On Thu, Sep 25, 2014 at 8:10 AM, Kyle Shannon <[email protected]> wrote: > Stephen, > > On Wed, Sep 24, 2014 at 2:21 PM, Stephen Roecker > <[email protected]> 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 >> [email protected] >> 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
Apologies, it does appear to be different, my mistake. -- Kyle _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
