[GRASS5] Re: r.drain -- new version

Jaro Hofierka hofi at geomodel.sk
Thu Jul 19 05:38:02 EDT 2001

"Roger S. Miller" wrote:

> Rich Shepard wrote:
> >   While I'm on the topic of terrain analysis, let me ask this of the
> > community: why does it appear that so many modules overlap in function? For
> > example, r.slope.aspect, r.drain, r.flow, r.watershed (and others, most
> > likely) all have what appears to me to be either the same functionality (in
> > part), or they are so complementary that they should be aggregated into a
> > single module.
> I wasn't around GRASS at the time the programs were written, so I'm
> probably not the best person to answer this.  But I will anyway.  The
> various modules originated at different times and some from different
> authors.  I suspect that they have never been integrated into a single
> module mostly because noone has ever simultaneously had both the need
> and the time to integrate them.

Hello all,

I think some of these modules (r.watershed, r.fill.dir, r.drain) use older
methods of
flowtracing based on so-called D8 algorithm, i.e. use only limited 8 directions
flow with zig-zag flow pattern. Also, the flowaccumulation is computed using a
flow direction (flow is assigned only to 1 downhill cell).

The second group of flowrouting modules contains r.flow and r.flowmd. They use a
D-infinity algorithm, i.e. consider all possible flow directions and therefore
smooth flowlines.
The flowaccumulation maps are produced using a single flow direction model in
and multiple flow direction algorithm in r.flowmd.

Helena sent me a very interesting link to TerraFlow project at Duke University
(http://www.cs.duke.edu/geo*/terraflow/). Those interested in this topic might
find a
lot of useful information here including comparisons with r.watershed and


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