[Gdal-dev] gdalwarp reprojection not exact

[Frank Warmerdam]

lBert wrote:
> Hi,
> 
> I've been trying to reproject an orthophoto (1-m resolution) using gdalwarp
> (gdal 1.5), but the results are not very satisfying (see below). I overlaid
> the reprojected image with the input image and at the first look the results
> seemed fine, but when I zoomed in, I realized that the reprojected image is
> quite distorted. Since the distortion occurs in these blocky patterns
> (blocks of ~30x30 pixels) I assume that this is the result of gdal using
> some linear approximation. Now, I have tried changing several options, also
> setting the -te switch to 0.0, but the results are always the same. Of
> course when I use cubic convolution the effect is not as pronounced, but it
> is still there. I played around with this the whole day and I can't find a
> solution. ArcGIS and Erdas Imagine produce good results even with polynomial
> approximation. 
> Please help!
> 
> Here is an animated gif comparing the input and reprojected image:
> http://www.nabble.com/file/p17267217/gdalwarp_input_output.gif
> gdalwarp_input_output.gif  

Bert,

Can you provide the source data?  Gdalwarp does not chunk things in 30 x 30
pixel chunks (normally chunks are roughly 2Kx2K) so I don't believe this is
an artifact related to the chunking logic.

Best regards,
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