[Therion] Splays - Revisiting Breaking extended elevations

[Stacho Mudrak]

I have tried to fix all the extended elevation issues in the latest
development snapshot (commit 6860f82
<https://github.com/therion/therion/commit/6860f82e616edb5e0fc7b35120cfc68eb682897a>
).

1. splay shots should be extended relatively to survey shot with closest
(horizontal) bearing

2. there is a possibility to specify reduction ratio for extended elevation
(0 = vertical, 100 = normal left/right) - just use "extend <number>"

3. extend ignore via path of 3 points should now work -- use "extend ignore
<s1> <s2> <s3>". I think this should allow all crazy loop configurations to
be solved, but I am not still 100% sure.

Unfortunately (but not surprisingly :/), there was a bug with the extended
elevation algorithm. In the case there were loops present in the
centerline, it caused some random behaviour.

I have tried to fix this bug, but it required quite a deep change to the
code. My data seems to work, but I suppose, there may be some cases when it
still can fail. Could you please try your datasets?

Thanks, S.


On Thu, 30 Jul 2020 at 01:18, Olly Betts <olly at survex.com> wrote:

> On Wed, Jul 29, 2020 at 06:25:50PM +0100, Tarquin Wilton-Jones via Therion
> wrote:
> > TopoDroid, Pocket Topo and Survex all extend only the legs. They all
> > keep the splays in the "same" direction (relative to the leg) as they
> > were before, which makes them normally perfect for drawing extended
> > elevations. They can project forwards and backwards out of the page (so
> > to speak), so they end up the right distance, visually, from the station.
> >
> > There is always the issue when you are at a station where the extend
> > direction changes from left to right or vertical, since at that point
> > you don't know whether a splay should take its direction from the leg
> > before or the leg after (or the "nearest" leg to it - perhaps the most
> > useful answer). Survex gets this wrong sometimes, but is normally useful.
>
> Examples of where Survex it gets it wrong are definitely of interest.
>
> I added extending of splays just over 3 years ago, and the NEWS entry
> (which also explains the algorithm used) explicitly invites feedback:
>
> | + Splays are now carried over the extended survey.  The current
> |   handling is simplistic, but should do a good enough job to be more
> |   useful than discarding splays.  The splays at each station are all
> |   rotated together based on the bearing between the stations either
> |   side of the current one along the first path extended through that
> |   station.  This nicely handles dead ends and the situation at the top
> |   or bottom of a pitch, and should tend to pick an angle close to the
> |   passage orientation along a traverse.  It's weakest at junctions.
> |   Feedback (especially examples which could be handled better) most
> |   welcome.
>
> But so far the only thing I could possibly count as feedback on this
> subject is what you wrote above (which is good to hear overall, but it'd
> be helpful to have some details of where you've seen it go wrong).
>
> Cheers,
>     Olly
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