[Therion] extend

Bruce Mutton bruce at tomo.co.nz
Fri Jun 8 22:49:23 CEST 2018

Marco, Evaristo

Looking also at Evaristo’s TopoDroid screenshots, which highlight the issue nicely, it seems to me that both TopoDroid (which I have not used) and PocketTopo (which I use) handle splays similarly, and automatically (maybe not TopoDroid?) and that automatically is the right way to do it, based on some combination of splay, leg and leg extend direction (difficult and arbitrary as a precise solution might be).  A precise solution is a difficult concept where extend switches say from left to right – although the software coders will be the experts on this.  At least PocketTopo mostly gives sensible splays.

Therion also messes up PocketTopo’s extended splay legs, and I just ignore it, because hopefully I still have the sketch to trace.

In theory a nice solution would be for Therion to somehow preserve what the source software gives it.  But in practice not so easy, especially as I always end up changing the extend specifications when it comes time to produce a finished drawing.


Marco, are you suggesting below that extend -1 would be left, extend 0 would be vertical, and extend 1 would be right?

Conceptually seems OK.  Personally I would not be bothered with that level of refinement, but I concede there are times when it would be nice to foreshorten a passage just a little in order to close a loop, or make something look or fit better.  Fairly often the extend direction I choose in the cave gets modified by the time I get to drawing the map!  More I think about it, the more I like it.


> btw, are vertical extend considered in the computation of the cave length by therion?

I don’t know for sure, but it would seem illogical for anything about the drawing or presentation projection (extend is a hybrid of both) to have any effect on the centreline length or depth reported by Therion.  Length and depth are a survey centreline property.  Length should be the sum of all survey legs that are not duplicate and not splay.  It also includes nosurvey legs. Depth is the vertical range between highest station and lowest station, and I think it goes further to include possibly the highest and lowest splay points and or up and down measurement. Conceptually an elevation drawing could affect the reported depth, but as far as I can tell, elevation drawings are not yet considered when producing 3d models, so it would seem unlikely that Therion would bring them into the depth calculation.  Or did I misunderstand your question?


Another idea.

Debug could have an extend option ‘debug extend’.  It might include adding arrow heads and L, R or V to the centreline of each survey leg (not so meaningful for splays). And maybe there is some way to graphically show why some ignore statements shift large chunks of centreline far to the left or right – maybe by showing hidden legs in very light colour?  In conjunction with ‘debug station-names’ this would help when trying to untangle large multi-looped survey networks.





From: Therion <therion-bounces at speleo.sk> On Behalf Of Marco Corvi via Therion
Sent: Friday, 8 June 2018 10:51 PM
To: therion at speleo.sk
Cc: Marco Corvi <marco.corvi at gmail.com>
Subject: [Therion] extend


i think that extend should take values in the interval [-1,1], ie also fractional values, plus some special value such as "ignore" to open loops, and "undefined" to let the program choose, because it's a nuisance to enter a decimal number for every shot (legs + splays).

therion uses the left/right normal/reverse etc. solution, 


and users should be allowed to set extend also for splays, if they need to.


for now, let's use left/right/vert, and ignore only to open loops


btw, are vertical extend considered in the computation of the cave length by therion ?



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