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

Jeshua Lacock jeshua at 3DTOPO.com
Mon Jul 24 01:04:23 PDT 2017

> On Jul 23, 2017, at 7:14 AM, Stuart Edwards <sedwards2 at cinci.rr.com> wrote:
> 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.

Hi Stu,

Some lines start and end positions can vary a great deal. As shown in the first image; in the upper left corner the orange line goes well past where the purple line ends.

> 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?

Is there a way in grass to select lines based on distances, or are you speaking of a possibly custom solution?

> 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.

I tried segmenting the lines at various lengths and I actually get worse results since in some places where they overlap they are removed, but the segments that don’t overlap aren’t removed.

> 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!

Hey that’s awesome! Thank you and glad to hear you are still at it! Your name actually looks familiar too.


Jeshua Lacock

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