180 degree offset of r.slope.aspect (& now s.surf.tps)

[Jianping Xu]

I used the r.mapcalc to obtain a "true azimuth" map which starts 
with due N and from ZERO, and goes clockwise:
	r.mapcalc new_aspect = '(24 + 7 - old_aspect)%24'

If you would like the N to be value ONE, you may use:
	r.mapcalc new_aspect = '(24 + 8 - old_aspect)%24'

The only problem is no data (0) and flat (25) will also be transferred 
to some "real" aspect values. However it's effect will be very minor
since an aspect value is only significant when the slope is not zero.

Jianping Xu
Rutgers University
Cook College Remote Sensing Center
New Brunswick, NJ 08903-0231
(908)932-9631 email jianp at ocean.rutgers.edu