Footleg (and others)

Just some musings about how 'wall subtype invisible' and 'wall -visibility off' are intended to be used.  It seems Footleg is wanting a wall linetype that does not exist, and so quite sensibly making his wall invisible in some way (so therion knows where the passage interior is), and then overlying his wall with the line type he wants (ceiling step, chimney, whatever). Clever.

Aside from the loch issues my experiences with pdf and kml outputs suggest that unless you do this right there will be problems in some cases.

This is how I think therion might be intended to behave, these are my guesses, so please comment if I am wrong.

wall:invisible (or ‘wall subtype invisible’ is exactly equivalent)

means 'wall does not exist'.  Ie Use this syntax to show that this is the boundary of the interior of the passage for this scrap but it is NOT a wall.  Eg A passage branches off here and there is an open end (wall:invisible required if the open end is wider than the passage/scrap width) or there is a junction at the end of the scrap where three or more passages join, and you need to help therion understand that the ‘blank polygon’ inside the junction is in fact inside the passage, and you don’t want to (or cannot) use the solution here  http://therion.speleo.sk/wiki/doku.php?id=tbe:wiki3&s[]=join#joining_scraps to fill in the blank.

Therions scrap ‘join’ statement (default usage) ignores walls with subtype invisible (as if they don’t exist) and so this is where Footlegs workaround for unsupported wall linetypes could come unstuck.  Some really odd joins could manifest, requiring the user to adopt the more tedious explicitly defined line by line joins.

Therefore if you have a case where there really is a wall, but you want a work-around to get a different linetype, then wall – visibility off is probably what you should be using.

Is this an OK explanation?

Bruce