[GRASS-user] Recommended v.select relate matrix?

Stuart Edwards sedwards2 at cinci.rr.com
Sun Jul 23 06:14:35 PDT 2017

Hi - 

Not a trivial problem -  Seems to me that there may be multiple steps depending on the precision required.  

First, if a line starts and ends at the same place as the target line does that qualify? - it would appear to serve as a good initial screen.  If that's too rigorous, maybe add a tolerance of +/- 10 or 100m or whatever is appropriate for the expected precision.

If there are several lines that meet this first test perhaps calculating the distance between each of them and the target (node by node) and selecting the one that results in the minimum cumulative distance?

If the lines are not fully coincidental (i.e. don't start and end at roughly the same points), some segmentation would be required so that these tests could be applied.

BTW - If it wasn't for you I doubt I would have ever have become a GRASS user.  I used your CDs with the original pre-compiled Mac binaries for a long time in the early 2000s.  Thanks for that.  It's been a great ride!



> On Jul 23, 2017, at 5:47 AM, Moritz Lennert <mlennert at club.worldonline.be> wrote:
> On 22/07/17 23:58, Jeshua Lacock wrote:
>>> On Jul 22, 2017, at 4:47 AM, Moritz Lennert <mlennert at club.worldonline.be <mailto:mlennert at club.worldonline.be>> wrote:
>>> Actually I think that showing us the example with all lines will make it easier to think about solutions.
>> Hi Moritz,
>> The purple line can select lines that just cross it like the red line shown in the attached image.
> But you said 'crosses' is not sufficient. Could you explain why ? Again, without a view of the lines you do not want to select, I'm not sure I understand the issue.
>>> A small buffer around the selecting lines might help ?
>> Thanks for the suggestion. Perhaps I am doing things wrong, but adding a buffer makes things worse, since the buffer can overlap other unrelated lines that the original line doesn't.
> See above...
> Moritz
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