There are several ways to do this in GRASS.
This is most generically handled by d.rast.arrow. This routine will draw arrows within (preferably coarse, as you suggest) raster grid cells indicating the 'downslope' direction of an aspect grid cell. You can theoretically define any raster directional vector as an aspect map and do the same.
Another way is to use r.direct, which creates a flow-direction map from any 'elevation' surface. Again, you can define any conceptual surface as an elevation map in this case. Several of the watershed analysis/modeling routines also generate flow-direction maps as part of their outputs.
Michael Barton
On Friday, April 2, 2004, at 12:58 PM, grass5-request@grass.itc.it wrote:
Subject: display of vector fields
Platform: GNU/Linux/i386
grass binary for platform: Compiled from Sources
GRASS Version: 5.0.2It would be nice to have a display module for vector fields:
it takes two rasters as arguments (one for direction, one for magnitude), and it
draws arrows representing the direction and magnitude at each point (probably
only good for low resolution rasters).
That way you could use it to get a nice visual representation of wind or water
flow, and similar things.
It might also be a good thing to add the resolution drop into the program (instead
of depending on low resolution rasters) so that you could display a relatively high
resolution DEM and then overlay a vector field representing water flow (or wind,
or whatever) at a lower resolution so that there's room to draw the arrows without
them interfering with each other-------------------------------------------- Managed by Request Tracker
______________________________
Michael Barton, Professor & Curator
Department of Anthropology
Arizona State University
Tempe, AZ 85287-2402
USA
voice: 480-965-6262; fax: 480-965-7671