NAME

       extend - produce an extended elevation

SYNOPSIS

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

DESCRIPTION

       INPUT_FILE  can  be a Survex .3d file, a Compass .plt file or a CMAP .sht file (all Survex programs which
       read .3d files can also transparently handle these formats).

       If no --specfile option (or short option -p) is given, extend starts with the highest station  marked  as
       an entrance which has at least one underground survey leg attached to it.  If there are no such stations,
       the  highest  deadend  station  in  the survey (or the highest station if there are no deadends) is used.
       Extend puts the first station on the left, then folds each leg out individually to  the  right,  breaking
       loops arbitrarily (usually at junctions).

       If  the  output  filename  is  not specified, extend bases the output filename on the input filename, but
       replacing the extension with _extend.3d. For example, extend deep_pit.3d produces an  extended  elevation
       called deep_pit_extend.3d.

       The  --survey=SURVEY  option  (short  option  -s) restricts processing to the survey SURVEY including any
       sub-surveys.

       If you pass --show-breaks (short option -b) then a leg flagged as "surface survey" will be added  between
       each point at which a loop has been broken - this can be very useful for visualising the result in aven.

       This  approach  suffices  for simple caves or sections of cave, but for more complicated situations human
       intervention is required.  More complex sections of cave can be handled with a specfile giving directions
       to switch the direction of extension between left and right, to explicitly specify the start station,  or
       to break the extension at particular stations or legs.

       The specfile is in a format similar to cavern's data format:

          ; 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

       This  approach  requires some trial and error, but gives useful results for many caves.  The most complex
       systems would benefit from an interactive interface to  select  and  view  the  breaks  and  switches  of
       direction.

SEE ALSO

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

COPYRIGHT

       1998-2025

                                                  Feb 21, 2025                                         EXTEND(1)