[GRASS-user] Multiple usage of r.water.outlet

[Christian Schwartze]

Yes, thats right, and I tried this with g.region zoom=basin<x> for example. But
I have to merge more than one area and they could be distributed far away each
other, in worst case.

Regards,
Christian.

Zitat von Michael Barton <michael.barton at asu.edu>:

> If you run g.region to set the computational region to just the area of each
> basin before doing the other calculations, it might run a lot faster.
>
> Michael
>
>
> On 5/15/08 5:02 AM, "grass-user-request at lists.osgeo.org"
> <grass-user-request at lists.osgeo.org> wrote:
>
> > Date: Thu, 15 May 2008 14:00:14 +0200
> > From: Christian Schwartze <Christian.Schwartze at uni-jena.de>
> > Subject: [GRASS-user] Multiple usage of r.water.outlet
> > To: grass-user at lists.osgeo.org
> > Message-ID: <1210852814.482c25ceebafb at webmail.uni-jena.de>
> > Content-Type: text/plain; charset=ISO-8859-1
> >
> > Dear GRASS user,
> >
> > the problem I have is using r.water.outlet for some scripting in Python.
> Below
> > I
> > want to explain the proceeding in detail. It should be mentioned in advance
> > that
> > the necessary drainage raster has nearly 10000 rows and columns, so it's
> not
> > really small...
> > I have a point shape file (or generally point coordinates, more than 100
> > pairs)
> > that presents the input for multiple calls of r.water.outlet. To produce a
> map
> > representing the corresponding watersheds of all these points I thought of
> the
> > three following approaches:
> >
> > (A)  At certain intervals (of the r.water.outlet iteration) I sort the
> > previous
> > calculated basins by area and use the resulting and ascending order as an
> > input
> > for r.patch. So the basins can not hide each other.
> >
> > (B) At certain intervals I execute r.cross for overlaying the previous
> basins.
> >
> > (C) I use r.mapcalc in every iteration step with an expression like
> > "allbasins = allbasins +
> >
> if(isnull(allbasins),basin<x>,if(allbasins>=1&&basin<x>==1,<newBasinID>,allbas
> > ins))"
> > where allbasins is initially a "novalue" raster.
> >
> >
> > All methods above are working right, but have the same lack: the
> performance -
> > too slow!
> > Remember that the working raster has an extent of 10000x10000 pixel. The
> > single
> > calculated basins and their extents compared to entire drainage raster are
> > very
> > small (see the attachment). While the duration of r.water.outlet is barely
> > acceptable, the merging step (regardless of the technique in A, B or C)
> takes
> > too long.
> > What do you think about the three approaches for a script in Python and how
> > can
> > i minimize the performance problem when bringing the basins together within
> a
> > large area? Many thanks for any advice!
> >
> > Regards,
> > Christian.
>
> __________________________________________
> Michael Barton, Professor of Anthropology
> Director of Graduate Studies
> School of Human Evolution & Social Change
> Center for Social Dynamics & Complexity
> Arizona State University
>
> phone: 480-965-6213
> fax: 480-965-7671
> www: http://www.public.asu.edu/~cmbarton
>
>
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