[Therion] Adding entrance breaks extended elevation

[Bruce Mutton]

Hi all

We've been surveying a cave from half way between two entrances, and working
outwards towards those entrances over a number of survey trips.  As each
survey trip has been completed, I have been drawing, and constructing an
extended centreline, and attaching scraps.  The extended centreline is just
a little bit complicated, with two loops, but I have managed to get the
breaks where I want them, and offset passages to lay it out nicely.  As each
centreline is added, I modify the extend left and right for that survey to
suit the extended centreline shape that I want.  I have 'anchored' the
downstream entrance with a dummy survey leg, until I surveyed downstream to
that entrance and I could remove the dummy leg.  I have 'extended right' to
the downstream entrance.

All has gone well until I surveyed out of the upstream entrance, extending
left, mostly.  But as soon as I add a station flag to the upstream entrance,
the shape of the extended centreline is broken.  It looks like Therion is
overriding the 'extend start' that I have in the middle of the cave, and
replacing it with a start at the top entrance.  This completely scrambles
the shape of the centreline and attached scrap drawings. It looks a bit like
the default behaviour listed here
<https://survex.com/docs/manual/extend.htm>  (the first paragraph of the
main text) for Survex.

I have tried a few approaches to avoid this undesirable behaviour, but
nothing yet has worked.  

I would rather not try to recreate the extend development from upstream, as
Therion seems to want me to do, because even with such a simple cave, there
is some complexity and time involved in figuring it out.

 

Good, but no upstream entrance flag



 

Bad, after adding upstream entrance flag the extends are broken

   station 4.24 "Top Entrance" entrance



Any suggestions?

 

Bruce

 

 

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