[GRASS-user] Why r.watershed Yields Narrow Basins

[Rich Shepard]

On Sun, 10 Jun 2012, Markus Metz wrote:

> These nearly straight red lines indicate that the DEM is flat in these
> areas.

Markus,

   These are mostly the valleys on either side of the mountains.

> What kind of pre-processing did you apply?

   None.

> Also, to reproduce the results, the output of r.info of the DEM, g.region
> and g.proj would be helpful.

g.region -ap rast=dem_proj
projection: 99 (Transverse Mercator)
zone:       0
datum:      nad83
ellipsoid:  grs80
north:      28704673.96487485
south:      28563905.79283388
west:       464582.93917488
east:       628305.08857358
nsres:      29.98895868
ewres:      30.00222639
rows:       4694
cols:       5457
cells:      25615158

g.proj -p
-PROJ_INFO-------------------------------------------------
name       : Transverse Mercator
proj       : tmerc
datum      : nad83
ellps      : grs80
lat_0      : 34.75
lon_0      : -115.5833333333333
k          : 0.9999
x_0        : 200000.00001016
y_0        : 8000000.000010163
no_defs    : defined
-PROJ_UNITS------------------------------------------------
unit       : US survey foot
units      : US survey feet
meters     : 0.3048006096012192

r.info map=dem_proj
Layer:    dem_proj                       Date: Fri Mar 16 17:00:56 2012
DataBase: /home/rshepard/grassdata
Title:     ( dem_proj )

Type of Map:  raster               Number of Categories: 255
Data Type:    FCELL
Rows:         4694
Columns:      5457
Total Cells:  25615158
Projection: Transverse Mercator
N: 28704673.96487485    S: 28563905.79283388   Res: 29.98895868 |
E: 628305.08857358    W: 464582.93917488   Res: 30.00222639
Range of data:    min = 1654.234  max = 3143.268

Data Description:
generated by r.patch
Comments:
r.patch input="dem2,dem3" output="dem_proj"

Rich