Le 2012-09-13 16:28, Rutger a écrit :
Dear list,
Im using the gdalwarp command-line utility on Windows and im running
into
some strange behavior. When reprojecting a large global grid to a
subset,
the output filesize is way too large. Its a lot larger than
xsize*ysize*datatype, and when pulling the file through
gdal_translate
shrinks the filesize to normal proportions. This occurs only when i
run
gdalwarp with "COMPRESSION=PACKBITS", with no compression the results
from
gdalwarp seem fine.
The GDAL version im using is: GDAL 1.9.1, released 2012/05/16
I can reproduce the problem with the following example data:
The GMTED elevation dataset from the USGS, which can be found at:
http://topotools.cr.usgs.gov/GMTED_viewer/gmted2010_global_grids.php
The "Mean Statistic, 30 arc-seconds" is about 270MB. The effect is
much more
prominent with the 7.5 arc second file, which is about 3.1 GB! The
data is
delivered as an Arc/Info Binary Grid.
I have tested it with several projections and different regions, for
example
the United States, reprojecting with gdalwarp like this:
gdalwarp -ot Float32 -co "COMPRESS=PACKBITS" -r bilinear -t_srs
"+proj=lcc
+lat_1=20 +lat_2=60 +lat_0=40 +lon_0=-96 +x_0=0 +y_0=0 +ellps=GRS80
+datum=NAD83 +units=m +no_defs" -ts 10400 5800 -te -2600000 -1600000
2600000
1300000 hdr.adf GMTED.tif
After gdalwarp the output is 401 MB, for a float32, i would expect an
upper
limit of about 10400*5800*4 = 230MB. When running gdal_translate with
no
compression and no other settings whatsoever the file size reduces to
235MB,
which seems ok. With packbits compression it reduces further to
154MB.
So for the 30 arc second dataset, the initial gdalwarp result is
about 2.5
times to large. When using the higher resolution 7.5 arc second input
(but
otherwise the same procedure), the file sizes are:
after gdalwarp with packbits: 626MB
after gdal_translate: 235MB
after gdal_translate with packbits: 154MB
Making the gdalwarp result 4 times 'too large'. The effect seems
larger with
the higher resolution input data, even with exactly the same output
settings. I have also tried to first convert the Arc/Info binary grid
to a
Geotiff and then starting the entire procedure, this produces the
same
results.
Has anyone else ever noticed this behavior? And is there something i
can do
to prevent it?
Thanks in advance.
Regards,
Rutger
Add -wo OPTIMIZE_SIZE=TRUE
the process will be longer but the file will be similar to the output
of gdaltranslate
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