[gdal-dev] gdalwarp cutting off projected image

[Even Rouault]

Le Tuesday 09 December 2008 18:51:59 Scott Lewis, vous avez écrit :
> Frank,
>
> Thanks for the help.  I tried doing this, and ended up with the same
> image (even diff found them to be the same).  Here are the various
> commands I tried.  Maybe I'm just using the -wo option wrong.
>
> gdalwarp -t_srs EPSG:4326 -wo SOURCE_EXTRA=1000 input.gtiff.tif
> output1.gtiff.tif
> gdalwarp -t_srs EPSG:4326 -wo "SOURCE_EXTRA=1000" input.gtiff.tif
> output2.gtiff.tif

> gdalwarp -t_srs EPSG:4326 -wo "SOURCE_EXTRA=1000 SAMPLE_GRID=YES
> SAMPLE_STEP=100" input.gtiff.tif output3.gtiff.tif

This last one won't work as you expect. You should repeat -wo in front of each 
option :
gdalwarp -t_srs EPSG:4326 -wo SOURCE_EXTRA=1000 -wo SAMPLE_GRID=YES -wo 
SAMPLE_STEP=100 input.gtiff.tif output3.gtiff.tif

>
> I'll continue to play with those options, though.  gdalwarp seems to not
> act any different (IE, it takes the same amount of time to process) with
> or without the -wo option, so I'm thinking I'm just not using the option
> correctly somehow.
>
> Again, I appreciate your help!
>
> Scott
>
> Frank Warmerdam wrote:
> > Scott Lewis wrote:
> >> Hi,
> >>
> >> I'm fairly new with GDAL, and have been working with a coworker who
> >> is a little more familiar with GDAL and gdalwarp, but we are both
> >> stumped by this particular issue.
> >>
> >> I have a GeoTiff image that is in a north polar Lamber Azimuthal
> >> Equal Area (laea) projection.  I am trying to reproject it using
> >> gdalwarp to a cylindrical projection (like EPSG:4326).  I am using
> >> the following command:
> >>
> >> gdalwarp -t_srs EPSG:4326 input.gtiff.tif output.gtiff.tif
> >>
> >> The tool runs OK, but when I open output.gtiff.tif, the projection is
> >> "incomplete".  The parts that are there look correct, but it seems
> >> everything above about 50 degrees is cut off, like the
> >> input.gtiff.tif had a big circle around 50 degrees cut out before the
> >> reprojection was made.
> >>
> >> I've tried looking at the options for gdalwarp, but can't seem to
> >> find anything that would help.
> >
> > Scott,
> >
> > There are various challenges in pole (or even dateline) spanning
> > reprojection operations.  The options at:
> >
> > http://www.gdal.org/structGDALWarpOptions.html#0ed77f9917bb96c7a9aabd73d4
> >d06e08
> >
> >
> > may be helpful.
> >
> > In particular, you might try specifying -wo SOURCE_EXTRA=1000 or some
> > similar
> > large value on the gdalwarp commandline.  It is also possible that the
> > SAMPLE_GRID=YES and SAMPLE_STEPS=100 options might help but generally if
> > you have lots of RAM and a not-too-big input image specifying a large
> > SOURCE_EXTRA value will resolve the issues.
> >
> > Best regards,
>
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