Fix to prevent negative size values in gdal2tiles.py

[antonmyagotin]

Problem:
Gdal2tiles crashes with the message "Illegal values for buffer size". The problem was reported in multiple source and exists already for years. Examples:
https://gis.stackexchange.com/questions/249809/gdal2tiles-error-5-illegal-values-for-buffer-size-error-for-a-single-zoom-lev

Solution:
We just skip the tile with negative extent values.

[rouault]

@antonmyagotin https://gis.stackexchange.com/questions/249809/gdal2tiles-error-5-illegal-values-for-buffer-size-error-for-a-single-zoom-lev is about size = 0. Do you have a reproducer with negative sizes ?

[antonmyagotin]

yes, for several big geotiffs I can reproduce the crash

[rouault]

yes, for several big geotiffs I can reproduce the crash

Please use "gdal_create" with options "-co TILED=YES -co SPARSE_OK=YES" to create an empty file with the same characteristics, and attach it there (zipped), and also the exact gdal2tiles command line you use

[antonmyagotin]

Sorry for the delay, it took some time to generate smallest reproducable example

small_sample.zip
I use following sequence of command

create original vrt file

gdalbuildvrt -input_file_list filelist.txt original.vrt

create scaled vrt

gdal_translate -of VRT -ot Byte -a_nodata 0 -scale -15 15 1 255 original.vrt scaled.vrt

and finally generate tiles

gdal2tiles --processes 8 --tilesize=256 --tiledrive=PNG  scaled.vrt

it gives an error:
The above exception was the direct cause of the following exception:

Traceback (most recent call last):
File "/usr/bin/gdal2tiles", line 33, in
sys.exit(load_entry_point('GDAL==3.9.3', 'console_scripts', 'gdal2tiles')())
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/osgeo_utils/gdal2tiles.py", line 4693, in main
return submain(argv, called_from_main=called_from_main)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/osgeo_utils/auxiliary/util.py", line 62, in enable_exceptions_wrapper
return fun(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/osgeo_utils/gdal2tiles.py", line 4723, in submain
multi_threaded_tiling(input_file, output_folder, options, pool)
File "/usr/lib/python3/dist-packages/osgeo_utils/auxiliary/util.py", line 62, in enable_exceptions_wrapper
return fun(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/osgeo_utils/gdal2tiles.py", line 4617, in multi_threaded_tiling
for _ in pool.imap_unordered(
File "/usr/lib/python3.12/multiprocessing/pool.py", line 451, in
return (item for chunk in result for item in chunk)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.12/multiprocessing/pool.py", line 873, in next
raise value
RuntimeError: Illegal values for buffer size

Checking out actual values for rxsize, rysize, wxsize, wysize I see that they are negative.

[jratike80]

It seems to work well with the new alternative https://gdal.org/en/stable/programs/gdal_raster_tile.html
Perhaps there is no need to touch the old python utility any more.

gdal raster tile scaled.vrt output
0...10...20...30...40...50...60...70...80...90...100 - done.

[rouault]

closing this PR as it only fixes the symptom and not the root cause. Proper fix in #14115