[GRASS-dev] Re: [GRASS-user] v.clean tool=prune - 'thresh' interpreted wrong?

[Hamish]

Markus Neteler wrote:
> On Tue, Oct 03, 2006 at 02:56:18PM +0200, Maciej Sieczka wrote:
> > Markus Neteler wrote:
> > > On Tue, Oct 03, 2006 at 02:23:56PM +0200, Moritz Lennert wrote:
> > 
> > >> I would guess that the prune tool prunes all 
> > >> "unneccessary" nodes on a straight line, i.e. any node which is
> > >not  > necessary to define the line, and this whatever the
> > >threshold. >
> > >> The threshold only applies in cases of change of direction (i.e.
> > >angles). >
> > >> Just another example of the need for much more documentation for 
> > >> v.clean, including example diagrams like the one for the rmsa
> > >tool.
> > 
> > > Fully agreed...
> > 
> > Markus,
> > 
> > Agreed regarding what?
> 
> ... regarding that more documentation is needed.
>  
> ...
> > And I need to know exactly how the thresh in prune works, as I'm
> > using it for my work. The result will be a script that I'm going to
> > publish. Please - if anybody knows, tell me. I'd love to update the
> > manual accordingly.
> 
> Apparently it can be only reverse engineered (luckily it's FOSS).
> I was not too happy with my attempts to use the prune algorithm,
> I don't think that it works reasonable well.
> 
> But this is an old story:
> http://grass.itc.it/pipermail/grassuser/1995-January/012655.html
> http://grass.itc.it/pipermail/grassuser/2006-July/035373.html
> http://grass.itc.it/pipermail/grassuser/2006-August/035529.html
> 
> The first mail indicates that the problem is known and wasn't
> resolved so far. Time to switch to another algorithm :-)


so the existing tool acts like:
 v.clean tool=simplify_without_geographic_change"
? (removes redundant verticies in a line (angle==0))

and the Douglas-Peucker method could be called tool=generalize  ?

??

to me the meaning of "prune" is ambiguous.

v.clean --help:
  prune: remove vertices in threshold from lines and boundaries, boundary
is pruned only if topology is not damaged (new intersection, changed
attachement of centroid), first and last segment of the boundary is
never changed


this sounds like it is meant do "generalize".

???

need to do some tests & create screen shots (eg v.voronoi help page)
to be sure.


Hamish