[GRASS-user] Non-Topological Vector Polygon Layer From r.water.outlet

[Markus Metz]

On Wed, Oct 26, 2016 at 4:37 PM, Phillip Allen
<phillipjallen830 at gmail.com> wrote:
> Hi,
>
> I have a point layer file that represents stream sediment sample locations.
> My goal is to create watershed basins for each sample location using
> r.water.outlet or r.stream.basins, then convert to a vector layer and
> finally have them reside in a PostGIS table with all the other associated
> sample data. I have run the points through r.stream.snap so they now fall
> exactly only the DEM drainage.
>
>
> Grass normally operates with topology but in this case I need a
> non-topological vector polygon layer. Stream sediment samples are often
> collected every 1-5km or more along any particular drainage so the basins
> must overlap.

IOW, you need the complete basin for each sample location? In this
case you would need to run r.water.outlet or r.stream.basins for each
sample location separately, that is, loop over the sample locations
and perform the desired analysis for each sample location separately.
Any subsequent statistical analysis might need to consider that
different basins overlap (pseudo-replication).

Markus M

>
> What is the best strategy to deal with generating an overlapping polygon
> layer? I have only approximately 10,000 stream sediment samples this time
> but there are always more!
>
> I have been programming in R for so many years my python has deteriorated to
> nothing…..
> regards,
>
> Phil
>
>
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