Stephen, On Wed, Sep 24, 2014 at 2:21 PM, Stephen Roecker <stephen.roec...@gmail.com> wrote: > Out of curiousity the other day I compared the results of gdalwarp (-r > average) against the raster R package aggregate(fun=mean) function > for aggregating a raster to a coarser resolution. I was suprized how > different the results of gdalwarp were from raster. When zooming in > and manually averaging the overlapping cells, the results of gdal were > off. > > The elevation difference between the raster and gdal aggregated > rasters only averaged 0.66 meters, but had a max of 12 meters. Also > when subtracting the raster and gdal aggregated rasters, the resulting > subtracted layer looked like a hillshade, suggesting the GDAL > aggregated raster was shifted. However the raster and GDAL rasters > overlapped perfectly, so I can only assume the shift occured during > the aggregation process. > > Can someone explain gdal's behavior to me? Why the difference, is this > a bug in gdal? gdalwarp claims it's averaging all the overlapping > cells except the NA. That doesn't seem to be the case. FYI I'm using > GDAL 1.10.1 > > See a reproduceable R example below. > > Stephen > > library(gdalUtils) > library(raster) > > src_dataset <- system.file("external/tahoe_lidar_bareearth.tif", > package="gdalUtils") > test <- raster(x=src_dataset) > > writeRaster(test, "test.tif", overwrite=T) > gdal_setInstallation(search_path="C:/ProgramData/QGIS/QGISDufour/bin", > rescan=T, verbose=T) > gdalwarp(srcfile=src_dataset, dstfile="test_gdal.tif", of="GTiff", > r="average", ot="Float32", tr=res(test)*3, overwrite=TRUE, > verbose=TRUE) > > aggregate(x=raster(src_dataset), fact=3, filename="test_raster.tif", > format="GTiff", NAflag=-99999, > progress="text", overwrite=T) > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/gdal-dev
Without looking too far into it, it seems similar to: http://trac.osgeo.org/gdal/ticket/5311 -- Kyle _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev