[GRASS-user] Use variables in GUI?

Hamish hamish_b at yahoo.com
Thu Sep 23 21:43:46 EDT 2010

Richard wrote:
>  This may be beyond Grass-GIS, but here goes.

nothing is impossible :-)

> I have to generate many output maps (50) and I need
> transparency - which means I can't just use d.vect and
> d.out.file in a script.

i.e. you need blending? that is done for the GUI by the g.pnmcomp
Use the PNG driver (it is map filename extension aware to avoid .png)
or d.out.file to create the files. or just use NetPBM's version of
pnmcomp yourself.

> But in the outputs, I have to restrict the display to a
> named area (eg: state="NSW").
> So I'm wondering - is there any way within the GUI - either
> TCL or Python - to use a variable within the SQL query?
> That way, it may show "state=$variable" in the select
> window, and I just need to set the variable, zoom to a
> region, and produce an output rather than having to adjust
> the variable in 50 or so outputs!

my only idea would be to write a script which created a GUI session
file dynamically, then load those.  but g.pnmcomp could bypass the issue?

Also of note, r.out.png in 6.5svn has a new -t flag to make the NULL cells
transparent, and a new -w flag to output a world file. r.out.tiff will get
the same for NULL cells at some point. The main reason for this is that it
makes nice rasters for WMS, TMS, gdal2tiles & OpenLayers web maps. I see
no reason why these shouldn't be backported to 6.4.1 after some quick
testing in 6.5.  (trac #1077)



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