[GRASS-user] Surface

[José María Michia]

> I need to create countour... so, I think, I must interpolate a surface from
> this points making something like a DEM, and after, interpolate the
> contours... Is this correct?

Yes.

In addition to IDW, you can use RST for interpolate points and
generate a raster surface.

First all, set appropiate region and resolution to something
reasonably. For example:

g.region -p -a vect=pontos res=100

Adjust res to fit your needs.

Interpolation can be made with:

v.surf.rst input=pontos scolumn=Elevation elev=dem --overwrite

And generate the contours with:

r.contour input=dem output=contour  step=2.5

> Now, I'm trying to interpolate a suface with IDW (very slow...)
>
> v.surf.idw input=pontos2 en PERMANENT output=teste npoints=12 layer=1
> column=elevation --overwrite
>
> Another question: what is the precision of this surface? What contour
> interval can I generate?

The accuracy of these models depends mainly on the accuracy of the
original data.
	
The resolution of the grid and step (the contour of separation) also
depend on issues of representation, such as the scale. Contour step
(vertical separation) also depends on topography. For example, in
plane surfaces, step must be small.

I hope this will be helpful.
Saludos
Jose

> Regards,
>
> Raphael Saldanha
> BRAZIL
>
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