[Gdal-dev] gdalwarp: target image extents are recognised wrong

[Frank Warmerdam]

Michael84 wrote:
> Hello,
> 
> I'm using gdalwarp to warp an image of 15862P x 19548L from UTM to Lat/Long.
> 
> gdalwarp -s_srs "+proj=UTM +zone=32 +datum=WGS84" -t_srs "+proj=latlong
> +datum=WGS84" utm.tif latlong.tif
> 
> Gdalwarp then creates an image of 20491P x 15138L, instead of 15862P x
> 19548L or something with the same apect ratio!!! What could be the reason
> for it ?
> 
> I know that providing the target size is one solution to this problem, but
> it is not quite nice...

Michael,

If the region is large, my guess would be that the aspect ratio of your
region is quite different in lat/long (ie. Plate Carree) than it is in
UTM.  Even a small region relatively near the pole can exhibit substantial
changes in aspect ratio in such a transformation.

Best regards,
-- 
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