[gdal-dev] problems with gdal_merge.py

Frank Warmerdam warmerdam at pobox.com
Tue Apr 22 13:50:42 EDT 2008

Volker Wichmann wrote:
> Hi,
> I'm checking gdal_merge.py for generating subsets and mosaics from one 
> or more input rasters. I found the following problem using esri ascii 
> grids as input:
> In case of the ascii, the file is resampled (and thus the values in the 
> output subset differ from the original). This doesn't happen with a 
> geotiff as input (see the "Copy" lines above).
> It's also strange, that in both cases the reported UL and LR don't match 
> the input coordinates and the extent of the output files (the latter 
> match the coordinates passed with -ul_lr).
> I'm still using GDAL but haven't found any major changes in trac 
> regarding gdal_merge.py. It would be nice if somebody could try to 
> reproduce this with GDAL 1.5 to see if any of the underlying functions 
> have changed.


I believe there have been some problems with "off by a half pixel" issues
in the ESRI ASCII Grid driver since 1.4.2.  I would suggest upgrading to
1.5.1 if you can.   If the issue persists file a detailed ticket on it.

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    | President OSGeo, http://osgeo.org

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