[gdal-dev] reprojection of global rasters to mollweide

[Michael Schulz]

Dear Even,

thanks for your response, finally I got it working. The main issue was that
the global dataset had an extent e.g. on the most western border of
-180.0044643 which caused the error (although strangely not always, because
I tried the same command with the same dataset and sometime it worked...)

Anyhow, clipping the data before and then specifying as you suggested the
target extent (-te) works now.

Cheers, Michael


2012/8/1 Even Rouault <even.rouault at mines-paris.org>

> Le mardi 31 juillet 2012 11:32:35, Michael Schulz a écrit :
> > Dear GDAL'ers,
> >
> > I have currently some issues with reprojecting global datasets in
> > geographic coordinates to the Mollweide projection (GDAL 1.8.0). When
> using
> > gdalwarp like:
> >
> > gdalwarp -s_srs 'EPSG:4326' -t_srs '+proj=moll +lon_0=0 +x_0=0 +y_0=0
> > +ellps=WGS84 +datum=WGS84 +units=m +no_defs' LatLon.2001.tree.nd.tif
> > Mollweide.2001.tree.nd.tif
> >
> > unpredictably, it sometimes works but other times I get the "Too many
> > points (441 out of 441) failed to transform" error. I was wondering
> whether
> > this could be a memory size issues (although the machine I'm working has
> > 24GB RAM).
>
> No, memory isn't the reason. The reason is that the algorithm used by
> gdalwarp
> doesn't manage to guess the extent of the raster once reprojected. It may
> or
> may not succeed depending on the extent of the source image and the
> reprojection involved. If you know the extent in the target coordinate
> system,
> specifying it with -te will solve that issue.
>



>
> >
> > To overcome this adding the config option CHECK_WITH_INVERT_PROJ FALSE
> > works, but now the projected raster shows wrapped values outside the
> actual
> > valid coordinate range for Mollweide, e.g. the Aleutian Islands appear
> > twice (once inside the outer ellipse. Is this due to
> > the CHECK_WITH_INVERT_PROJ ?
>
> The default value of CHECK_WITH_INVERT_PROJ (YES) checks that when a
> reprojection of a coordinate is done, the invert reprojection gives a
> result
> close to the original coordinate, which validates the fact that we are in
> the
> validity area of the reprojection. If you override with
> CHECK_WITH_INVERT_PROJ=FALSE, you can have indeed strange artifacts due to
> non
> invertible transformations.
>
> > I haven't worked with the cutline option
> > before, but should/could this be used here to solve this?
>
> I don't think this will help.
>
> >
> > Happy about any feedback on this issue. Thanks, Michael
>



-- 
-----------------------------------------------------------
Michael Schulz

Via Cime Bianche 10
IT-21023 Besozzo (VA)
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