[GRASS-user] v.generalize: strange behaviour on win?

[Markus Metz]

On Sun, Jan 29, 2012 at 1:12 PM, Paolo Cavallini <cavallini at faunalia.it> wrote:
> Il 28/01/2012 11:58, Markus Metz ha scritto:
>
>> are left have mixed up attributes. That was fixed such that boundaries
>> are not generalized if the generalization would damage topology. For
>
>
> OK, now I see. I think adding a warning in these case should be useful. Is this
> documented in the man?

These cases are reported in verbose mode. This is not mentioned in the
manual. BTW, v.generalize in 6.4.2 and above behaves like v.clean
tool=prune since version 5.x, but offers far more methods. The
topology checks and skipping some boundaries if it is not possible to
safely generalize them is in this sense not new, but has been there
for many years.

> However, in my case topology is maintained, even if the areas are obviously overly
> simplistic.

My previous description was obviously incomplete. Output topology is
always correct, independent of the version. In 6.4.1, topologically
incorrect boundaries are deleted at the end of the module. In 6.4.2
and above, generalized boundaries are tested if they would damage
topology, if no, fine, if yes, the original is kept. Because in 6.4.1
the original boundaries are not kept and all incorrect generalized
boundaries are deleted, the output may suffer from heavy losses, i.e.
areas disappear (see nc example mentioned earlier and also your own
example).

Markus M

On the other hand, I confirm that the attributes are mixed up.
> Thanks a lot for the explanation.
> All the best.
> --
> Paolo Cavallini - Faunalia
> www.faunalia.eu
> Full contact details at www.faunalia.eu/pc