[Qgis-user] qgis and big raster catalogs

[Alister Hood]

> Date: Fri, 30 Mar 2012 10:59:09 -0700
> From: Duarte Carreira <DCarreira at edia.pt>
> Subject: [Qgis-user] qgis and big raster catalogs
> To: "qgis-user at lists.osgeo.org" <qgis-user at lists.osgeo.org>
> Message-ID:
>         <19FC4FDFEC50D844B20EB1EF42871FCC2E1B5A5B93 at IE2RD2XVS421.red002.local>
> Content-Type: text/plain; charset="us-ascii"
> 
> Hi Qgisers!
> One question: how to get a fast raster catalog in QGIS with a big number of rasters in it? (in this case 400 ecw)
> I am having trouble getting this to work... I tried a vrt catalog and qgis just hangs when I load it.
> Reducing the number of images makes it ok.
> Is this a know limitation of gdal/qgis? Is there another approach to catalogs (not mosaics)?
> What is the recommended approach to see a large number of images in QGIS when working at big scales (zoomed in)?
> 
> I thought of the following:
> 1-referenced shapefile catalog - like mapserver tileindex shapefiles
> -          Qgis does not support this

Do you mean what I described here?:
http://lists.osgeo.org/pipermail/qgis-user/2012-March/015804.html
Note that if you use an action like I described (instead of using one of the plugins) the exact syntax is probably a little different, depending on what version of QGIS you are running.  I gave the syntax for QGIS master, which enabled the new "expression builder" expressions fairly recently.

> 2-vrt file
> -          Qgis is too slow when there are many images in the catalog
> 3-referenced catalog in some other format? Sqllite?
> -          Couldn't find an alternative
> 4-just load a directory full of rasters
> -          I didn't even investigate this option since I figure this would be painfully slow every time you would load the directory...
> One last detail: I'm using ecw images, but I'm betting this is not format related...