[gdal-dev] gdalwarp performance with many GCPs

[Knut-Frode Dagestad]

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).


On 12. des. 2012 13:40, Jan Hartmann wrote:
> No, this is unaaceptable, but I cannot reproduce it. The only problem I
> had was with control points that were too close together. Are yours
> evenly distributed? Can you do tests with subsets of control points?
>
> On 12/12/2012 01:27 PM, Knut-Frode Dagestad wrote:
>> Hi Jan,
>>
>> That sounds interesting and promising.
>>
>> For the mentioned file it takes about 2 minutes with "-et 5" (low
>> accuracy), and 12 minutes without this switch. Without -tps it takes
>> less than 0.5 seconds.
>> The machine is quite decent with 16 GB memory and SSD disk.
>>
>> Best regards from Knut-Frode
>>
>>
>>
>> On 12. des. 2012 13:24, Jan Hartmann wrote:
>>> 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
>>>>
>>>> _______________________________________________
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>>>
>>>
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