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

[Dmitry Baryshnikov]

02.02.2012 18:10, Andrea Peri ?????:
>
>
> 2012/2/2 Even Rouault <even.rouault at mines-paris.org 
> <mailto:even.rouault at mines-paris.org>>
>
>     Selon Andrea Peri <aperi2007 at gmail.com <mailto:aperi2007 at gmail.com>>:
>
>     > Hi,
>     >
>     > Unfortunately I was unable to test with GDB.
>     > My skill was not enough :(
>
>     Well, provided you have gdb installed, it is "just" a matter of :
>
>     1) "gdb qgis"
>     2) in the gdb console, type "run" and validate
>     3) when qgis is slow, switch to the console with gdb and hit Ctrl+C
>     4) in the gdb console, type "bt" (for backtrace)and validate, and
>     then it can
>     give some interesting information
>     5) to go on qgis execution, type "c" (continue) and validate
>     6) you can go to 3) again
>
>
> thx, I try it .
>
>     >
>     > However I try other ways
>
> >
>
>     .....
>
>     > So qgis necessary must open all the raster to understand what
>     raster is on
>     > the visible portion on the canvas.
>
>     No, what you show above is sufficient to defer the loading of
>     individual tiles,
>     until they are really necessary.
>
>     What I suspect is that your vrt has no associated overviews, so
>     when you open
>     qgis, it will try to display the overall coverage of the raster,
>     which then will
>     require to open each tile.
>
>     Try "gdaladdo your.vrt 2 4 8 16 32"
>
>
> I try to create the overview, but it is really sloow .
> After 1hours is to 0%.
>
> I will try with a selection of few rasters.
>
>
>     >
>     > I guess this is a good reason to explain because it is so slow
>     when in the
>     > catalog there and many hundred of rasters.
>     >
>     > Unfortunately I don't find any option in gdalbuildvrt to add the
>     extension
>     > of every raster in the catalog.
>
>     There's none : the above information that is generated by default
>     is sufficient.
>
>
> Sorry Roualt,
> the catalog give the start point and the number of pixel , but miss 
> the size in meters or "unit of map" of every pixel so for me was not 
> possible to detect the bbox of every raster.
> Perhaps in the overview there is the missing information ?
>
> >Best regards,
> >
> >Even
>
> Thx,
> Andrea.
>
>
> -- 
> -----------------
> Andrea Peri
> . . . . . . . . .
> qwerty àèìòù
> -----------------
>
>
>
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We have discussed this problem with Even. I'll fix it. The work is in 
process.

Best regards,
     Dmitry
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