[gdal-dev] gdalwarp cutting off projected image

Scott Lewis scott.lewis at nsidc.org
Wed Dec 10 11:27:04 EST 2008

Frank Warmerdam wrote:
> Scott Lewis wrote:
>> Frank,
>> The image I've been trying to convert is at this URL.  It's about 
>> 6MB, hopefully that's not too big.
>> ftp://sidads.colorado.edu/pub/incoming/glewis/polar.gtiff.tif
>> Basically, I'm trying to convert it to a plain-old EPGS:4326 (latlong 
>> projection).
>> I appreciate you taking a look.
> Scott,
> I have established the problem is the logic that computes the desired
> extent of the output file.  It walks the edges of the input file,
> transforming to WGS84 and ends up with incomplete extents because there
> is no recognition that there is a topological discontinuity in the
> transformation (the pole issue).
> Normally my advice would be to use the SAMPLE_GRID=YES warp option to
> force internal sampling of the region when computing the bounds, but
> I have discovered that only applies to deciding what source region
> to read during warping - not to the computation of the original warp
> region.
> So, in the meantime you can just force selection of output extents.
> Something like:
> gdalwarp -t_srs EPSG:4326 polar.gtiff.tif out.tif -te -180 28 180 90
> When I have the ticket in hand, I'll plan to modify the
> GDALSuggestedWarpOutput() function to allow forcing of internal gridding.
> It would also be nice if I could automatically recognise this sort of
> case to trigger it automatically, but I'm not sure how to do that
> without quite a bit of extra work.
>> PS - I'm still new to the GDAL list; when you say file a Trac ticket, 
>> where would I do this?
> Visit:
>  http://trac.osgeo.org/gdal
> There should be brief instructions on getting an OSGeo Userid which you
> can use to login to the site, and then hit "New Ticket" to file a bug
> report.  If you find this path isn't deducable from the main GDAL web
> page, please email me suggestions on how to improve things.
> Best regards,

Thanks a lot for your help, that gdalwarp string worked great.  I'll 
submit a ticket today as well!


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