[GRASS-user] Reverse flow accumulation

[Charles Ehlschlaeger]

Flipping the DEM may not always provide desired results. 

On the other hand, if you use r.cost with the start_site is the "given
pixel", then use r.drain with the site as the outlet point, r.drain's output
map will contain the grid cells that travel from the "given pixel" to the
outlet point inclusive. The result will be a single pathway, however.
Riparian areas are not often so.

Sincerely, chuck

Chuck Ehlschlaeger, Associate Professor & GIS Center Director
Department  of  Geography,      Western  Illinois  University
215 Tillman Hall,   1 University Circle,  Macomb,  IL   61455
cre111 at wiu.edu,    phone: 309-298-1841,     fax: 309-298-3003

-----Original Message-----
From: grassuser-bounces at grass.itc.it [mailto:grassuser-bounces at grass.itc.it]
On Behalf Of Sitansu B Pattnaik
Sent: Thursday, April 05, 2007 1:16 PM
To: grassuser at grass.itc.it
Subject: RE: [GRASS-user] Reverse flow accumulation

You could just flip the DEM and then recalculate Flow accumulation.
Sitansu

-----Original Message-----
From: grassuser-bounces at grass.itc.it [mailto:grassuser-bounces at grass.itc.it]
On Behalf Of Jonathan Greenberg
Sent: Thursday, April 05, 2007 12:28 PM
To: grassuser at grass.itc.it
Subject: [GRASS-user] Reverse flow accumulation

Typically flow accumulation tracks the number of pixels that are uphill of a
given pixel, but is there anyway to track the number of pixels that are
DOWNHILL of a given pixel (e.g. to the drainage outlet)?  The reason I ask
is that I'm dealing with a riparian bathymetry dataset which does not
encompass the entire watershed although it does include the outlet as well
as an unbroken, continuous distribution of values upstream from that point
until it terminates at an arbitrary boundary, but I want to have a proxy of
the flow to those points.  Uphill accumulation will not work because the
"origin" of the streams is completely arbitrary (e.g. I can't just assign
them a value of "0" at the edges).

Thoughts?

--j

--
Jonathan A. Greenberg, PhD
Postdoctoral Scholar
Center for Spatial Technologies and Remote Sensing (CSTARS) University of
California, Davis One Shields Avenue The Barn, Room 250N Davis, CA 95616
Cell: 415-794-5043
AIM: jgrn307
MSN: jgrn307 at hotmail.com



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