Trying to convert lines to polygons

[Michel Wurtz - LTE]

Juan Bañuls wrote:
> *If I had all the lines labeled, could I get the
> polygon topology?. If so, how can I label the lines
> automatically?. What do I do after that?.

Labelling lines don't help for areas.  Polygon topology
is only based on line's geometry (all lines must be
connected).

> *I have one point inside of each area that exists in the
> map too (not in dxf but in shape). Could I use it to
> convert the lines?.

This is good for creating dig_att file.  If you have one point
in each area, v.support will label them.

> *I have generated some areas that were not detected with
> v.digit (labelling areas), but when I rerun v.support after
> using v.digit, they turn another time into lines. :-(

Lines are labelled either a either l.  If you have :


  +---------------------------+
  |\                          |
  |  \ line X                 |
  |   +                       |
  |                           |
  +---------------------------+

If line X is 'l' (line), it's OK, you may label the polygon
(here rectangular).  If line X is of type 'a' (area), v.digit
refuse to label it and v.support won't create a polygon.

When you clean the map with Grass, you have sometimes some
*very* small lines created by intersection of existing ones.

When a polygon can't be labelled, just zoom at each nodes.
You will probably notice one of these microscopic lines.
Delete them and labelling will work.

Another time where labelling seemed unpossible was with a
very large area. I digitized a line to cut it in two parts
and was able to label each part (with the same value, of
course).

> *Another thing: I have cleaned my DXF with AutoCAD MAP 2.0;
> if I import the new DXF and run v.support, I get ALL the
> areas. Is there any way to clean the map as AutoCAD MAP does?
> (it would be the solution).

Grass is not particulary efficient in cleaning (and the best
value to use for v.support is sometimes not easy to find).

-- 
Michel Wurtz    ENGEES - Laboratoire Territoires & Environnement
                1, quai Koch - BP 1039, F-67070 STRASBOURG cedex
                Tel: +33 03.88.24.82.45  Fax: +33 03.88.37.04.97