Digitizing in GRASS Part II

Hello to All.

We found that trim does the job asked for in the previous mail, but the
question still remains: is there a manual way to do it in the digitizer?

Now I have a bigger problem:

If I digitize 3 polygons , one which is contained in the other two
(intersects the bigger ones), I am obligated to have at least 4 nodes,
where
the polylines join (X mark the nodes):

***************************************
*
*
*
*
* POLYGON 1
*
* ****************** *
*
* * *
X**************X POLYGON 3 X*****X
*
* * *
* ****************** *
*
*
* POLYGON
2 *
*
*
*****************************************

When I export the above file into GRASS native ASCII format or to
ARC/INFO ASCII format I get 6 polygons because the system closes the
polylines at the nodes (it adds new lines between the nodes cutting the
whole thing in may other polygons.

If the areas are being labeled correctly and they are only three, how
come the system has to close these polygons again when exporting.

Any clues?

Thank You,
Alejandro Imass

Alejandro Imass wrote:
[...]

If I digitize 3 polygons , one which is contained in the other two
(intersects the bigger ones), I am obligated to have at least 4 nodes,

[...]

When I export the above file into GRASS native ASCII format or to
ARC/INFO ASCII format I get 6 polygons because the system closes the
polylines at the nodes (it adds new lines between the nodes cutting the
whole thing in may other polygons.

You get 6 lines, which is true in your drawing : v.out.ascii or
v.out.arc doesn't export polys, only lines...
If you want polygons, you have to use the arc/info buid command
on your lines (in $LOCATION/dig_att, you will have a file of the
same name as your line file that contains the points needed by
Arc/info (and Grass) to build polygons.

If you import your file, you will see that the lines are OK, but
it's only line (white in v.digit) not area limits (blue in v.digit)

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

Michel Wurtz - ENGEES/CEREG wrote:

If you import your file, you will see that the lines are OK, but
it's only line (white in v.digit) not area limits (blue in v.digit)

OOOps! it's area limits (those are white) and the topology still exists
because the dig_att file is copied again (both ascii and binary vector
files share the same dig_att directory)

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