[gdal-dev] Does the VRT SimpleSource element's OVERVIEW_LEVEL open option apply to the Overview element?
Sean Gillies
sean at mapbox.com
Mon Oct 8 14:03:42 PDT 2018
Dear group,
Does the OVERVIEW_LEVEL open option described in
https://www.gdal.org/gdal_vrttut.html#gdal_vrttut_format apply to VRT
Overview elements? It occurs to me that if it did, we could add external
overviews to a dataset using a single VRT file instead of the nested VRTs
shown in https://lists.osgeo.org/pipermail/gdal-dev/2012-July/033299.html.
For example, if I have a GeoTIFF with no overviews named cog_novr.tif and
another GeoTIFF at half resolution *with* overviews, I could virtually add
all those overview levels to the full resolution dataset like this (I
think?)
<VRTDataset rasterXSize="5080" rasterYSize="5194">
<SRS>...</SRS>
<GeoTransform>...</GeoTransform>
<VRTRasterBand dataType="UInt16" band="1">
<ColorInterp>Gray</ColorInterp>
<SimpleSource>
<SourceFilename relativeToVRT="1">cog_novr.tif</SourceFilename>
<SourceBand>1</SourceBand>
<SourceProperties RasterXSize="7621" RasterYSize="7791"
DataType="UInt16" BlockXSize="512" BlockYSize="512" />
<SrcRect xOff="0" yOff="0" xSize="7621" ySize="7791" />
<DstRect xOff="0" yOff="0" xSize="5080.22220278191"
ySize="5193.55553653945" />
</SimpleSource>
<Overview>
<!-- First overview is provided by the main image in the TIFF that
has all the overviews -->
<SourceFilename relativeToVRT="1">cog_ovrs.tif</SourceFilename>
<SourceBand>1</SourceBand>
<SourceProperties RasterXSize="3810" RasterYSize="3895"
DataType="UInt16" BlockXSize="512" BlockYSize="512" />
<SrcRect xOff="0" yOff="0" xSize="3810" ySize="3895" />
<DstRect xOff="0" yOff="0" xSize="5080.22220278191"
ySize="5193.55553653945" />
</Overview>
<Overview>
<!-- Second overview is provided by the first (index 0) overview of
the TIFF that
has all the overviews -->
<SourceFilename relativeToVRT="1">cog_ovrs.tif</SourceFilename>
<OpenOptions>
<OOI key="OVERVIEW_LEVEL">0</OOI>
</OpenOptions>
<SourceBand>1</SourceBand>
<SourceProperties RasterXSize="1905" RasterYSize="1948"
DataType="UInt16" BlockXSize="512" BlockYSize="512" />
<SrcRect xOff="0" yOff="0" xSize="1905" ySize="1948" />
<DstRect xOff="0" yOff="0" xSize="5080.22220278191"
ySize="5193.55553653945" />
</Overview>
</VRTRasterBand>
</VRTDataset>
With GDAL 2.2.4, gdalinfo tells me that this VRT has two overviews, but the
overview levels reported look suspicious:
Band 1 Block=128x128 Type=UInt16, ColorInterp=Gray
Overviews: 3810x3895, 3810x3895
I expected to see a 1905x1948 overview above.
Should I expect the open option to work? If not, could it be made to work
or does that go against the grain of VRT features?
--
Sean Gillies
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