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

Maciej Sieczka tutey at o2.pl
Wed Oct 4 05:53:59 EDT 2006

Moritz Lennert wrote:

> Maciej Sieczka wrote:

>> Moritz Lennert wrote:

>>> 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 ?
>> The latter. I want to remove all the vertices that are distant from the
>> line starting node not more than the give thresh. A line:
>> x--o1-o2-->----o3--x
>> "x" - node
>> "o" - vertex
>> ">" - line direction
>> "-" - 1 length unit
>> thresh=3 would remove o1, thresh=5 the o1 and o2 and so on

> This sounds like something still different, as you make it dependent on
> the starting node.

Still we don't know how the thresh works for pruning.

> I don't think that the prune tool was ever thought to work this way.

You don't know how it works. Then how do you know how it doesn't work :) ?

Getting back to my original post.

The line:

$ echo "L 4 1
	 10 10
	 20 10
	 30 10
	 40 10
	 1     1" | v.in.ascii -n out=line format=standard

Imagine it as:


"x" - node
"o" - vertex
"-" - 5 length units

$ v.clean input=line output=line_pruned type=line tool=prune thresh=0.04

removes o1,o2. Anything bigger does the same. Anything smaller doensn't
remove any.

Why? Should it be like that or not?


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