[GRASS-user] Directed vector networks (e.g. river networks)

[Johannes Radinger]

On Fri, Jun 14, 2013 at 11:59 AM, Markus Metz <markus.metz.giswork at gmail.com
> wrote:

> On Fri, Jun 14, 2013 at 11:03 AM, Johannes Radinger
> <johannesradinger at gmail.com> wrote:
> > Hi,
> >
> > as I am not very familiar with GRASS' vector capabilities maybe someone
> of
> > you has some ideas. Is there the concept of directed vector networks e.g
> > describing river networks with flow direction implemented in GRASS?
>
> r.stream.extract produces a vector network with the direction of the
> lines corresponding to the flow direction.
> >
> > I am looking for a way that counts all barriers when routing from a
> starting
> > point in the network And I'd like to get the number of barriers that are
> > downstream and those that are upstream a given point. Or is there a way
> to
> > "cut" a network into two parts where one is automatically detected as
> > upstream while the other one is declared as the downstream network?
>
> Maybe the linear referencing system can help to count barriers.
>
Thank your for that info. I am totally unfamiliar with the LRS system, so
I'll look into
that and do some reading... :)


>
> For separate upstream/downstream analysis, you could use vector
> network analysis tools and make use of the line direction: if want to
> go only upstream, set forward costs to -1, if you want to go only
> downstream, set backward costs to -1.
>
> What tool of vector network analysis tool are you thinking of? can you
given an
example, e.g. to extract the enitre network upstream a given point?



> >
> > Furthermore I am interested in calculating stream order for such
> dendritic
> > networks. I saw the v.strahler add on, is there also an add on that
> > calculates other types of stream order (here I am most interested in a
> > vector based Shreve's stream order like as already implemented in
> > r.stream.order).
>
> You could use r.stream.extract to produce both a raster and a vector
> river network, then run r.stream.order on the river raster and update
> the attributes of the vector with the desired order using v.what.rast.
>

Yes I also thought of using the really nice r.stream.* toolbox, although it
is
somehow inconvinient to transform to and from raster/vector just to get the
network topological factor "stream order". Theoretically, from a directed
e.g. stream
network that does not include "cycles" it should be possible to generate a
stream
order map, but probably that needs quite some knowledge abouot GRASS'
network
system and programming skills. Maybe a future add-on :)

/Johannes


> HTH,
>
> Markus M
>
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