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

Moritz Lennert mlennert at club.worldonline.be
Tue Oct 3 09:21:38 EDT 2006

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 :-)

Michel's changes date from 1998 and were apparently written for 4.2.1, 
so there was change since then. Don't know if that resolved the problem 
though... Nor which algorithm is better.


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