lines and areas

[David D Gray]

Malcolm Williamson wrote:
> 
> Stefan,
> In v.digit, you can re-type lines to area edges. You can also do this in
> bulk by converting to ASCII, using an editor to change all leading "L"s
> to "A"s, and re-importing with v.in.ascii. Either way, you'll have to
> manually attribute all of the areas in v.digit. Also, I'm really not
> sure how robust the GRASS topological model is, especially concerning
> multiple levels of nested areas ("islands").

Hi,

Actually there is not really an issue with multiple nesting, because
really there is no nesting. Here as in other formats, such as shapefile,
each area entity consists of a single ring giving the outer perimeter
and a series of indices linking to `primary islands'. I have built slope
maps which are polygons with often deeply nested levels that have built
correctly wihtout problem. For some time there were many modules that
didn't handle areas correctly, but more recently (hopefully) these have
been updated.

David

> 
> Best regards,
>         -Malcolm Williamson
>          CAST - University of Arkansas
> 
> > Stefan.Neumann at agrar.uni-giessen.de wrote:
> >
> > Hi Grass,
> >
> > is there a way to convert lines to areas ? I create lots of
> > contour-lines with r.contour and I would like to make statistics
> > (r.report type=area) on the areas surrounded by the contour-lines.
> > This doesn't work though, because r.contour only creates lines, not
> > areas.
> >
> > Also I would like to create a map where the areas are filled with a
> > color according to their attribute (with v.to.rast). This also only
> > seems to work with areas.
> >
> > TIA, Stefan