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
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
_______________________________________________
grass-dev mailing list
grass-dev@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-dev
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
Thanks much. I swear I looked at the help file but somehow did not see this.
I appreciate your help.
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 12:14 PM, Jarek Jasiewicz wrote:
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
_______________________________________________
grass-dev mailing list
grass-dev@lists.osgeo.org
grass-dev Info Page
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