[gdal-dev] Reading a VRT file & overview usage

[Even Rouault]

Angus,

The difference of behaviour between my test case and yours is that yours has a 
<NoDataValue> set on the VRTRasterBand, and the source COGs don't have that 
value. In this situation a key optimization used by the VRT driver is 
disabled, and there's a fallback to code that won't make use of the source 
overviews to get correct results. I imagine that could be improved, but this 
is not a 5-minute type of fix. A workaround would probably to create your COGs 
with 0 set as nodata value.

Even


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