[GRASS-user] Colour problems using r.patch (with OS OpenData)
josh at snorfalorpagus.net
Tue Jan 25 09:32:27 EST 2011
I'm having some difficultly patching together some raster layers (OS
OpenData District Raster - TIFF). Individually, the tiles display
correctly using d.rast. However, if I patch them into a single tile
using r.patch, the colour for all but the first becomes mangled. Example
patching two layers (left and right):
The only reference on the UG I've found is thread:
The issue seems to be something to do with colour tables in the TIFFs
being different. I've not tried the solution provided, as it appears
clunky and I was hoping some progress had been made since '98!
r.in.wms seems to do something like this, patching together tiles
downloaded from a WMS server. I've taken a look at the code for this,
but found it difficult to pick out what is relevant. There is some
mention to using r.mapcalc in a similar way, and also to the GDAL script
gdal_merge.py, which I've not managed to get anything sensible from.
Ideally I'd like to be able to handle these layers from within GRASS
(using pre-existing commands, or a python script) rather than externally
(like gdal_merge.py seems to do), although at this point I'll take
whatever I can get. Can anyone suggest a way forward in this?
Also, as a more general question, does anyone have experience using the
OS OpenData dataset? I'm curious to see what people have done with it
since its release.
Thanks in advance,
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