[GRASS-user] minimum basin size for output from r.terraflow

[Hamish]

Dylan Beaudette wrote:

> On the topic of watershed basin delineation...
> 
> In preparing a small demo for my labmates, I was asked about the best
> way to  delineate watershed basins at various scales with an algorithm
> like  r.terraflow. With r.watershed, it is possible to define a
> minimum basin size,  which can act as a scaling parameter. As a quick
> hack, I attempted to  replicate this by vectorizing the output from
> r.terraflow and then using  v.clean to remove basins smaller than some
> threshold. The results were  largely similar to the basins produced by
> r.watershed, but in some cases the  purely vector-based approach to
> "scaling" the basins resulted in questionable  output (not
> surprisingly). 
> 
> So is there any logical way to define a minimum basin size for modules
> like  r.terraflow - or does that construct even make sense for such
> algorithms [1].
> 
> 1. noting that the concept of a watershed basin actually occurs at all
> scales,  and is most likely fractal in nature.


it is hierarchical, you have to disolve the correct boundary.

I too find this to be an interesting question (and have r.terraflow
watersheds waiting to be reduced).

idea:
Find center of small vector areas (use centroid) and apply r.drain to
see if they are connected, then reassign cat to larger area's cat and
"v.extract -d"?


r.flow ?
r.water.outlet ?
new raster module?


Hamish