r.slope.aspect

[Lachlan Bruce]

I am using r.slope.aspect to reduce the possible 360 degrees of aspect down to 8 principle directions (N,NE,E,etc). When running the program r.slope.aspect interactively, the header tells me that the aspect output will be categorised into 24 directions, as does g.manual. However, the output is in 360 categories. 

My questions are:

Have I got a new/old version of r.slope.aspect or is there something I do to get just 24 categories, not 360?

If I have to live with 360 different categories, is there an easy way to reduce this down to 8 categories without having to laborously use r.reclass?

The output from r.slope.aspect is below...



OUTPUT......  


SLOPE and ASPECT

This program produces aspect and slope maps from elevation data.
The elevation layer must be true elevation values, not rescaled.
The aspect map will indicate the direction of the slopes in 24
directions.  The slope map will have slopes in degrees.
Please enter the elevation file, and the names for the resulting
aspect and slope maps.
 
enter elevation file
Enter 'list' for a list of existing raster files
Enter 'list -f' for a list with titles
Hit RETURN to cancel request
> c.asp
<c.asp>

enter aspect file
Enter 'list' for a list of existing raster files
Enter 'list -f' for a list with titles
Hit RETURN if you don't want this product
> c.asp.24
<c.asp.24>

enter slope file
Enter 'list' for a list of existing raster files
Enter 'list -f' for a list with titles
Hit RETURN if you don't want this product
> junk
<junk>
Do zero values in the elevation map represent true elevations? (y/n) n
Should the slope be reported in percentage of growth instead of degrees?(y/n) y
percent complete:  100%
CREATING SUPPORT FILES
ELEVATION PRODUCTS for mapset [lachlan] in [acheron]
360 cats of aspect
Color table for [c.asp.24] set to aspect
ASPECT [c.asp.24] COMPLETE
87 cats of slope
SLOPE [junkformat=perc] COMPLETE



Thanks.

Lachlan Bruce


    _/      _/   _/_/_/_/    _/_/_/_/        Lachlan Bruce
   _/  _/  _/  _/          _/      _/        Water Studies Centre
  _/ _/_/ _/   _/_/_/_/   _/      _          Monash University
 _/_/  _/_/          _/  _/      _/          Melbourne   AUSTRALIA
_/      _/   _/_/_/_/     _/_/_/_/   e-mail: lachlan at gis.wsc.monash.edu.au