EXTEND(1)

✨ EXTEND(1) ✨

okay so bestie, welcome to extend, straight out of the Survex manual (section 1, if you're keeping track 💅). this little icon does exactly what its name says and nothing else: it produces an extended elevation. and honestly? it ate. let's get into it 🫶

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💖 NAME 💖

extend — produce an extended elevation ✨

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🎀 SYNOPSIS 🎀

extend [--survey=SURVEY] [--specfile=ESPEC_FILE] [--show-breaks]
INPUT_FILE [OUTPUT_3D_FILE]

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🦋 DESCRIPTION 🦋

so INPUT_FILE — the thing you hand it first — can be any of these:

• a Survex .3d file 📦
• a Compass .plt file 🧭
• a CMAP .sht file 🗺️

and lowkey here's the slay part: all Survex programs which read .3d files can also transparently handle these formats. no conversion era needed, it just works ✨

🌸 where does it start? the vibe check 🌸

if you don't pass a --specfile option (or its short option -p), extend starts with the highest station marked as an entrance which has at least one underground survey leg attached to it. main character station energy fr fr 👑

and if there are no such stations? it falls back to the highest deadend station in the survey — or, if there are no deadends at all, just the highest station. it always finds somebody to stan 💜

then here's what it does with that station:

• puts the first station on the left
• then folds each leg out individually to the right
• breaking loops arbitrarily (usually at junctions) 💀

🍓 output filename tea 🍓

if you don't specify the output filename, extend bases the output filename on the input filename — but it replaces the extension with _extend.3d. so like, for example:

extend deep_pit.3d produces an extended elevation called deep_pit_extend.3d 🌈

👑 the options, dish by dish 👑

• --survey=SURVEY, -s — restricts processing to the survey SURVEY including any sub-surveys. keeps things scoped bestie, no scope creep 🙈
• --show-breaks, -b — when you pass this, a leg flagged as "surface survey" gets added between each point at which a loop has been broken. this is very useful for visualising the result in aven. literally so helpful, iykyk 🔥

🧚 when simple isn't enough 🧚

ngl, this approach suffices for simple caves or sections of cave — but for more complicated situations, human intervention is required. it's giving "the algorithm tried its best" 😭

more complex sections of cave can be handled with a specfile, which gives directions to:

• switch the direction of extension between left and right
• explicitly specify the start station
• break the extension at particular stations or legs

⭐ the specfile, in all its glory ⭐

the specfile is in a format similar to cavern's data format. here's the whole vibe:

; This is a comment

; start the elevation at station entrance.a
*start entrance.a  ;this is a comment after a command

; start extending leftwards from station half-way-down.5
*eleft half-way-down.5

; change direction of extension at further-down.8
*eswap further-down.8

; extend right from further-down.junction, but only for
; the leg joining it to very-deep.1, other legs continuing
; as before
*eright further-down.junction  very-deep.1

; break the survey at station side-loop.4
*break side-loop.4

; break survey at station side-loop.junction but only
; for leg going to complex-loop.2
*break side-loop.junction complex-loop.2

ok real talk bestie: this approach requires some trial and error. but it gives useful results for many caves, so it's worth it 💪

and the most complex systems would benefit from an interactive interface to select and view the breaks and switches of direction. someday 🥲 for now, specfiles it is.

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🌈 SEE ALSO 🌈

aven(1), cavern(1), diffpos(1), dump3d(1), sorterr(1), survexport(1)

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💜 Copyright 💜

1998-2025

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and that's the whole page, bestie! 💖 it's from the Survex manual, dated Jun 23, 2026, page EXTEND(1) in section 1 — go extend something gorgeous ✨🎀🦋