> using a border line instead of an invisible wall for scrap borders in centre > of a passage / open space
There are a number of considerations here. This wiki post describes them https://therion.speleo.sk/wiki/drawingchecklist#wall It may be that using line wall -visibility off is a better solution than either line wall -subtype invisible or line border -outline out -visibility off Tarquin’s overall approach is how I would do it. Always end/start surveys between pillars, and each open end of a scrap only joins with one other scrap, to avoid the open triangle in the apparent interior of the cave. Even if you make a mistake in the field and end a survey in the middle of a void far from the pillars, strategic drawing of the scrap walls can mitigate the problem. Imagine Tarquin’s sketch attachment with say the left-hand survey station missing, so the station joining with another survey to the left is in the centre of the void. So you draw the sketch exactly as Tarquin has (with walls defining the pillars at distant-left, just there is no station between them) and it will work. See also https://therion.speleo.sk/wiki/faq#how_do_i_join_three_scraps_in_a_y-shape. The XTherion ‘tricky’ image demonstrates a simple case. What is really happening is that a three-scrap join is turned into a series of two-scrap joins. These can then be joined semi-automatically as described in https://therion.speleo.sk/wiki/tips#joining_scraps_together Bruce
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