[Therion] Entering survey sketch without walls

[Bruce Mutton]

Bill

I’ve looked back through projects where I have made non-trivial and multi-scrap joins of scraps.

My early attempts, prior to my understanding distilled in https://therion.speleo.sk/wiki/drawingchecklist#wall  are characterised by brute strength manual joining of multiple points.  Painful.

More recent attempts strategically using line wall -visibility off and line wall -subtype invisible have almost always enabled semi-automatic joins (see https://therion.speleo.sk/wiki/tips#joining_scraps_together )

However, it seems not to be an exact science, and I have cases where a manual join should be required, but semi-automatic has sufficed.  Also cases where I have resorted to a manual join when I though semi-automatic should do it.  I’d be really pleased if someone can identify what the rest of the puzzle might be, or suggest improvement to those wiki pages.

 

What works best for a particular project will probably depend on whether it is structured such that scraps can easily span multiple surveys or not.  My projects are predisposed towards collections of scraps that can only reference one survey with ease.  That is probably why I join scraps in the middle of a void more often than some (by often I mean perhaps a dozen times in 60 -80 km and 15 years – usually when part of a large chamber is resurveyed some years later, or when a chamber is highly undulating and it is not possible to see walls, and is surveyed on multiple trips).  However don’t think differences in survey scrap relationship structures will change how join methods behave.

Rendering discontinuities should be expected where scrap joins are more complex than ‘straight between two open passage ends’.  If these bother you, then opting for some combination of the easiest, simplest, and ‘least morphing required’ will probably give the best result.

 

The attached sketch shows how I might arrange multiple scraps in a large void.  A simple 1 leg, 2 station survey with a minimal scrap as part of a much larger void and field of scraps.  Actual visible walls or pillars in a particular scrap should not be necessary, although I don’t think I’ve done one (with interior shading) without any visible wall at all.

 

Easiest option:

As much sketched cave as possible in one contiguous image in each th2 file.  Each scrap (and line and point) join is achieved fully automatically by snapping the points on top of each other.  The -visibility and -subtype properties of wall lines are likely to be less relevant to join behaviour, because the morphing induced by the co-incident points dominates.

Next option:

Non-contiguous sketches or sketches/scraps in different th2 files.  Semi-automatic joins required and sufficient here, in most cases.  Sometimes manual joins are required across wall -visibility off boundaries.

Last resort:

Add manual joins only at specific locations where the above fails, or where you want to joint non-wall objects, such as passage feature objects.

 

Bruce

 

From: Therion <therion-bounces at speleo.sk> On Behalf Of Bruce Mutton
Sent: Saturday, 7 December 2024 06:18
To: 'List for Therion users' <therion at speleo.sk>
Subject: [Therion] Entering survey sketch without walls

 

Bill

I've been misleading you (and everyone).  I should not multi-task quite so much.  I will try to rectify the situation tomorrow with a sketch.

 

In the meantime...

line wall -subtype invisible is what should be used for the open ends of scraps in your example, and should allow semiautomatic joins.

line wall -visibility off will preclude the possibility of semiautomatic joins, but does have a use case in large open voids that need to have a scrap join where there are no (real) walls at all.  Manual point joins will be required across those boundaries.  A sketch tomorrow…

 

Bruce

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