[gdal-dev] read a catalog is slower then directly the raster ?

Even Rouault even.rouault at mines-paris.org
Tue Jan 31 09:32:23 EST 2012

Selon Dmitry Baryshnikov <polimax at mail.ru>:

> 31.01.2012 16:54, Andrea Peri ?????:
> > Hi,
> > using qgis I notice that it is more slow to open some raster from a
> > catalog.vrt rather than opening the same raster directly.
> > The slow is so big that when the catalog has many raster qgis take
> > many time to open the catalog.
> >
> > Because qgis use gdal to read raster and also to read a catalog.
> > I guess this is not an issue for qgis. But is a question of gdal.
> >
> > Before to start to do some test I like to know if there is some know
> > issue on this.

> I think this bug are mentioned in such tickets
> http://trac.osgeo.org/gdal/ticket/2076 and
> http://trac.osgeo.org/gdal/ticket/3482
> QGIS more slow because it warp image (if it from VRT or have some
> rotation in meta and etc.) and have no overviews. You can see if image
> is warped in layer properties metadata tab -> driver.

Yes that's one possibility. A more pragmatic way would be to run qgis under
GDB/DDD, and when it is stuck, Ctrl+C to see in which GDAL function it is
stuck... That should give some hints.

> Best regards,
>      Dmitry

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