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survex - cave surveying and mapping software…  more info»


extend(1)                                                  extend(1)

       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

       If no specfile is given, extend starts with the highest  sta‐
       tion 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 individu‐
       ally 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 deep_pit_extend.3d.

       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 sta‐
       tions 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 bene‐
       fit from an interactive interface  to  select  and  view  the
       breaks and switches of direction.

See Also
       3dtopos(1),   aven(1),   cad3d(1),   cavern(1),   diffpos(1),
       sorterr(1), svxedit(1)

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