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

       1998-2024

                                           Aug 14, 2024                                 EXTEND(1)