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

Even Rouault even.rouault at mines-paris.org
Tue Jan 31 10:20:21 EST 2012

> >
> Hi, Even
> I faced this problem before. I checked under debugger and saw that vrt
> sources were not creating overviews. So, gdal was making long RasterIO
> executions to the source raster, but not overviews. I provided a patch
> which took the overviews from origin raster and wrapped them too. May be
> this is not so elegant solution, but it works and speed up work with
> wrapped rasters considerably.
> I don't thik that qgis under GDB/DDD will give any additional
> information (one will just see long RasterIO executions).
> But I can still try to use GDB if you think this might help.


I don't deny the problem you describe. And your solution sounds reasonable. But
without more precise context from Andrea, I just wanted to be sure that it was
the precise case that Andrea ran into. There might be other issues involved
(like histogram or statistics computations that can take a long time, but
admitedly, I wouldn't expect the VRT overhead to be significant) and displaying
the stack can show which first GDAL API call is involved.

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