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
