.
> >
> > Second, I tried to create my own, most basic, transformation:
> >
> > int identityTransform(void *pTransformerArg,int bDstToSrc, int
> nPointCount,
> > double *x, double *y, double *z, int *panSuccess)
> > {
> > return 1;
> > }
> >
> > i.e. it does not modify any coordinates.  So I changed:
> > eErr = GDALSuggestedWarpOutput( poDataset, GDALGenImgProjTransform,
> > hTransformArg, adfDstGeoTransform, &nPixels, &nLines );
> > to:
> > GDALTransformerFunc myTransformer = &identityTransform;
> > eErr = GDALSuggestedWarpOutput( poDataset, myTransformer, hTransformArg,
> > adfDstGeoTransform, &nPixels, &nLines );
> >
> >
> > and
> > //psWarpOptions->pfnTransformer = GDALGenImgProjTransform;
> > to:
> >          psWarpOptions->pfnTransformer = myTransformer;
> >
> > I expect to get the same image back but all i get is two vertical lines
> > with unreasonable georeferenced coordinates.  I'm hoping someone can show
> > me where I'm going wrong, or guide me to an example of a custom
> > GDALTransformerFunc to use as a template.
> >
> > Thank you in advance for any help you can give!
>
> Why not using gdalwarp directly, or re-using its source code ?
>
> --
> Geospatial professional services
> http://even.rouault.free.fr/services.html
>
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