Digitizing in GRASS

[David D Gray]

Alejandro Imass wrote:
> 
> David D Gray wrote:
> 
> >
> > Hi Alejandro
> >
> > v.trim does this - as long as you set the threshold option to 0, then
> > it won't make any other changes. But you must copy the dig_att file from
> > the old map to the new, as v.trim doesn't (it seems) copy attributes.
> > It just builds an empty attribute file. Then once you've copied it,
> > run v.support. Voila - all excess nodes are gone!
> >
> > There's also a recent module called v.build.polylines which also
> > is supposed to do this but I haven't been able to check it yet.
> > But there's no manual way of elliminating just one node while
> > in v.digit.
> >
> 
> I thought there was some secret keys (like line un-break) because I have
> noticed some keys I press accidentally which are not in the menus do some
> things, but I haven't looked closely to see what they do.

You may well be right, but I don't know if there are any.

> 
> 
> Do you have any clue as to what could be happening in my second mail.
> 
> Sorry that my character sketch got all messed up. It's just two big polygons
> sharing a middle line, and the middle line is cut by a smaller polygon.
> 

Actually, I was unable to verify this, as I tried a map with the
topology you described, and it behaved just as expected. The
listings produced by the export modules are arcs not rings. The six
listings produced therefore form only part of a polygon each, the
so-called `arc-node' format, unless it is a simple island, of
course, but there is none in this topology. If v.out.ascii or
v.out.arc is producing actual closed rings there must be
something wrong with the original map.

David