On mardi 28 janvier 2020 11:49:01 CET Daniel Evans wrote: > Hi all, > > I've recently tried enabling the GDAL_FORCE_CACHING option, and found it > gives some significant improvements to TIFF/VRT read speeds. > > However, using GDAL 2.3.0, I've now found that when reading large VRTs, I > can sometimes get subtly different values - up to about 1% summed > difference across a 1000x1000 or so area. Is there a known issue in > GDAL_FORCE_CACHING in this older version of GDAL, or alternatively have I > misunderstood the use of this option and is this expected behaviour?
GDAL_FORCE_CACHING will force I/O requests to happen exactly on VRT block boundaries. So what you observe is slight inconsistencies in results depending on the window passed to the VRT driver. I see that 2.4.0 had a potentially related fix """VRT: fix source window computation that caused sub-pixel shift with non- nearest resampling""" But if you use a warped VRT, then what you observe is somewhat expected. gdalwarp due to approximations in some computations doesn't lead to "consistent" results if you change the output window. See https://lists.osgeo.org/pipermail/gdal-dev/2019-November/051177.html Even -- Spatialys - Geospatial professional services http://www.spatialys.com _______________________________________________ gdal-dev mailing list [email protected] https://lists.osgeo.org/mailman/listinfo/gdal-dev
