[gdal-dev] gdalwarp performance with many GCPs

[Jan Hartmann]

Hi Knut,

What do you mean by "very slow"? I regularly use gdalwarp -tps on much 
larger rasters with a few thousand gcp-s, and never noticed unacceptable 
delays. Do you have very little physical memory, or many parallel 
processes running?

Jan

On 12/12/2012 01:12 PM, Knut-Frode Dagestad wrote:
> Hi list,
>
> When warping images with many GCPs, the -tps switch (Thin Plate 
> Spline) is found to be necessary to get decent accuracy. This makes 
> however warping very slow. The only method I found to increase speed 
> is the -et switch, but at cost of spatial accuracy.
>
>
> Below some comments about the other tries which did not help:
>
> - compiling GDAL with armadillo support had no effect on speed.
> Btw, to compile with armadillo I had to manually insert -llapack in 
> the following line in configure:
> if test -z "`${CXX} testarmadillo.cpp -o testarmadillo -larmadillo 
> 2>&1`" ; then .....
> Perhaps ${LIBS} should be added permanently to this line in trunk?
>
> - compiling GDAL with OpenCL had also no effect. At first surprising, 
> but looking at the opencl warp kernel it seems that it only makes a 
> difference for other resampling algorithms than nearest neighbour?
>
> - Increasing  memory with -wm had no effect
>
> - Using several threads (-multi -wo NUM_THREADS=ALL_CPUS) actually 
> increased computing time significantly (my proj version is 4.7.1).
>
> From the debug output, a lot of the time is apparently spent on:
> "WARP: Copying metadata from first source to destination dataset"
> Is this an indication that much time is simply spent on reading and 
> writing the GCPs to/from file? If so, we could perhaps expect improved 
> performance if Geolocation Arrays could be used instead (not possible 
> due to http://trac.osgeo.org/gdal/ticket/4907).
>
>
> The tests are made with the following file and command on Ubuntu:
> http://dl.dropbox.com/u/15885758/testgcp.tif  (3212 GCPs and 2048x2511 
> pixels covering Southern Europe)
>
> time gdalwarp --debug on -et 5 -tps -t_srs '+proj=merc' testgcp.tif 
> out.tif  (+ other swithces mentioned above)
>
>
> Best regards from Knut-Frode
>
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/gdal-dev

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/gdal-dev/attachments/20121212/9617a560/attachment.html>