source: git/trunk/doc/extend.sgml @ 7bb8184

Last change on this file since 7bb8184 was 7bb8184, checked in by Olly Betts <olly@…>, 13 years ago

Retagging 1.2.0

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1<refmeta>
2<refentrytitle>extend</refentrytitle>
3<manvolnum>1</manvolnum>
4</refmeta>
5
6<refnamediv>
7<refname>extend</refname>
8<refpurpose>produce an extended elevation from a &x3d; file
9</refpurpose>
10</refnamediv>
11
12<refsynopsisdiv>
13<cmdsynopsis>
14<command>extend</command>
15<arg choice="opt">--specfile configuration .espec file</arg>
16<arg choice="req">&nbsp;input .3d file</arg>
17<arg choice="opt">output .3d file</arg>
18</cmdsynopsis>
19</refsynopsisdiv>
20 
21<refsect1><title>Description</title>
22
23<Note>
24<Para>
25The <command>extend</command> program can also work on
26<Application>Compass</Application> <filename>.plt</filename> (as can
27<command>aven</command> and any other &survexsuite; program which reads &x3d;
28files).
29</Para>
30</Note>
31
32<Para>
33If no specfile is given, extend starts with the highest station marked
34as an entrance which has at least one underground survey leg attached
35to it.  If there are no such stations, the highest deadend station in
36the survey (or the highest station if there are no deadends) is used.
37Extend puts the first station on the left, then folds each leg out
38individually to the right, breaking loops arbitrarily (usually at
39junctions).</Para>
40
41<Para>If the output filename is not specified, extend bases the output
42filename on the input filename, but ending "_extend.3d".  For example,
43<command>extend deep_pit.3d</command> produces an extended elevation
44called <filename>deep_pit_extend.3d</filename>.</Para>
45
46<Para>
47This approach suffices for simple caves or sections of cave, but for more
48complicated situations human intervention is required.  More complex
49sections of cave can be handled with a specfile giving directions to
50switch the direction of extension between left and right, to
51explicitly specify the start station, or to break the extension at
52particular stations or legs. </Para>
53
54<Para>
55The specfile is in a format similar to cavern's data format:</Para>
56
57<programlisting>
58;This is a comment
59
60; start the elevation at station entrance.a
61*start entrance.a  ;this is a comment after a command
62
63; start extending leftwards from station half-way-down.5
64*eleft half-way-down.5
65
66; change direction of extension at further-down.8
67*eswap further-down.8
68
69; extend right from further-down.junction, but only for
70; the leg joining it to very-deep.1, other legs continuing
71; as before
72*eright further-down.junction  very-deep.1
73
74; break the survey at station side-loop.4
75*break side-loop.4
76
77; break survey at station side-loop.junction but only
78; for leg going to complex-loop.2
79*break side-loop.junction complex-loop.2
80</programlisting>
81
82<Para>
83This approach requires some trial and error, but gives useful results
84for many caves.  The most complex systems would benefit from an
85interactive interface to select and view the breaks and switches of
86direction.</Para>
87
88</refsect1>
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