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

[Moritz Lennert]

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?

I think Markus responded to my remark on lack of documentation.

> 
> Moritz just supposes but he is not sure. And if you look into my
> original email you'll that he's wrong:
> 
> 1. a *straight* line, consisted of 4 vertices, at regular intervals of
>    10
> 2. thresh>0.03 prunes all vertices (besides the nodes of course)
> 3. thresh<=0.03 prunes none
> 
> Then Moritz's idea is wrong.
> 
> 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.

Check

http://freegis.org/cgi-bin/viewcvs.cgi/grass6/lib/vector/diglib/prune.c?rev=HEAD&content-type=text/vnd.viewcvs-markup

There is an explanation of the algorithm at the beginning.

Moritz