[Therion] Setting -outline for pit lines

[Bruce Mutton]

>Maybe there is a possibility that I can construct a cave where the proximity of openings/entrances and passage curves will cause it to construct the passage on the wrong side of a line. And in such a case, the solution would be to make invisible walls. Interesting. I will probably randomly bump into that, one day.

Scraps with open ends that are wider than they are long is a good start if you want to make things tricky.  And yes, invisible walls (or -visibility off) is the solution.  Details here https://therion.speleo.sk/wiki/drawingchecklist?s[]=scrap#wall 

Bruce