[GRASS-user] Aspect direction in r.slope.aspect

[Hamish]

Bob Moskovitz wrote:
> I was just wondering why aspect is measured from the east
> and increased counterclockwise instead of the north and
> clockwise?  It seems to run counter to what is done in other
> GISs.


It is just measuring theta positive from the x-axis, in the mathematical
sense.

It stays like that for historical reasons, probably been that way for 20+
years. (aka we can only guess at the original logic)

Convert between that and the compass (CW from north) convention with
"90 - angle". Most modules which deal with aspect maps should already
have an option to read the different type.


Hamish