[gdal-dev] overview sizes for COG
Hi, can we specify overview sizes exactly? I have this odd grid that is
36000x17999, and I get consequently yucky overview sizes:
gdal_create -outsize 36000 17999 -ot Int8 -co SPARSE_OK=YES -a_srs
EPSG:4326 -a_ullr 0 17999 0 36000 weird.tif
gdal_translate weird.tif cog.tif -of COG
gdalinfo cog.tif | grep Overviews
# Overviews: 18000x8999, 9000x4499, 4500x2249, 2250x1124, 1125x562,
562x281, 281x14
Should I worry about this? Can the sizes be specified via Translate? (I
can see how they could be generated externally and bundled, but I'm looking
for a way at this high level).
( Maybe I shouldn't even care about the sizes ... and maybe I should
resample the grid to be a better overall size, but I consider that out of
scope here.)
I'm comparing with other COG creators, e.g. odc which makes tidy overviews
( I will explore how it's getting done).
import xarray
from odc.geo.xr import assign_crs
from odc.geo.cog import write_cog
ds = xarray.open_dataset("weird.tif")
ds = assign_crs(ds, crs="EPSG:4326") ## do something to tag it as odc
write_cog(ds["band_data"], "odc.tif")
os.system("gdalinfo odc.tif | grep Overviews")
# Overviews: 18000x9000, 9000x4500, 4500x2250, 2250x1125, 1125x563
Cheers, Mike
--
Michael Sumner
Software and Database Engineer
Australian Antarctic Division
Hobart, Australia
e-mail: mdsum...@gmail.com
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Re: [gdal-dev] overview sizes for COG
Michael, Hi, can we specify overview sizes exactly? No, the BuildOverviews() interface onlys take an array of overview factors. It is up to the driver implementation to decide how it computes the overview size from the main raster size and overview factor. The COG driver is a bit of a special case, since it automagically compute overviews if they don't exist in the source dataset, and doesn't take an explicit list of overview factors. It simply divides by two successively, with floor truncation: https://github.com/OSGeo/gdal/blob/master/frmts/gtiff/cogdriver.cpp#L1092 I have this odd grid that is 36000x17999, and I get consequently yucky overview sizes: gdal_create -outsize 36000 17999 -ot Int8 -co SPARSE_OK=YES -a_srs EPSG:4326 -a_ullr 0 17999 0 36000 weird.tif gdal_translate weird.tif cog.tif -of COG gdalinfo cog.tif | grep Overviews # Overviews: 18000x8999, 9000x4499, 4500x2249, 2250x1124, 1125x562, 562x281, 281x14 Should I worry about this? Probably not ? :-) Can the sizes be specified via Translate? (I can see how they could be generated externally and bundled, but I'm looking for a way at this high level). I guess someone could potentially add a OVERVIEW_SIZES=W1xH1,W2xH2,... creation option to the COG driver if that was really needed... ( Maybe I shouldn't even care about the sizes ... and maybe I should resample the grid to be a better overall size, but I consider that out of scope here.) I'm comparing with other COG creators, e.g. odc which makes tidy overviews ( I will explore how it's getting done). It looks like they might use (previous_size + 1) / 2 (or ceil rounding) -- http://www.spatialys.com My software is free, but my time generally not. ___ gdal-dev mailing list gdal-dev@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/gdal-dev
Re: [gdal-dev] overview sizes for COG
Excellent! Thanks for the answers. When I've explored a bit more I might implement the overview sizes just so we can match downstream tools (the current motivation is like-for-like performance comparison, I haven't looked there but I think odc goes very low level to eke out speed). Cheers, Mike On Wed, Mar 20, 2024 at 10:39 AM Even Rouault wrote: > Michael, > > Hi, can we specify overview sizes exactly? > > No, the BuildOverviews() interface onlys take an array of overview > factors. It is up to the driver implementation to decide how it computes > the overview size from the main raster size and overview factor. > > The COG driver is a bit of a special case, since it automagically compute > overviews if they don't exist in the source dataset, and doesn't take an > explicit list of overview factors. It simply divides by two successively, > with floor truncation: > https://github.com/OSGeo/gdal/blob/master/frmts/gtiff/cogdriver.cpp#L1092 > > I have this odd grid that is 36000x17999, and I get consequently yucky > overview sizes: > > gdal_create -outsize 36000 17999 -ot Int8 -co SPARSE_OK=YES -a_srs > EPSG:4326 -a_ullr 0 17999 0 36000 weird.tif > gdal_translate weird.tif cog.tif -of COG > gdalinfo cog.tif | grep Overviews > # Overviews: 18000x8999, 9000x4499, 4500x2249, 2250x1124, 1125x562, > 562x281, 281x14 > > Should I worry about this? > > Probably not ? :-) > > Can the sizes be specified via Translate? (I can see how they could be > generated externally and bundled, but I'm looking for a way at this high > level). > > I guess someone could potentially add a OVERVIEW_SIZES=W1xH1,W2xH2,... > creation option to the COG driver if that was really needed... > > > ( Maybe I shouldn't even care about the sizes ... and maybe I should > resample the grid to be a better overall size, but I consider that out of > scope here.) > > I'm comparing with other COG creators, e.g. odc which makes tidy overviews > ( I will explore how it's getting done). > > It looks like they might use (previous_size + 1) / 2 (or ceil rounding) > > -- http://www.spatialys.com > My software is free, but my time generally not. > > -- Michael Sumner Software and Database Engineer Australian Antarctic Division Hobart, Australia e-mail: mdsum...@gmail.com ___ gdal-dev mailing list gdal-dev@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/gdal-dev
