[GRASSLIST:3015] Re: Vector manipulation

Eric G. Miller egm2 at jps.net
Mon Jan 28 21:52:34 EST 2002

On Mon, 28 Jan 2002 16:44:47 +0100, "M Lennert" <fa1079 at qmul.ac.uk> wrote:

> Emmanuel Poizot <poizot at cnam.fr> wrote:
> > Hi,
> > I'm a newbie in GRASS world.
> > It sems that GRASS better manipulate raster data, however
> > I should like to manipulate vector data, thinks that GRASS seems to do
> > also.
> > I've got some difficulties to find the operations that permits to
> > display
> > a vector with different colors for vectors that have a specific value on
> > a field.
> > I also have some difficulties to find informations that permits me to
> > build and
> > print a map with scale, legend, graticules, etc.
> > 
> > -- 
> > Cordialement
> > 
> Emmanuel,
> I don't know if this would help, but I wrote a little script that allows 
> you to display vector areas in greyscale (sorry, no color, yet) 
> according to defined class boundaries. It uses the latest version of 
> d.area which is in Grass 5.0.0pre3. You can combine this with the 
> PNG driver for map output.
> Usage: d.area.class map=name catfile=name 
> classes=boundary1[,boundary2,..]

Note: I recently added d.vect.area to CVS.  It has a few advantages over
d.area:  (1) it's faster when islands are an issue; (2) it agrees better
with d.vect in world->screen coordinate mappings; (3) output is clipped
to the current region; (4) it accepts a simple legend file format 
(<category> <red> <green> <blue>), with an optional default drawing color
specified with category -1 for drawing categories not in the legend file.

It doesn't yet draw boundary lines, because I wanted to keep the legend
file format simple until we (GRASS developers) implement a more substantial
system for specifying/managing vector drawing styles.  As far as drawing
styles via the values of attribute tables, that probably won't be addressed
in a systematic way until GRASS 5.1 (which will be quite a while).

Eric G. Miller <egm2 at jps.net>

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