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 <[email protected]> *On Behalf Of *Bruce Mutton
*Sent:* Saturday, 7 December 2024 06:18
*To:* 'List for Therion users' <[email protected]>
*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
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