Le Wednesday 06 May 2009 16:48:06 Andreas Neumann, vous avez écrit : > Hi, > Filename: a25.tif > File Size: 25472x25427x1 > Pixel Size: 42.431795 x -42.431795 > UL:(697837651.400476,244274906.596461) > LR:(698918474.082743,243195993.344970) > Copy 0,0,25472,25427 to 205747,211643,50722,50632.
--> here's the issue. a25.tif is resampled from 25472x25427 to a 50722x50632 raster. But as gdal_merge.py just operates on full buffers, this results in trying to allocate 50722x50632 pixels = 2 568 156 304 bytes, which is above the largest 32 bit (signed) integer whose value is 2 147 483 647. So this value is interpreated as a negative size by Python... To make the story short, you didn't do anything wrong. You've just hit a known limitation of gdal_merge.py. The issue is that the default pixel size used for the destination merged file is the pixel size of the first source raster processed, in your case 21.309260 x -21.309260 for a01.tif. But a25.tif on which the error occurs has a pixel size of 42.431795 x -42.431795. So it must be nearly over-sampled by a factor of 2, so that accounts for his size going from 25472x25427 to a 50722x50632. There are several workarounds : - use the -ps flag of gdal_merge.py to increase the pixel size of the destination raster. "-ps 30 30" would probably work (provided that you've enough memory) - or add a preprocessing step that cuts a25.tif into 4 smaller pieces. This can be done with 4 calls to gdal_translate by using the -srcwin option - or use gdalwarp to do the same thing. It has not the limitation of gdal_merge.py, but it is known to be much slower. Patches to improve gdal_merge.py are welcome ;-) > Traceback (most recent call last): > File "/usr/local/bin/gdal_merge.py", line 427, in <module> > fi.copy_into( t_fh, band, band, nodata ) > File "/usr/local/bin/gdal_merge.py", line 227, in copy_into > nodata_arg ) > File "/usr/local/bin/gdal_merge.py", line 47, in raster_copy > nodata ) > File "/usr/local/bin/gdal_merge.py", line 83, in raster_copy_with_nodata > t_xsize, t_ysize ) > File > "/usr/lib/python2.5/site-packages/GDAL-1.6.0-py2.5-linux-x86_64.egg/osgeo/g >dal.py", line 835, in ReadAsArray > buf_xsize, buf_ysize, buf_obj ) > File > "/usr/lib/python2.5/site-packages/GDAL-1.6.0-py2.5-linux-x86_64.egg/osgeo/g >dal_array.py", line 133, in BandReadAsArray > buf_xsize, buf_ysize, datatype ) > File > "/usr/lib/python2.5/site-packages/GDAL-1.6.0-py2.5-linux-x86_64.egg/osgeo/g >dal.py", line 760, in ReadRaster > return _gdal.Band_ReadRaster(*args, **kwargs) > SystemError: Negative size passed to PyString_FromStringAndSize > ------------------- > > Is this a problem with my data, georeferencing or projection or is it a > problem in gdal_merge? > > Thanks for any idea what might be wrong in this case! > > Andreas _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
