[gdal-dev] Strange things with gdalwarp ...

[Felix Schalck]

Hello,

As explained in my previous question, I'm trying to create a high
resolution topographic map of europe based on cgiar processed srtm
data. Of cours, the first step is to merge the 5*5° tif tiles into one
big tif, which can be achieved using gdalwarp's mosaic feature.

Simply pasting all the tiles togther trough following code:

gdalwarp --config GDAL_CACHEMAX 512 -wm 512  HDA1/srtm_*.ti HDA2/final.tif

takes about 20 hours. HDA1/2 are two different harddrives.

Now, a second script, pasting first "slices" of 5*30° together, and
than merging all the slices:

for i in 39 40 41 42 43; do
gdalwarp --config GDAL_CACHEMAX 512 -wm 512 HDA1/srtm_$i*.tif
HDA2/slice_0$((i-34)).tif
done
gdalwarp --config GDAL_CACHEMAX 512 -wm 512 HDA2/slice_*.tif HDA1/final.tif

takes less than on hour ! Filesize is similar.

So what is the trick here ? Is there some quality loss when using gdalwarp ?

Felix Schalck