On 12. des. 2012 14:16, Jan Hartmann wrote:
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
Scaling lon and lat with 1000 did not help, but when using only every
5th GCP in each direction it is very fast (3 seconds with -tps) and
still with good accuracy (as long as I keep the border GCPs).
So thank you, Jan, for spotting the problem!
It might be useful with a -decrease-GCP-density-factor switch which the
user could fine-tune for performance, or ideally that the warping
routines would calculate the optimal factor directly.
Another thing: I originally wanted to warp using Python API
(AutoCreateWarpedVRT), but it seems to have no option to use -tps (?) -
so therefore I have to call gdalwarp as system command.
Knut-Frode
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