[Qgis-user] is it possible to group rasters?

[Mike Toews]

On 2010-01-15 03:23, M.E.Dodd wrote:
> I have not tried this, will do (will also look at earlier suggestion of combining them in Grass), however it will still be very slow if you have 50 raster tiles as I have, would have thought it a very obvious thing to want to have all tiles treated the same easily.
> For example the tiles are from a digital elevation model so I want to try different max and min values to see which is most appropriate over the whole area, its extremely laborious to go through keep changing every one of the 50 tiles again and again just to find the best compromise.
>    

I generally make a mosaic or merge DEMs (or other continuous rastes) 
using the tools provided by the gdal-python package. E.g., in a shell 
(*nix or OSGeo4w):

gdal_merge -o bigDEM.tif 094*dem

where 094a.tif, 094b.tif, etc. are the input tiles (I use wildcards here 
for convenience of grouping the tiles), and bigDEM.tif is the output 
raster, which you can then open in any GIS program.

http://www.gdal.org/gdal_merge.html

-Mike