[Qgis-user] Regression 2.18 to 3.4.1 in "Zoom to layer" and streaming raster using VRT

[Guy Doulberg]

Hi

I am a raster provider I am providing very big rasters in streaming using a
VRT file on top of many remotely GeoTiff.

Meaning I am providing a remote vrt file that is pointing to Geotifs that
can be accessed using /vsicurl/

I have created overviews as a cache layer on top of the vrt file, that can
also be accessed remotely

When opening the vrt on qgis 2.18.25 it reads only the vrt file and the ovr
file on full extent,
but when opening the vrt on the qgis 3.4.1 it reads the vrt file the
overviews and all of the geotiffs.

I debugged for a while, it seems that on 3.4.1 qgis read the overviews of
each of the geotiff when calling "Zoom to Layer"
I think that when I open the vrt file, qgis execute "Zoom to layer" and
fetches all the overviews.
After the initial opening, it seems that qgis continues as expected and
reads data only from the ovr file

When using gdalinfo on the vrt file gdal doesn't read each of geotiffs in
the VRT,  so what-else is executed when doing "zoom to layer"

I think that it is related to "Zoom to layer" because when I am in high
zoom level and go to "zoom to layer" I see in the GDAL debug it scans each
of the tiffs overviews

This thing is really important when providing a virtual raster on remote
location because it make the time it takes to see the raster on the map
much longer


I hope my case is clear cause it consist of many details

Thanks, Guy
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