I've just implemented an improvement in gdalwarp to automatically set the 
existing SKIP_NOSOURCE=YES warping option when it is safe to do so. This 
option helps improving performance when a source dataset doesn't cover the 
full size of the output dataset. This is particularly interesting when warping 
into a fixed tiling scheme and/or when use gdalwarp in mosaicing situations. 
On a test scenario where the output tile is much larger than the extent of the 
source datasets, this for example cut down the time from 14 seconds to 2 

The logic to determine when SKIP_NOSOURCE=YES can be automatically set isn't 
trivial, so please test and report if there are situations where this would 
result in unexpected results.

Note that this will result in files potentially binary different than before 
(blocks not being written in the same order), but the pixel values as read by 
GDAL should be the same as without the optimization.


Spatialys - Geospatial professional services
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