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

Moritz Lennert mlennert at club.worldonline.be
Wed Oct 4 04:50:12 EDT 2006

Maciej Sieczka wrote:
> Moritz Lennert wrote:

>> Maybe if you push hard enough someone will "just do it" - Dylan
>> mentioned it as a potentially "fun" project: 
>> http://grass.itc.it/pipermail/grassuser/2006-August/035529.html ;-)
>> and actually links to an implementation in c++, which actually looks
>> like more or less usable C to me).
> Sure it would be a good addition to Grass, but:
> 1. I need a tool to remove the vertices from a line based on a given
> threshold (understood as a distance from one vertex to another).
> According to v.clean manual it should be able to do it, but it's not.
> (I think I know how to workaround it by v.out.acii | awk | v.in.ascii.
> So I should be OK.)

To echo Hamish' question: Do you need to remove vertices from lines 
without changing the form of the line, or do you want to generalize the 
form of the line (in the way that is shown here: 
http://mpa.itc.it/markus/como2006/img9.html ?

> 2. This is a bug or a lacking documention, so either should be fixed,
> no matter what other pruning algorithm is added to Grass.

It actually also seems to be an ambiguity as to what pruning actually means:

- remove unnecessary nodes, or
- generalize


> 3. We can't remove any functionality in Grass 6, only add new.

We cannot change the interface of modules, but we can do what we want in 
terms of algorithms used behind this interface. Especially if the 
current algorithm is buggy.


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