This is VERY helpful. 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
On Sep 17, 2009, at 12:24 PM, Markus Metz wrote:
Michael Barton wrote:
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.
r.watershed drainage direction is encoded as steps of 45 degree
counted
counterclockwise from East: 1 = 45 degree from East = NE, 2 = 90
degree
from East = N etc. Negative values indicate flow towards a cell with
undefined (NULL) elevation and thus undefined flow accumulation. Cells
with undefined elevation are either outside the current region or
elevation for that cell is not available (MASKed or NULL).
Correlations against an aspect map may not work because in r.watershed
water can flow uphill (hydrological DEM correction on-the-fly). MFD
does
additional corrections to flow direction according to maximum flow,
visible in the difference between SFD and MFD basins (e.g. for
elev_lid792_1m in the North Carolina sample dataset).
Hope that helps,
Markus M
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