[GRASS-user] r.terraflow -> streams ?

[Dylan Beaudette]

On Wednesday 17 May 2006 00:42, orkun wrote:
> Dylan Beaudette wrote:
> >On Tuesday 16 May 2006 02:59, orkun wrote:
> >>hello
> >>
> >>can I  produce stream map using r.terraflow maps ?
> >>
> >>regards
> >
> >here is one such example:
> >
> >http://casoilresource.lawr.ucdavis.edu/drupal/node/166
> >
> >cheers,
>
> thank you
>
> I looked the site you directed me.
> Compared to r.watershed, r.terraflow produced stream map much faster. But
> there  seems to be broken streams. Although I lowered the accumulation
> threshold value, broken streams still exist.
> How can I get unbroken streams using r.terraflow.

Hi,

You could try computing the line lengths, and throwing out features that are 
less that a given length:

v.to.db ...
v.extract ...

Or.. it would be even better to characterize stream networks according to 
their "order" , based on the number of contributaries feed into the main 
channel. Then, keep all streams of order _n_ or greater.

> Since I worked on DEM quality, I saw some interesting features
> in the other part of the site. Does "DEM vs. Field Slope" show
> DEM's quality.

I think that you might be referring to this image:
http://casoilresource.lawr.ucdavis.edu/drupal/node/189?size=_original

The title is a little confusing, as it is a comparison between slope values 
measured in the field with a clinometer compared with slope values computed 
from a DEM via r.slope.aspect . The take-home message from that graph was 
that the DEM-computed slope values tended to under estimate field measured 
values [1]. Also that a comparison between DEM and field slope seemed to work 
best when comparing average slope within a 20 meter radius as compared to 
using the DEM derived slope value at the exact location of the field 
measurement. 

[1] note that field measurement of slope is not an exact science, and is 
certainly not conducted at the same scale at which the DEM for this area was 
created (10 meter grid) .

Cheers,

-- 
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341