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

[Andrea Peri]

2012/2/2 Even Rouault <even.rouault at mines-paris.org>

> Selon Andrea Peri <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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