Assuming you have a raster with a sufficiently high resolution to ID the banks (e.g., 30m is probably too coarse for most cases), try one of the following.
Create a buffer that just includes the banks and make it a MASK, create a map of profile curvature (in r.slope.aspect), run r.neighbors with the max filter on the the profile curvature map with the MASK on.
You could also create a sequence of points that represents the river channel (e.g., do r.watershed and output the streams, turn the stream cells to vector points); run r.cost with the stream points as the starting vector. Then you can query the cost map to see where it has a jump in cost around the river. You could also do a slope of the costs and then run a max filter on the cost slope map to ID the zones where cost shows the steepest increase.
Michael
____________________
C. Michael Barton
Director, Center for Social Dynamics & Complexity
Professor of Anthropology, School of Human Evolution & Social Change
Arizona State University
voice: 480-965-6262 (SHESC), 480-727-9746 (CSDC)
fax: 480-965-7671 (SHESC), 480-727-0709 (CSDC)
www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu
On Oct 19, 2011, at 12:00 PM, <grass-user-request@lists.osgeo.org> wrote:
Message: 7
Date: Wed, 19 Oct 2011 15:50:20 +0200
From: Markus Metz <markus.metz.giswork@googlemail.com>
Subject: Re: [GRASS-user] Is it possible to derive both banks of a
river ?
To: Pankaj Kr Sharma <pkscwc@gmail.com>
Cc: grass-user@lists.osgeo.org
Message-ID:
<CAG+h=FHK-MGwwnhhc8_-p=RPR9QRjXgwFxfjUnbY8Y8JK8PDEQ@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1On Tue, Oct 18, 2011 at 10:12 AM, Pankaj Kr Sharma <pkscwc@gmail.com> wrote:
Dear friends,
I derived this accumulation map from 90m srtm data.
Across the river, the accumulation varies and the river line passes through
the maximum of these values.Typical Scenario:
On right bank Acc= 3
Near Right Bank?? Acc=100000
____________________________________
??? |
-.-.-.-.-.-.-.-.-.-.-.-.-|.-.-.-.-.-.-.-.--.-.-.-.-.-.-.-.-.- ? ?? on river
line Acc=500000 ? ? ? -->
_______________|_____________________Near left Bank Acc=300000
On left Bank Acc = 2
i.e. Just at the banks, accumulation values have big difference.
Whether this fact can be utilised to derive both banks of a river network.
You could try to calculate slope with the flow accumulation map and
then identify river banks as cells with high slope and low flow
accumulation.Just an idea,
Markus M