[Therion] Handling of tape and backtape in survey data

[Stacho Mudrak]

Thanks Bill for pointing that out. BACKTAPE/BACKLENGTH reading support was
added to therion in the latest commit.

S.

On Thu, 30 Dec 2021 at 09:44, Bruce Mutton <bruce at tomo.co.nz> wrote:

> > instead Toporobot just generates a new station for the backsite.
>
> PocketTopo automatically detects backsights if they are taken immediately
> after a foresight.  So the software handles the station naming, no user
> intervention required.  While I processed the only survey I ever did this
> way with Therion, it never made it into the main cave dataset and so I
> didn't get as far as checking the survey length was correct (or doubled).
> I'm pretty sure it would be correct though.  It was only done to find a
> reasonably precise gap in an 'almost looped' passage.  The gap was too big
> to dig so we lost interest and I haven't drawn the enhanced accuracy map
> yet.  It is at the bottom of my priority list.
> The exercise was also helpful to gauge the frequency and size of
> foresight/backsight mismatch with 'three-shot' disto readings.  My
> conclusion: a few instances that may be of interest occur, but not enough
> to ever bother actually taking all those backsights.  Have never done a
> backsight since.
> Our disto driven loop closures are typically 0.5% (I like to think) but a
> bad one will be 1.0%.  Compared to our pre-disto loops over a decade ago
> which were typically 2% and a good one 1%.  Although I prefer to think in
> Survex's standard deviation approach to loop closure, which tells a
> different story about which loop is good and which not...
> Bruce
>
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