[gdal-dev] gdalwarp trunk and FWtools giving different results

[Frank Warmerdam]

Joaquim Luis wrote:
> Testing with RC2 shows that the wrong result persists like with the 
> trunk version.
> 
> with a small variation now
> gdalwarp -s_srs "+proj=merc +R=6371008.7714" -t_srs "+proj=latlong 
> +datum=WGS84" alg.tiff alg_geo.tiff
> 
> I have put the file at
> ftp.ualg.pt/users/jluis/alg.tiff
> 
> Shell I file a ticket saying that gdalwarp is broken when converting 
> from Mercator?

Joaquim,

I suspect the problem is that your source coordinate system has no
defined earth model that OGRSpatialReference understands.  Is the
+R parameter defining the radius for a spherical earth?

If so, you could file a ticket asking that
OGRSpatialReference::importFromProj4() be improved to support this
parameter. But the work around is to just define the sphere with
+a and +b which are supported.

-s_srs "+proj=merc +a=6371008.7714 +b=6371008.7714"

Or perhaps I'm on the wrong track, in which case a ticket would also
be a good idea.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | President OSGeo, http://osgeo.org