[gdal-dev] gdalwarp interpolation artifacts

[Frank Warmerdam]

On Tue, Sep 30, 2008 at 4:30 AM, Roger André <randre at gmail.com> wrote:
> Hi List,
>
> I've hit the same problem twice now, and I'm pretty certain after Round 2
> that I'm not introducing it.  Basically, I'm using gdal_merge.py to mosaic a
> group of low-resolution, 32-bit floating point rasters together, then
> running "gdalwarp -ts xxx yyy -r cubicspline" on the mosaic to get a higher
> resolution image.  I'm finding afterwards that there are linear artifacts in
> the mosaic which run vertically through the mosaic, which look like edge
> artifacts, but which are not located near the edge of either an original
> low-res tile, or the resulting high res one.  I've tested the interpolation
> of a single low-res tile in the area where the artifact is present in the
> mosaic and I do not get the same results - the interpolated tile is clear of
> artifacts.
>
> Is it possible that I'm hitting some sort of memory limit that is causing
> only a certain number of columns to be interpolated at one time, rather than
> the entire row?

Roger,

There have been some fixes to some of the gdalwarp interpolator
code in recent months, so one hint is to ensure you try the latest
"trunk" code to see if perhaps the problem is already fixed.

Second, you may want to investigate the gdal_merge.py product
carefully to ensure there aren't any bad pixels in it along the
boundaries.

Third you might try the cubic (instead of cubicspline) interpolator
to see if it gives cleaner results.

Beyond that a ticket submitted on the smallest test case that
demonstrates the problem would be appreciated.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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