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!

Best

Stu



> On Jul 23, 2017, at 5:47 AM, Moritz Lennert <[email protected]> 
> wrote:
> 
> On 22/07/17 23:58, Jeshua Lacock wrote:
>>> On Jul 22, 2017, at 4:47 AM, Moritz Lennert <[email protected] 
>>> <mailto:[email protected]>> 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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