NAME

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

SYNOPSIS

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

Description

       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
       junctions).

       If the output filename is not specified, extend writes  its  output  to
       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 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

       3dtopos(1),   aven(1),  cad3d(1),  cavern(1),  diffpos(1),  printdm(1),
       printhpgl(1),   printpcl(1),   printps(1),   sorterr(1),    svxedit(1),
       xcaverot(1)

                                                                     extend(1)