Tarquin, I had confused the meaning of "extended" and "elevation"
scraps. What I really want is "elevation" where there is no projection
on a specific bearing.
OK, this is only slightly different. Much of the process is the same
though. If you have a very simple cave, and you have already drawn a
perfect extended elevation while you were in the cave, great, you can
skip a bunch of steps. However, I find that in the cave, I have no idea
how the extended elevation will end up being drawn, so I don't have
anything useful, and need to redraw it all when I get out.
Firstly, you need to decide whether you start on the left or right of
the survey. You probably decided this while you were in the cave (or
maybe not), but you will need to re-decide now that you have enough cave
data to work out where nasty overlaps happen, and what direction makes
most sense. You add the "extend start" and "extend left" or "right"
commands for your survey.
Then decide where to fold left and right to make the cave most
understandable - this is an art form. Decide if some passages need to be
shortened or lengthened. Add the commands to change the extend direction
as needed, or to scale legs as needed. Keep exporting it as a PDF so you
can see how your design looks. It really helps to do this before you
have drawn scraps. If you have already drawn scraps ... well ... I have
a map like this:
map skeletonMEE
thecave # that is the survey *not* a map
endmap
Then this thconfig:
layout local
code metapost
def l_survey_cave (expr P) =
T:=identity;
pickup PenC;
if ATTR__shotflag_splay:
thdraw P withcolor (1,0.5,0.5);
else:
thdraw P;
fi;
enddef;
endcode
endlayout
source "thecavearea.th"
select skeletonMEE@thecavearea
export map -proj extended -layout local -o "thecave-skeleton.pdf"
That gives me a PDF to see my design.
Now, once you are done, export a new XVI, just like I said for the
projected elevation, but this time use "extended" as your -projection.
Add a .th2 and add it to your .th in the same way (I call mine
"surveyeecustom" to show it is one I have customised), create scraps in
it as you would for a plan (I name mine somescrapSEE for Scrap Extended
Elevation, and use MEE for the maps). From there on, the instructions
are basically the same. However, I find that all too often, the
extending algorithm points a leg in completely the wrong direction. It
is much better than it used to be, but just randomly, it is nonsense. Or
it just scales the splays weird. So I often end up looking at it in
Survex Aven, seeing "that one looks wrong", then measuring from station
to splay in elevation or plan, to work out where it should have pointed,
and how far away. (It really depends how much you care.)
You will need to refer to the instructions for extended elevations, to
see what the "extend" options are. Some really useful stuff got added
relatively recently for scaling legs, so you can shrink a passage to 50%
of its natural length. And a tonne of other useful options.
If you want more than one variation of the extended elevation, eg. with
the leg folded left in one, and right in the other ... you are in for a
small nightmare, and I will let Bruce help you out, because he has a way
to do it. It is not straightforward, because Therion is really designed
to have just one extended elevation.
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