[GRASS-user] Re: highest and lowest point in catchment

Fri Feb 8 16:33:02 EST 2008

Just another (incomplete) idea!

On Fri, 2008-02-08 at 10:19 -0200, Daniel Victoria wrote:
> Maybe something like this...
> 
> For each catchment you run r.info -r to get the highest and lowest
> value of the DEM (use a MASK for the catchment and r.info -r DEM).
> 
> Then, with r.mapcalc you select the highest and lowest areas that you
> obtained with r.info.

(a) Here "r.stats -ng" to get pixel values with coordinates (?) and
export in file (like x,y,z)

(b) Do a numeric sort (sort -n) according to z value

sort -n -k3 input_file.txt | tail -1   #### this is from
http://lists.osgeo.org/pipermail/grass-user/2008-January/042520.html

(c) Instead of only tail -1	grab both "head -1" (that would be the min)
and "tail -1" (that would be the max) and so you have one "min" and one
"max" even if you have small areas 

and then the rest... (?)

>  After that you can vectorize the areas selected
> and do v.db.update to get coordinates.
> 
> It would be nice to put this all into a script if you have too many catchments.
> One problem would be that you might not get a single pixel for the
> high and low parts of the basin. It could be a small area...
> 
> Another thing. v.rast.stats can give you the max and min value for a
> DEM for every catchment. It just wont give you the coordinates - not
> that I know of...

> 
> Good luck
> Daniel
> 
> On Jan 30, 2008 5:03 AM, Dr. Manuel Seeger <seeger at uni-trier.de> wrote:
> > Thanks Richard,
> > but elevation data is on a raster map.
> > The idea I had was to generate point vector files with the highest and
> > lowest point and then generate the colums with y and y coordinates...
> > but it seems to me like a complicated way and I was wondering if there
> > is a possibility to do that with r.mapcalc.... I think the functions are
> > ther, but how combining?
> >
> > Perhaps someone knows a way?
> >
> > Thanks
> > MAnuel
> >
> > Richard Chirgwin schrieb:
> >
> > > grass-user-request at lists.osgeo.org wrote:
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> > >> Today's Topics:
> > >>
> > >>    1. highest and lowest point in catchment (Dr. Manuel Seeger)
> > >>    2. SHELL Variable problem: Workaround (Peter L?we)
> > >>    3. Re: SHELL variable not set (Martin Wegmann)
> > >>    4. Re: SHELL variable not set (Glynn Clements)
> > >>    5. Re: SHELL variable not set (Hamish)
> > >>    6. Re: SHELL variable not set (Markus Neteler)
> > >>    7. Re: Building wxgrass vdigit (Martin Landa)
> > >>    8. segment_format error with r.watershed (Wes Kent)
> > >>    9. union features of vector (Alfredo Alessandrini)
> > >>   10. Re: Snap across layers (Martin Landa)
> > >>
> > >>
> > >> ----------------------------------------------------------------------
> > >>
> > >> Message: 1
> > >> Date: Tue, 29 Jan 2008 10:01:20 +0100
> > >> From: "Dr. Manuel Seeger" <seeger at uni-trier.de>
> > >> Subject: [GRASS-user] highest and lowest point in catchment
> > >> To: GRASSLIST <grass-user at lists.osgeo.org>
> > >> Message-ID: <479EEB60.6050606 at uni-trier.de>
> > >> Content-Type: text/plain; charset=ISO-8859-15; format=flowed
> > >>
> > >> Hello all,
> > >> I hope the questions does not seem too simple, but I have now no real
> > >> good idea how to solve this simple problem:
> > >>
> > >> I need to find the highest and the lowest point within catchments
> > >> WITH their coordinates (and to get the information about altitude and
> > >> coordinates, of course)
> > >>
> > >> thanks for hints!
> > >>
> > >> manuel
> > >>
> > >>
> > > Manuel - hope I'm not being silly here, but I'd consider just using an
> > > SQL select directly to the data store.
> > >
> > > Select max( <altitude column> ), <latitude column>, <longitude
> > > column>, <any other column you want> from <table> where <boundary
> > > conditions of catchment>
> > > Select min( <altitude column> ), <latitude column>, <longitude column>
> > > <any other column you want> from <table> <boundary conditions of
> > > catchment>
> > >
> > > If you have to, you could extract only the catchment to a separate
> > > vector, so that you don't need to fool around with complex boundary
> > > conditions.
> > >
> > > But I'm sure that a genuine Grass expert will have a simpler solution
> > > than this ...
> > >
> > > Cheers,
> > > Richard
> > > _______________________________________________
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> > > grass-user at lists.osgeo.org
> > > http://lists.osgeo.org/mailman/listinfo/grass-user
> > >
> >
> >
> > --
> >
> > _______________________________________________________________________
> > Dr. Manuel Seeger
> > Wiss. Assistent                         Scientific Assistant
> > Physische Geographie                    Dpt. of Physical Geography
> > FB VI - Geographie/Geowissenschaften    Geography/Geosciences
> > Universität Trier                       University of Trier
> > D - 54286 Trier
> > Tel.:   +49-651-201 4557
> > Fax:    +49-651-201 3976
> > Web:    http://www-neu.uni-trier.de/index.php?id=9607
> >
> > _______________________________________________
> >
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> >
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-- 
Nikos Alexandris
.
Department of Remote Sensing & Landscape Information Systems
Faculty of Forestry & Environmental Sciences, Albert-Ludwigs-University Freiburg
.
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