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       extend — produce an extended elevation from a .3d file


       extend  [--specfile configuration .espec file]   input .3d file [output
       .3d file]



              The extend program can also work on Compass .plt  (as  can  aven
              and any other Survex program which reads .3d files).

       If  no specfile 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

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

       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

See Also

       3dtopos(1),  aven(1),  cad3d(1),  cavern(1),  diffpos(1),   sorterr(1),