Tarquin
Was hoping you would offer!
Yes, this simple example makes a great starting point for an example that can 
shine light on extended elevation behaviour, and can be made progressively more 
complex to demonstrate behaviour changes.

I have in previous projects noticed all you mention in your point 1 below.
I don't have a problem with the characteristic you mention in point 2.  I think 
it is just semantics associated with the word 'ignore', and sequential process. 
 If you think 'break' then is it all OK?
Bruce

-----Original Message-----
From: Therion <therion-boun...@speleo.sk> On Behalf Of Tarquin Wilton-Jones via 
Therion
Sent: Monday, 11 November 2019 21:42
To: therion@speleo.sk
Cc: Tarquin Wilton-Jones <tarquin.wilton-jo...@ntlworld.com>
Subject: Re: [Therion] Breaking a loop at a specific station on extended 
elevation

Hi Bruce,

> Stepping through the process I take;


Thanks for that detailed explanation!

The main things that threw me were:

1. That Therion is stepping *backwards* along the oxbow - in the direction of 
the cave passage from the "start" instead of in the direction that it is 
surveyed. This means that you must use your "extend ignore" in that same 
direction. "extend ignore 6 5" works, "extend ignore 5 6" does not. Apparently 
I am not the only one who finds this surprising. Also, just to be confusing, 
"extend ignore 6" will cause it to go completely wrong and break both ends of 
the loop (sounds buggy to me), while if the loops had more stations, it would 
break at station *2* in the oxbow, rather than at station 6. In loops with more 
stations, you can also break the offending leg in both directions without harm, 
while in the data I gave you, you can't. So there are some real gotchas in here.

2. That you can then tell a leg that was ignored to not be ignored after all. 
It can have two states specified, one immediately after the other, and *both* 
are respected. The first makes Therion change its "main path"
of the extended elevation, and the second makes it draw the parts of the 
disconnected passage in the desired direction.

This would make an excellent mini topic on the wiki (in the existing article on 
"extend"). I have made a more complete version of the survey that allows it to 
show a couple more variations. So if you don't mind, I would like to use some 
of your words to turn it into a mini-topic.
Unless you argue, I will start to write this up.

Cheers again, and thanks for the wisdom.

Tarquin
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