[gdal-dev] Problem when creating overviews for large input files with gdaladdo

[Even Rouault]

Armin,

This is a "well known" performance issue with the geotiff driver / libtiff when switching back 
and forth between IFD (image file directories). At ~ 75%, you start generating overview 
factor 4 and that implies switching regularly between the one previously computed (read 
operations) and the new one (write operations). Each time you switch, you need to read and 
write the TileOffsets and TileByteCounts tags (those can be 10's of megabytes large on huge 
file, and are the root cause for the performance problem). With infinite patience, this would 
eventually complete.

A trick you can use is :

gdaladdo -ro --config COMPRESS_OVERVIEW LZW  INPUT_FILE 2
gdaladdo -ro --config COMPRESS_OVERVIEW LZW  INPUT_FILE.ovr 2
gdaladdo -ro --config COMPRESS_OVERVIEW LZW  INPUT_FILE.ovr.ovr 2
gdaladdo -ro --config COMPRESS_OVERVIEW LZW  INPUT_FILE.ovr.ovr.ovr 2

Even



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