[GRASSLIST:2721] Re: How to get topology of area edges

[Radim Blazek]

On Monday 23 February 2004 22:10, Robert Stein wrote:
> Hello,
>
>     I'm attempting to read GRASS's ascii vector output into a graphics
> display program that I'm writing...  I produce this output (with
> v.out.ascii) from a valid GRASS vector layer containing area polygons. What
> appears in the resulting data file is a line that denote an area and a
> number of points followed by these points... i.e.
>
> A 4
> easting northing
> ...
> easting northing
> ...
>
> However... it appears that each area is not a closed ring as is stated in
> some of the documentation... but instead it appears to be an area-edge
> representation which is stated in some other documentation :) This is great
> with me... and makes a good bit of sense... but I can't seem to find the
> information that associates a particular edge with a polygon (i.e.
> topology)
>
> Can someone point me in the right direction here? Is there some implicit
> relationship that I'm missing or don't understand... Thanks in advance for
> your help

Try v.out.ogr format=GML (5.7). You get closed polygons and it sounds
much better if your application is based on GML :)
Or better use OGR directly (with GML for example). There will be GRASS support 
in OGR in future so it will be possible to switch to direct access.

Radim