[GRASSLIST:793] Re: Fwd: slope map,watershed

[Massimiliano Cannata]

I'm not sure to have understand all, but:

1- a raster map is a "box" rappresentation, in fact in a raster
ascii you have an header that says the coordinate extention of your
"box" (or better to say region). So you cannot have any border on
it.

2- when you intepolate you will always have some border problem,
that's because on your border (note, the border of your
interpolated set of line or point) you have only one side value,
while on the other you have null value so you begin to invent....
it's usually done to keep a larger area and then take off a buffer.

3- if you want to have a raster with your value only inside the
watershed consider to interpolate, calculate slope and after assign
a null value outside you interest region. I f you can create a
raster that works as a mask (for example with value=1 inside your
watershed and value=0 outside) you can easly do it with r.mapcalc.


Ramin Safa wrote:

> Hi
> Regarding folowing email
> My area is a watershed but:
> I don want to do r.watershed
> I need to use only my area(watershed ) not a squer(whole
> screen)and i need slope,,...
> please if anybody knows ,help me
> sincerely
> Ramin
>
> Note: forwarded message attached.
>
> =====
>
> Ramin Safamanesh
> Department of  Environment Science , UPM
> Email :  rsafamanesh at hotmail.com Tel  :  0060122399448
>
> __________________________________
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>   --------------------------------------------------
>
> Subject: [GRASSLIST:781] slope map
> Date: Mon, 21 Jul 2003 18:53:15 -0700 (PDT)
> From: Ramin Safa <raminsafa at yahoo.com>
> To: mlennert at club.worldonline.be, grasslist at baylor.edu
>
> hi
> *Regarding slope map(raster),befor v.to.rast my map had a
>   border but after v.to.rast  ..the border is disapeared
> and **because of this when i run : r.slop.aspect ....slope
> map
>    and aspect map and .. will be wrong, am i right or no?
> ***if this is true how i save the border and if it is not
>
>    true how i solve my problem?
> ****and also if i run v.surf.rst or r.surf contour i have
>    same problem :out of the borderplace(but dont have
>    border) the colors is confused.
> actually i think ,in vector map the border is a continuse
>    of end of contours line(related to digitizing)..
> Regards
> Ramin
> ---
>  Moritz Lennert <mlennert at club.worldonline.be> wrote:
> > Ramin Safa said:
> > > hi Moritz
> > > thanks ,i did v.transfom.
> >
> > And did it work correctly ? Have you checked with
> > d.what.vect to see the
> > resulting attribute values ?
> >
> > > but now please go to problem
> > no:737<grasslist>r.slop.aspect
> >
> > I've seen your mail, but can't answer your question
> > without more
> > information about your data. On what file did you run
> > r.slope.aspect ?
> >
> > > the answers is not real and not correct.
> >
> > Then probably the data is not correct.
> >
> > > r. report also is no correct.
> >
> > idem
> >
> > > i dont know why.
> >
> > One reason might be that your contours were actually
> > digitized as areas,
> > not as lines. You might want to try by transforming all
> > the areas to lines
> > (you could use v.area2line). After the transformation you
> > would have to go
> > into v.digit and lable the lines, but seen that you don't
> > have too many of
> > them, this shouldn't be too much work. Then you could use
> > v.surf.rst or
> > something like that.
> >
> > Moritz
>
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--
-------------
Ing.  Massimiliano Cannata
Istituto di Scienze della Terra - SUPSI
C.P. 72 - CH-6952 Canobbio (Ticino, Switzerland)
Tel +41 91 /935 12 25 - Fax +41 91 /935 12 09
eMail: massimiliano.cannata at ist.supsi.ch
Internet: http://www.ist.supsi.ch