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Is there a way to export all values from a raster to for example a cvs or other textfile or dbf or xls and later import (changed) values from that file back into the raster? For vector-files this is no problem but for raster-files I have not found anything like this. (Important here: the export-file should be a table, not a grid).

The idea is to process raster-data with some external program like excel of statistics-software, to add channels (=columns) based on the data already there or create a new channel by linking data with data from a table. All this can be easily done for vector-layers but apparently not for raster-layers.

THX, stn

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2 Answers

As mentioned in the other topic, you could use gdal2xyz. For each pixel in a raster this will save an xyz triplet in a CSV text file. It's included with the GDAL that comes with QGIS, run it from an OSGeo4W command line window:

gdal2xyz -csv infile.asc outfile.csv

Under Linux you could try running it in a terminal. If this doesn't work 'locate' gdal2xyz.py and add its path to the command line. It will work with one-band rasters in all of the common formats, not just ASCs. Come back if you have rasters with more than one band, gdal2xyz can handle these too.

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Oops, forgot about that one :-) Yes, that solves part of the problem. Now I only have to get the data back in after external processing, along with the original coordinates, datum etc. One thing surprised me: Why does gdal2xyz handle only one band at a time? It could just as well output x and y and one addtional column for each band. –  stn Apr 3 '12 at 18:54
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OK, so gdal2xyz does handle multiple bands. You find that out after googling: gdal2xyz -band 1 -band 2 scrfile.tif –  stn Apr 3 '12 at 19:24
    
Yup! It will even handle images. You have to drop the -csv if there is more than one band and then you get a space-delimited text file. –  nhopton Apr 3 '12 at 19:54
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Well, here is a nice twist :-)

The latest version of GDAL includes a program named "gdal_calc.py" that looks like it can do more on the commandline than the version that is in the QGIS-menu. Very cool !

With Ubuntu this tool does not show up unless you completely uninstall the "stable" version of QGIS and all its dependencies and then reinstall from the "unstable" repository.

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