[gdal-dev] gdalwarp performance with many GCPs

[Jan Hartmann]

On 12/12/2012 01:54 PM, Knut-Frode Dagestad wrote:
> The GCPs are completely regular, every 40 pixel in each direction. 
> Warping quality is very good (only slow), so the GCPs are probably 
> also ok.
>
> I would appreciate very much if you could download this file and test 
> the command below:
> http://dl.dropbox.com/u/15885758/testgcp.tif
>
> time gdalwarp -tps -t_srs '+proj=merc' testgcp.tif out.tif
>
> If it works fast for you, the problem should be related to my local 
> GDAL build (1.10).
>
It's far too slow here too, so it's not your build.

I see that the warp itself doesn't start but after a very long time, so 
the problem lies in the initial computation of the transformation 
matrix. It must have something to do with the distribution of points, 
perhaps too close together, so as to cause singularities. The target 
coordinates are latlon-values, very close numerically. I see two testing 
possibilities:

1) Try to warp with subsets of points
2) Multiply all target coordinates with (e.g.) 1000. You'll get an 
impossible georeference, but if this goes much faster, you know where 
the problem lies.

Jan
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/gdal-dev/attachments/20121212/65c872bf/attachment-0001.html>