[Therion] extend

Marco Corvi marco.corvi at gmail.com
Sun Jun 10 14:33:11 CEST 2018


i put together comments to all the posts
about "extend"

(1) yes, -1 = left, 1 = right and vert is in the middle (0)

(2) evaristo, with his proposal of idealized profile not only suggested a
way to control shortening, but that also allows stretching. that's good

(3) bruce described a procedure for a program to automatically decide how
to draw splays in the extended profile.
it's more or less what topodroid implements: at a station the range of
azimuths is divided into angular sectors one for each leg at that station.
a splay is "projected" using the leg of the sector its azimuth falls in.
(by the way, to really be in bad luck one need three vert in a row)

(4) a program may assign extends to splays automatically, but the user
should always be allowed to override what the program does.
(that's why a user can set extend also for splays, in topodroid)

(5) "cave length": in the (old) manuals i studied that the cave length is
"computed" measuring the length of an ideal line that goes thru the middle
of the passage.
now it is rather cumbersome to compute that line, and all the programs uses
the length of the midline, with some discount (duplicate in therion, L in
compass, and so on).
the problem, i think, is that cave length is not a thing that can be
well-defined.
so the numbers we give for cave length are an approximation of a fuzzy
concept.

marco
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