Info Catalog octave: Voronoi Diagrams octave: Geometry octave: Interpolation on Scattered Data

octave: Convex Hull

 
 30.3 Convex Hull
 ================
 
 The convex hull of a set of points is the minimum convex envelope
 containing all of the points.  Octave has the functions ‘convhull’ and
 ‘convhulln’ to calculate the convex hull of 2-dimensional and
 N-dimensional sets of points.
 
  -- : H = convhull (X, Y)
  -- : H = convhull (X, Y, OPTIONS)
      Compute the convex hull of the set of points defined by the arrays
      X and Y.  The hull H is an index vector into the set of points and
      specifies which points form the enclosing hull.
 
      An optional third argument, which must be a string or cell array of
      strings, contains options passed to the underlying qhull command.
      See the documentation for the Qhull library for details
      <http://www.qhull.org/html/qh-quick.htm#options>.  The default
      option is ‘{"Qt"}’.
 
      If OPTIONS is not present or ‘[]’ then the default arguments are
      used.  Otherwise, OPTIONS replaces the default argument list.  To
      append user options to the defaults it is necessary to repeat the
      default arguments in OPTIONS.  Use a null string to pass no
      arguments.
 
DONTPRINTYET       See also: convhulln XREFconvhulln, *notedelaunay:
DONTPRINTYET       See also: convhulln XREFconvhulln, delaunay

      XREFdelaunay, voronoi XREFvoronoi.
 
  -- : H = convhulln (PTS)
  -- : H = convhulln (PTS, OPTIONS)
  -- : [H, V] = convhulln (...)
      Compute the convex hull of the set of points PTS.
 
      PTS is a matrix of size [n, dim] containing n points in a space of
      dimension dim.
 
      The hull H is an index vector into the set of points and specifies
      which points form the enclosing hull.
 
      An optional second argument, which must be a string or cell array
      of strings, contains options passed to the underlying qhull
      command.  See the documentation for the Qhull library for details
      <http://www.qhull.org/html/qh-quick.htm#options>.  The default
      options depend on the dimension of the input:
 
         • 2D, 3D, 4D: OPTIONS = ‘{"Qt"}’
 
         • 5D and higher: OPTIONS = ‘{"Qt", "Qx"}’
 
      If OPTIONS is not present or ‘[]’ then the default arguments are
      used.  Otherwise, OPTIONS replaces the default argument list.  To
      append user options to the defaults it is necessary to repeat the
      default arguments in OPTIONS.  Use a null string to pass no
      arguments.
 
      If the second output V is requested the volume of the enclosing
      convex hull is calculated.
 
DONTPRINTYET       See also: convhull XREFconvhull, *notedelaunayn:
DONTPRINTYET       See also: convhull XREFconvhull, delaunayn

      XREFdelaunayn, voronoin XREFvoronoin.
 
    An example of the use of ‘convhull’ is
 
      x = -3:0.05:3;
      y = abs (sin (x));
      k = convhull (x, y);
      plot (x(k), y(k), "r-", x, y, "b+");
      axis ([-3.05, 3.05, -0.05, 1.05]);
 

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