Grass: merging of 2 raster files

Bong Khin Fah bongkf at
Tue Nov 30 19:09:16 EST 1999


I think you might be able to help me.
I have a DEM, and another raster file showing the site boundary polygon,
converted from DXF. I would like to display the DEM in 3D, together with the
boundary outlines.

As Grass d.3d command still does not accept vector draping, my trick is to
merge the DEM and the boundary file into one. However, I guess I must have
use the wrong command cross product, the result has very different colour
for the original DEM. Do you have any idea on how to overlay the two files
in Grass?

Thank you
Khin Fah

----- Original Message -----
From: Michel Wurtz - ENGEES/CEREG <mw at>
To: <grass at>
Sent: Tuesday, November 30, 1999 6:31 PM
Subject: Re: explanation

> Tom Gewecke wrote:
> >
> > I'm trying to combine a vector streams map with a raster relief map, but
> > can't get (after using to work (just get an empty
> > raster).  Can anyone point me to an explanation of how to convert a
> > vector line map like this to raster form?  I assume I have to do this to
> > patch the two together.
> has the "feature" of using the arc attribute as the value
> to fill the right cells on the raster.  If you have not given any
> attribute to an arc, it's like a zero value for the attribute. So
> you trace 0 value vector on a 0 value background... It's exactly
> the same when you have vector polygons.  If they don't have a label
> point, draw nice 0 areas on 0 background (Ah! the perfume
> of invisibility :-)
> How to correct that ? Use v.digit (digitizer: none) on your vector
> file, eventually fill the scale on the header (v.digit won't work
> without the scale specified), chose Label submenu (L), and Bulk
> label remaining lines (B), giving them a value of 1.
> Quit v.digit, run, then, and you will see your
> lines as cell values "1", the background remaining "0".
> --
> Michel Wurtz    ENGEES - CEREG
>                 1, quai Koch - BP 1039, F-67070 STRASBOURG cedex
>                 Tel: +33  Fax: +33

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