Hi Paolo,
the te option set the output raster size, not the subraster. You have to
use gdal_translate to get subraster and then use gdalwarp.
Also *multi option is preferable to multi threaded execution.
*
Best regards,
Dmitry
24.12.2013 21:48, Paolo Corti ?????:
Hi all
I am experiencing problems using a VRT dataset built from a large
directory of .tif files.
While if a build the VRT from just one of these datasets, gdalwarp
will work very fast with it, if I use the VRT will all of these
images, it becomes undefinite times slower.
Debugging the gdalwarp command, it seems that gdalwarp accesses every
single raster composing the vrt datasource, even if that single raster
is not within the extent defined by the -te gdalwarp option.
Here is the output for a vrt composed by just one single .tif file:
$ time gdalwarp -te -88.88 20.28 -87.88 21.28 single.vrt single.tiff
...
Src=1344,4463,1201x1201 Dst=0,0,1200x1200
0...10...20...30...40...50...60...70...80...90...100 - done.
GDAL: GDALClose(single.vrt, this=0x8ca6ef8)
GDAL: GDALClose(/home/capooti/training/vrt/srtm_19_08.tif, this=0x8ca9aa8)
GDAL: GDALClose(/home/capooti/training/vrt/srtm_19_08.tif, this=0x8ca7208)
GDAL: GDALClose(single.tiff, this=0x8ca7e98)
GDAL: In GDALDestroy - unloading GDAL shared library.
real 0m0.137s
user 0m0.076s
sys 0m0.052s
and here is the output for a vrt composed of all of the .tif files:
capooti@ubuntu:~/training/vrt$ time gdalwarp -te -88.88 20.28 -87.88
21.28 all.vrt all.tiff
...
Src=7344,16464,1201x1201 Dst=0,0,1200x1200
0...10...20...30...40...50...60...70...80...90...100 - done.
GDAL: GDALClose(all.vrt, this=0x9d332b0)
GDAL: GDALClose(/home/capooti/training/vrt/srtm_18_09.tif, this=0x9d46618)
GDAL: GDALClose(/home/capooti/training/vrt/srtm_19_08.tif, this=0x9d467c8)
...
GDAL: GDALClose(/home/capooti/training/vrt/srtm_35_09.tif, this=0x9d4c1b8)
GDAL: GDALClose(/home/capooti/training/vrt/srtm_35_10.tif, this=0x9d4c3a8)
GDAL: GDALClose(/home/capooti/training/vrt/srtm_19_08.tif, this=0x9d30800)
GDAL: GDALClose(/home/capooti/training/vrt/srtm_35_11.tif, this=0x9d4c630)
GDAL: GDALClose(all.tiff, this=0x9d33990)
GDAL: In GDALDestroy - unloading GDAL shared library.
real 61m12.130s
user 0m6.076s
sys 0m18.052s
Any hint here to prevent gdalwarp to access the unneeded source raster
files - the defined extent in -te should just hit a couple of ones?
thanks in advance
p
--
Paolo Corti
Geospatial software developer
web: http://www.paolocorti.net
twitter: @capooti
skype: capooti
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