[GRASS-user] r.watershed with depressions

[Charles Ehlschlaeger]

The depression map should have ones where there are sinkholes and zeros
where there are no sinkholes. Did your depression map have "no data" at all
other points? If so, that probably caused the problem.

Line 166 of ../src/raster/r.watershed/ram/init_vars.c does not check for no
data values in the depression map (silly of the younger me). It has been too
long since I last wrote code for GRASS to remember how to check for "no
data": that check should be added. Intuitively, "no data" should be treated
as not a true depression in the code. Line 166 should be replaced with the
following code (NODATAVALUE being some variable indicating the no data value
for the depression map):

			if( buf[c] != NODATAVALUE) {
				asp[SEG_INDEX(asp_seg, r, c)] = buf[c];
			} else {
				asp[SEG_INDEX(asp_seg, r, c)] = 0;
			}

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 Carlos "Guâno" Grohmann
Sent: Monday, March 19, 2007 1:44 PM
To: grass user
Subject: [GRASS-user] r.watershed with depressions

Hello all,

I was palying around with r.watershed. If I don't enter a map for real
depressions, it takes about 10 minutes to run, but the streams are not
right. It is a karstic area, so I have some sinkholes, but the streams
do not respect the depressions. So I decided to use the "real
depressions" option. I have a vector layer with points in the
sinkholes, which I converted to raster, with value=1. When I run
r.watershed with this depressions map as an option, it takes about 3
hours to run and the produced maps are entirely NULL.

What is the right way to run this command?

thanks

Carlos

-- 
+-----------------------------------------------------------+
              Carlos Henrique Grohmann - Guano
  Geologist M.Sc  - Doctorate Student at IGc-USP - Brazil
Linux User #89721  - carlos dot grohmann at gmail dot com
+-----------------------------------------------------------+
_________________
"Good morning, doctors. I have taken the liberty of removing Windows
95 from my hard drive."
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