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scripts/general/polyarea.m

changeset 10289: 4b124317dc38
parent:1bf0ce0930be
author: John W. Eaton <jwe@octave.org>
date: Tue Feb 09 20:58:55 2010 -0500 (60 minutes ago)
permissions: -rw-r--r--
description: base_properties::set_children: account for hidden children 
     1## Copyright (C) 1999, 2006, 2007, 2009 David M. Doolin

     2##

     3## This file is part of Octave.

     4##

     5## Octave is free software; you can redistribute it and/or modify it

     6## under the terms of the GNU General Public License as published by

     7## the Free Software Foundation; either version 3 of the License, or (at

     8## your option) any later version.

     9##

    10## Octave is distributed in the hope that it will be useful, but

    11## WITHOUT ANY WARRANTY; without even the implied warranty of

    12## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

    13## General Public License for more details.

    14##

    15## You should have received a copy of the GNU General Public License

    16## along with Octave; see the file COPYING.  If not, see

    17## <http://www.gnu.org/licenses/>.

    18

    19## -*- texinfo -*-

    20## @deftypefn {Function File} {} polyarea (@var{x}, @var{y})

    21## @deftypefnx {Function File} {} polyarea (@var{x}, @var{y}, @var{dim})

    22##

    23## Determines area of a polygon by triangle method.  The variables

    24## @var{x} and @var{y} define the vertex pairs, and must therefore have

    25## the same shape.  They can be either vectors or arrays.  If they are

    26## arrays then the columns of @var{x} and @var{y} are treated separately

    27## and an area returned for each.

    28##

    29## If the optional @var{dim} argument is given, then @code{polyarea}

    30## works along this dimension of the arrays @var{x} and @var{y}.

    31##

    32## @end deftypefn

    33

    34## todo:  Add moments for centroid, etc.

    35##

    36## bugs and limitations:  

    37##        Probably ought to be an optional check to make sure that

    38##        traversing the vertices doesn't make any sides cross 

    39##        (Is simple closed curve the technical definition of this?). 

    40

    41## Author: David M. Doolin <doolin@ce.berkeley.edu>

    42## Date: 1999-04-14

    43## Modified-by: 

    44##    2000-01-15 Paul Kienzle <pkienzle@kienzle.powernet.co.uk>

    45##    * use matlab compatible interface

    46##    * return absolute value of area so traversal order doesn't matter

    47##    2005-10-13 Torsten Finke

    48##    * optimization saving half the sums and multiplies

    49

    50function a = polyarea (x, y, dim)

    51  if (nargin != 2 && nargin != 3)

    52    print_usage ();

    53  elseif (size_equal (x, y))

    54    if (nargin == 2)

    55      a = abs (sum (x .* (shift (y, -1) - shift (y, 1)))) / 2;

    56    else

    57      a = abs (sum (x .* (shift (y, -1, dim) - shift (y, 1, dim)), dim)) / 2;

    58    endif

    59  else

    60    error ("polyarea: x and y must have the same shape");

    61  endif

    62endfunction

    63

    64%!shared x, y

    65%! x = [1;1;3;3;1];

    66%! y = [1;3;3;1;1];

    67%!assert (polyarea(x,y), 4, eps)

    68%!assert (polyarea([x,x],[y,y]), [4,4], eps)

    69%!assert (polyarea([x,x],[y,y],1), [4,4], eps)

    70%!assert (polyarea([x,x]',[y,y]',2), [4;4], eps)