[gdal-dev] gdalwarp interpolation artifacts

[Seth Price]

I agree with Frank, this sounds like the bug that I reported (and  
fixed) here:
http://trac.osgeo.org/gdal/ticket/2327

(Although it became a log of my alterations to the warper kernel,  
which was well beyond the scope of the original bug.)
~Seth


On Sep 29, 2008, at 11:19 PM, Frank Warmerdam wrote:

> 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,
> -- 
> --------------------------------------- 
> +--------------------------------------
> 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    | Geospatial Programmer for  
> Rent
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