[Therion] Entering survey sketch without walls

[Bill Gee]

Hi Bruce and everyone -

I added two more scraps to my Practice Mine map.  These scraps are 
completely interior - no walls, just columns.  Using automatic join 
works quite well.  There is one very small sliver between two of the 
scraps which might be related to inaccurate survey data.

I had "line wall -visibility off" for the edges of every scrap.  I took 
those lines out where two scraps meet - except for one which leaves a 
big white triangle.  Odd.  The "-visibility off" lines are still present 
around the edges of the scraps.  I had to use one line join to get the 
actual wall to connect smoothly.

When the time comes to do this for real, I can put those lines in as 
each scrap is drawn.  Taking out the lines is easy.  I might also use 
line joins for the columns that sit on scrap boundaries.

The updated project files are at

https://campercaver.net/MiscFiles/PracticeMine.zip.

Compare PracticeMine-6.pdf and PracticeMine.pdf.  The -6 file has all 
"-visibility off" lines present and uses a semi-automatic join between 
two scraps.  The other two scraps are an automatic join.  The file with 
no number takes out most of the hidden lines and uses all automatic 
joins except for the outer wall.

It is worth noting that the centerline data is not very accurate.  I 
drew the sketch on graph paper (scans are in the ZIP file) then used my 
cave protractor to measure the length and angle of each shot.  It is 
probably not accurate to more than 3 degrees and 2 feet.  A real in-cave 
survey with real numbers from a Disto will probably produce better joins.

All of your advice and this practice map has taught me a lot.  When the 
time comes to do the real map I have a good idea how to proceed.

Thanks!

===============
Bill Gee

On 12/7/24 20:19, Bruce Mutton wrote:
> 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 <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 
> <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 - 
> visibilityand -subtypeproperties 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 offboundaries.
> 
> *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 offwill preclude the possibility of 
> semiautomaticjoins, 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
> 
> 
> _______________________________________________
> Therion mailing list
> Therion at speleo.sk
> https://mailman.speleo.sk/listinfo/therion