[GRASS-dev] r.watershed question

[Jarek Jasiewicz]

negative numbers are assigned to cells which contribute outside area
numbers refers to direction:
 
3 | 2 | 1
 --- --- ---
 4 | 0 | 8
 --- --- ---
 5 | 6 | 7

you can find direction by multipy the number by 45 (against east CCW)

from help page:

/drainage/
    Output map: drainage direction. Provides the "aspect" for each cell
    measured CCW from East. Multiplying positive values by 45 will give
    the direction in degrees that the surface runoff will travel from
    that cell. The value 0 (zero) indicates that the cell is a
    depression area (defined by the depression input map). Negative
    values indicate that surface runoff is leaving the boundaries of the
    current geographic region. The absolute value of these negative
    cells indicates the direction of flow. 

Jarek

Michael Barton pisze:
> r.watershed can produce a map of "drainage directions".
>
> The values of a direction map are in the range of -8 - +8
>
> Can someone tell me what these numbers refer to? That is, what 
> direction is 3 or -3? I've tried to run some correlations against an 
> aspect map and am not getting meaningful results yet.
>
> Thanks
> Michael
>
>
> ____________________
> C. Michael Barton
> Director, Center for Social Dynamics & Complexity
> Professor of Anthropology, School of Human Evolution & Social Change
> Arizona State University
>
> Phone: 480-965-6262
> Fax: 480-965-7671
> www: www.public.asu.edu/~cmbarton, http://csdc.asu.edu
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