On vendredi 26 octobre 2018 09:09:34 CEST Vincent Sarago wrote: > Goal: I’d like to see if there could be a way to use VRT of COG to create a > mbtile like system to read tiles. > > If I remember well when a VRT points to COG you still need to create > external overviews for the whole VRT because it won’t fetch de overviews > from the COG itself when trying decimated read.
No, that's not exactly true. If a VRT contains more than one source, GDAL won't be able to expose a proper overview externaly, but it will use the overviews of sources, when present, for decimated read (*). However if your VRT has a lot of sources (let's 1024x1024 tiles of 256x256 pixel each), if you ask for just a 1024x1024 output buffer of the whole extent, there is no magic: GDAL will have to open each source dataset to compute its contributed single pixel. In that case, you may want to pregenerate an overview of the whole VRT. Even (*) and actually even if those don't expose overviews proper, it will let the underlying driver handle that at best: so a VRT of VRT of COG would work -- Spatialys - Geospatial professional services http://www.spatialys.com _______________________________________________ gdal-dev mailing list [email protected] https://lists.osgeo.org/mailman/listinfo/gdal-dev
