Adding entrance breaks extended elevation
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
Well, I have solved my problem with this extended centreline, but not the mystery of Therion! My extended centreline relied on a lot of auto generation, and for some reason adding the entrance flag broke some of the auto generation far away in the middle of the network. After a reasonable amount of explicitly extending every leg, everything suddenly popped back into place. There remain other auto generated sequences in the dataset, so maybe future unpleasant surprises await me. As myself and others have pointed out, extended elevations can be fickle. I have added todays insights to the wiki <https://therion.speleo.sk/wiki/extend#summary_of_all_extend_options_for_sur vey_centrelines> . It would be nice to have some debug functionality aimed at communicating to the user exactly how Therion has created the extended centreline. Maybe something graphical in the pdf, and an optional text listing in therion.log of every extend function in the order it is executed. ie Start 4.1 Left 4.1 4.2 Left 4.2 4.3 vertical 4.2 4.4 right 4.4 4.5 etc Bruce From: Therion <therion-bounces@speleo.sk> On Behalf Of Bruce Mutton via Therion Sent: Friday, 20 July 2018 22:58 To: 'List for Therion users' <therion@speleo.sk> Cc: Bruce Mutton <bruce@tomo.co.nz> Subject: [Therion] Adding entrance breaks extended elevation We've been surveying a cave from half way between two entrances, and working outwards towards those entrances over a number of survey trips. .. 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. .. 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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Bruce Mutton