31.01.2012 18:32, Even Rouault пишет:
Selon Dmitry Baryshnikov<poli...@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
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.
Best regards,
Dmitry
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