[Therion] How to get the right count for cave lengths

[Tarquin Wilton-Jones]

Hi,

I have nearly completed the total survey for the system I am mapping. In
total, there are a series of little caves (actually mines, but I will
stick with the word "caves" because it is clearer), a blind surface
shaft, and a couple of significantly long caves. In total, these were
surveyed over a series of 6 trips. On one of those trips, we surveyed
the surface, and any short fragments of passage that we encountered that
way. One of those fragments turned out to be one of the major caves. The
major cave's survey was subsequently completed on another trip, but its
first few metres are included in the surface survey.

I am used to Survex. Each of the surveying trips has its own .th file:

overall.th ("input"s all the other files)
surface1/surface1.th (contains the entrances to several fragments, and
the first 2 legs of cave 1)
surface2/surface2.th (contains the blind shaft's plumbed depth and some
other entrances)
cave1/cave1.th (does not contain any entrances, but is a long cave,
connected to the "cave 1 legs" in surface1.th
cave2/cave2.th (contains the first part of cave2, and its entrance)
cave3/cave3.th (contains cave3, with two entrances)
cave2ext/cave2ext.th (contains the second part of cave2)

Cave1 is connected to cave2.

Each entrance is marked using "station 2 Cave1 entrance" in the
centreline section of the file where it is defined. Survex only displays
aggregate statistics. Therion tries to identify "caves", which is a
concept I am not used to.

I had hoped that Therion would be smart enough to see that caves are
connected to each other, and work out the connected lengths. But it
seems that it only works out the length of the files within the same
survey. Cave1 doesn't get any length. Cave2 gets only the length from
cave2.th - the length of the cave2ext and cave1 are not included.

How do I make Therion realise what caves are connected? Do I need to put
them into a structure like this?
survey overall
survey cave1_2 -entrance 2 at cave2 -name "Caves 1 and 2"
input cave1.th
input cave2.th
input cave2ext.th
endsurvey
endsurvey

And if so ... how do I tell it that *part* of the cave lies within the
surface survey file? Do I need to split the surface survey up into
parts, one of which is the entrance to cave1?

Separately, when using "statistics topo-length on", it ignores the
surface survey legs, which is quite unfair for the person who surveyed 1
km of surface to link all of the entrances - they get no credit at all.
Can it be asked to include surface legs in the topo-length calculations
for survey credits?

Thanks for any advice.

Tarquin