DESCRIPTION
d.rast.arrow
is designed to help users better visualize surface water flow direction,
as indicated in an aspect raster map layer. There are two ways to specify
the aspect layer the program is to use. The first is to display the aspect
map layer on the graphics monitor before running d.rast.arrow.
The second method involves setting the map parameter
to the name of the desired aspect map.
This allows the arrows to be drawn over any other maps already displayed
on the graphics monitor.
d.rast.arrow will draw an arrow over each displayed cell
to indicate in which direction the cell slopes.
An arrow can point in one of eight directions. If the aspect
layer has a category value denoting locations of "unknown" aspect,
d.rast.arrow draws a question mark over the displayed cells
of that category.
Cells of containing null data will be marked with an "X".
NOTES
Arrows are drawn at the size of a cell and cannot be seen if the raster map is
relatively close in scale. From a command line mode, the user cannot run
d.rast.arrow and then run d.zoom
and still see the arrows. The zooming action erases the arrows and the user
must run d.rast.arrow again.
GRASS aspect maps are measured in degrees counterclockwise from east. i.e.:
90 North
180 West
270 South
360 East
They can be created from a raster elevation map with r.slope.aspect.
SEE ALSO
d.frame
d.rast
d.rast.edit
d.rast.num
d.zoom
g.region
r.mask
r.slope.aspect
parser
AUTHOR
Chris Rewerts,
Agricultural Engineering,
Purdue University
Last changed: $Date$