[Gdal-dev] Warping image...

[Frank Warmerdam]

Mario Cavicchi wrote:
> Hi all,
> I have a little problem with a modis image, i must to reproject it in 
> UTM meter. I use the function GDALCreateWarpOperation and i must to set 
> nOrder = 3. The output image is correct, but the left and right sides 
> are wrong.
> I don't able to explain where is the problem, but the result is this
> http://members.ferrara.linux.it/cavicchi/tmp/modis.jpg

Mario,

It has been my experience that 3rd order polynomials can easily do some
pretty odd things.  I assume what you are seeing is some sort of "wrap
back on itself" property of the polynomials that were computed.  I'm not
clear on whether this is a defect of the computations done in GDAL or
whether it is inherent in a best fit for the control points available.

Generally speaking I just avoid polynomials of order higher than 2, or
sometimes I will try the thin plate spline (-tps) option.

It would have been helpful in reviewing your problem to have the a pointer
to the input file.  It is always possible there is something really funky
about the control points, but we don't have much to work with to figure that
out.

Best regards,
-- 
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