On Wed, Jun 13, 2018 at 11:03 PM, Even Rouault <even.roua...@spatialys.com> wrote: > > On mercredi 13 juin 2018 22:14:07 CEST Markus Metz wrote: > > Many raster bands contain nodata, therefore it would be helpful if the > > number of non-nodata grid cells could be reported by gdalinfo in some way. > > > > The number of non-nodata grid cells is not available through > > GDALGetRasterStatistics() / GDALRasterBand::GetStatistics(), probably > > because approximations can be stored as raster band statistics, and the > > number of non-nodata grid cells is unknown in case of approximations. > > > > Therefore I suggest to report the number of non-nodata grid cells only if > > all grid cells are evaluated, i.e. with > > > > *gdalinfo -mm* Force computation of the actual min/max values for each band > > in the dataset. > > > > The number of non-nodata grid cells would be a small piece of quite useful > > information to quickly evaluate the usefulness of a raster band. > > > > Asking for the possibility to enhance a bit the output of gdalinfo, > > Markus, > > That would be more something triggered by -stats since this number of non- > nondata cells is an intermediate result of GDALRasterBand::ComputeStatistics() > in gcore/gdalrasterband.cpp. To make it sensical even in the case of > approximate statistics, why not computing a percentage instead ? That would > need to be saved in a metadata item, let's say STATISTICS_VALID_RATIO (between > 0 and 1) ?
Considering approximate statistics, something like STATISTICS_VALID_RATIO would make sense. However, I am not interested in approximate statistics, therefore my suggestion to tie it to -mm. > Wanna take a crack at implementing this ? Too many API changes required, starting with GDALGetRasterStatistics(), GDALComputeRasterStatistics() and all else following. There must be an easier solution. But thanks for your offer:-) My workaround is to use GRASS r.external to get correct raster band statistics. > Otherwise file an > enhancement ticket about that. > By the way, since GDAL 2.3.0, there's a STATISTICS_APPROXIMATE=YES metadata > item so as to know if the stats have been computed in an approx way or not Enhancement request: set STATISTICS_APPROXIMATE=UNKNOWN if it is unknown. I checked with some externally provided sample data and GDAL 2.3.0 does not report STATISTICS_APPROXIMATE. I understand that GDAL has to cater for approximate statistics and should not override metadata provided with raster bands created by other software. It would help if STATISTICS_APPROXIMATE is always set to NO|YES|UNKNOWN. Markus
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