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

[Phillip Allen]

Moritz,

My intention for these overlapping polygons are:
1. Sort them decreasing in area (so the big basins plot below the smaller
ones) and use them for symbolization.
2. Spatially join data to the stream sediment samples.  Which sample are
below know gold/copper/silver/zinc/lead/etc mines, which are below
towns/villages, land use, etc.
3. Cut the basin polygons using a geological polygon map and and calculate
km2 or percentage of km2 for each lithological unit found within each
basin.  After denormalizing these areas & lithologies (rows as samples and
the columns km2 of each lithology) one can then perform linear regression
models on the chemical analysis.

regards,
Phil




On Wed, Oct 26, 2016 at 9:18 AM, Moritz Lennert <
mlennert at club.worldonline.be> wrote:

> Le Wed, 26 Oct 2016 08:37:38 -0600,
> Phillip Allen <phillipjallen830 at gmail.com> a écrit :
>
> > 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.
> >
> > 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!
>
> See Markus Metz' answer in a similar thread from two days ago:
>
> http://lists.osgeo.org/pipermail/grass-user/2016-October/075475.html
>
> As in his message: it is possible to handle overlapping polygons using
> cat numbers, but the first question is: what do you want to do with the
> data ?
>
> Moritz
>
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