[GRASSLIST:1831] Re: Creating a DEM

[Markus Neteler]

On Fri, May 11, 2001 at 12:24:08PM +0200, Andrea Aime wrote:
> Hi everybody,
> some time ago I was told that DEM generated from contour lines 
> suffer some problems and that it's better to start from sites...
> anyone can confirm/reject this? In general, what's the best starting
> point to generate a DEM? Are r.surf.contour and v.surf.rst equivalent?
> Regards
> Andrea Aime

Hi Andrea,

(I cc to the list)

no, the r.surf.contour and v.surf.rst differ. While r.surf.contour is using
an flood fill algorithm for linear interpolation and v.surf.rst is using
regularized splines with tension.

I have added this to the r.surf.contour html page right now (found the
explanation in the old mailing list archive).

Hope this helps,

 Markus


> Markus Neteler wrote:
> > 
> > On Fri, May 11, 2001 at 10:33:14AM +0200, michele.rocc at libero.it wrote:
> > > Hi,
> > >
> > > I'm trying to create a DEM from a "scannerized" map, because of the
> > > large amount of feature I thought to extract in some way the contour
> > > lines using r.thin and r.line, then I heard that maybe there is som
> > > problems in doing that
> > 
> > Hi,
> > 
> > maybe my last mail on r.line was confusing. In fact it does what's expected
> > (generates vector lines from raster lines even with diagonal lines. Hi Aldo
> > Clercini, maybe it's what you have been looking for).
> > 
> > > (something like r.surf.contour doesn't work fine  yet..).
> > It does, however it is still limited to CELL maps (no floating point dem's).
> > You can use it with fp maps as well, but will loose the precision.
> > 
> > > Well, is my idea possible to do? I know that any line will be
> > > reproduced but I wanted to eliminate manually by v.digit the "not-
> > > contour" lines.
> > > Anyway, even it I decide to copy all contour lines point by point, is
> > > there a working feature in GRASS to create the DEM?
> > 
> > You may use the v.surf.rst which runs very well and produces smooth DEMs.
> > 
> > Regards
> > 
> >  Markus

-- 
Markus Neteler *  University of Hannover
Institute of Physical Geography and Landscape Ecology
Schneiderberg 50 * D-30167 Hannover * Germany
Tel: ++49-(0)511-762-4494  Fax: -3984