Thank you, Jukka, for reproducing the behavior and explaining the reason behind it!
On Mon, Jun 10, 2024 at 9:19 AM Rahkonen Jukka < jukka.rahko...@maanmittauslaitos.fi> wrote: > Hi, > > > > Those two commands behave in quite different ways. With “-oo > OVERVIEW_LEVEL=1” the output size is the size of the second overview. In my > test case the original has 12000 x 12000 pixels and the command creates a > 3000 x 3000 sized output > > > > GDAL: GDALOverviewDataset(vrttest.vrt, this=000001CB3D728890) creation. > > GDAL: Using GTiff driver > > GDAL: Computing area of interest: 26.8805, 63.2011, 27, 63.255 > > Creating output file that is 3000P x 3000L. > > … > > GDAL: GDALWarpKernel()::GWKNearestNoMasksOrDstDensityOnlyByte() > Src=0,0,3000x3000 Dst=0,0,3000x3000 > > ...10...20...30...40...50...60...70...80...90...100 - done. > > > > With -ovr 1 the output has the size of the full resolution image, 12000 x > 12000 pixels, even the data is read from the 3000 x 3000 overview. The > pixels will be upsampled. > > > > GDAL: Using GTiff driver > > GDAL: Computing area of interest: 26.8805, 63.2011, 27, 63.255 > > Creating output file that is 12000P x 12000L. > > WARP: Selecting overview level 1 for vrttest.vrt > > … > > GDAL: GDALWarpKernel()::GWKNearestNoMasksOrDstDensityOnlyByte() > Src=0,0,1500x750 Dst=0,0,6000x3000 > > ...10.GDAL: GDALWarpKernel()::GWKNearestNoMasksOrDstDensityOnlyByte() > Src=1500,0,1500x750 Dst=6000,0,6000x3000 > > ..20..GDAL: GDALWarpKernel()::GWKNearestNoMasksOrDstDensityOnlyByte() > Src=0,750,1500x750 Dst=0,3000,6000x3000 > > .30...GDAL: GDALWarpKernel()::GWKNearestNoMasksOrDstDensityOnlyByte() > Src=1500,750,1500x750 Dst=6000,3000,6000x3000 > > 40...50GDAL: GDALWarpKernel()::GWKNearestNoMasksOrDstDensityOnlyByte() > Src=0,1500,1500x750 Dst=0,6000,6000x3000 > > ...60.GDAL: GDALWarpKernel()::GWKNearestNoMasksOrDstDensityOnlyByte() > Src=1500,1500,1500x750 Dst=6000,6000,6000x3000 > > ..70..GDAL: GDALWarpKernel()::GWKNearestNoMasksOrDstDensityOnlyByte() > Src=0,2250,1500x750 Dst=0,9000,6000x3000 > > .80...GDAL: GDALWarpKernel()::GWKNearestNoMasksOrDstDensityOnlyByte() > Src=1500,2250,1500x750 Dst=6000,9000,6000x3000 > > 90...100 - done. > > GDAL: Flushing dirty blocks: > 0...10...20...30...40...50...60...70...80...90...100 - done. > > > > The behavior is the same when using a TIFF with internal overviews as > input instead of VRT. Obviously the -ovr option has been designed to force > the use of some better-quality overview as source data when warping yields > a smaller, downsampled image. The forced upsampling does not make much > sense to me. I wonder if gdalwarp should even allow that? > > > > The gdal_translate utility has also -ovr option > https://gdal.org/programs/gdal_translate.html#cmdoption-gdal_translate-ovr. > It behaves in a different way when it comes to the size of the output, but > with gdal_translate it makes sense. > > “When -ovr is specified to an integer value, and none of -outsize and -tr > is specified, the size of the overview will be used as the output size.” > > > > Maybe the thing to do is to improve the documentation of the gdalwarp > option https://gdal.org/programs/gdalwarp.html#cmdoption-gdalwarp-ovr and > mention that this option does not have on effect on the size of the output. > > > > -Jukka Rahkonen- > > > > > > > > > > *Lähettäjä:* gdal-dev <gdal-dev-boun...@lists.osgeo.org> *Puolesta *Denis > Rykov via gdal-dev > *Lähetetty:* maanantai 10. kesäkuuta 2024 2.27 > *Vastaanottaja:* gdal dev <gdal-dev@lists.osgeo.org> > *Aihe:* [gdal-dev] Discrepancy in utilizing overviews with gdalwarp > > > > I'd anticipate that both commands would yield the same outcome: > > $ gdalwarp -oo OVERVIEW_LEVEL=1 -dstalpha input.vrt ovr1.tif > $ gdalwarp -ovr 1 -dstalpha input.vrt ovr1.tif > > > > However, the reality is different. The first command behaves as intended, > utilizing overviews from *.vrt.ovr, while the second command operates > noticeably slower, seemingly disregarding the overviews. >
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