[Qgis-user] Batch conversion of rasters

[benoit-3 at bc-consult.com]

Hi, 

On 17.05.2012 11:52, giannis Nj wrote: 

> I want to convert
a directory with .asc files to .tiffs, but I need the output files to
have the same colour analysis, as when they are already loaded in qgis
display. I try Raster->Conversion->Translate (Convert format) but it
gives each file with different colours. Is there any other way to make
it? Maybe a batch convert somehow after the files are loaded on
screen?

(1) Do you want to embed the colour table into the tiff files?
Or 

(2) Do you want to carry over (keep) the 'true' values of the asc
files in the tiff files? 

Answer for (2): 

If you want to keep the
true values, then I suggest that you save a .qml file (raster properties
-> Save Style...) for each .asc file displayed in QGIS (use the same
filename as the asc file). Then, use the same file name for the tiff
files as well, and put them in the same folder as the qml files and open
them in QGIS. 

e.g. file1.asc -> file1.qml, then convert "file1.asc" to
"file1.tiff" and make sure both .tiff and .qml files are in the same
folder.
When you load the .tiff file in QGIS it will also load the style
from the .qml so that the .tiff and .asc files will display identically.


Note: to save a full bunch of qml at once you can use the "Save
default QML" plugin available from GIS-Lab repo at [0], or,
alternatively, the "Save QML" plugin available from [2]. 

Answer for
(1): This is far more complicated! 

Two leads to possibly solve this
problem: 

- Tim Sutton's blog about using GDAL to embed colour table in
raster at [1]. 

- Use the "One-band raster to paletted or RGB" plugin
(V0.3.0) from this repo [2].
 See the help page at [3]. 

Anyway, you
will have to use scripting if you have many files to process. 

[0]:
http://gis-lab.info/programs/qgis/qgis-repo.xml
[1]:
http://linfiniti.com/2011/12/creating-coloured-rasters-with-gdal/
[2]:
http://www.bc-consult.com/free/plugins.xml
[3]:
http://www.bc-consult.com/free/bccAddRColor.html 

HTH,
Benoit 

  
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