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?
Now, I’m trying to interpolate a suface with IDW (very slow…)
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?
Sounds like a good approach.
Now, I'm trying to interpolate a suface with IDW (very slow...)
You should use layer=0 if you want to read the elevation co-ordinates as the 3rd dimension of the vector data. The way you have written it is reading these from a database field which will slow it down a bit - you don't need a database connection as you are storing the elevation data as part of the vector map itself.
Another question: what is the precision of this surface? What contour
interval can I generate?
The elevation raster map will be generated according to the extents and resolution of your current region. g.region -p will show this. If your region is too big (i.e. extends beyond the region covered by the points) or the resolution is too high that could be another reason why it runs slowly. In general v.surf.idw should be quite fast.
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:
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.