polygonLength

POLYGONLENGTH Perimeter of a polygon.

   L = polygonLength(POLYGON);
   Computes the boundary length of a polygon. POLYGON is given by a N-by-2
   array of vertices. 

   Example
     % Perimeter of a circle approximation
     poly = circleToPolygon([0 0 1], 200);
     polygonLength(poly)
     ans =
         6.2829

   See also:
   polygons2d, polygonCentroid, polygonArea, drawPolygon, polylineLength

0001 function len = polygonLength(poly, varargin)
0002 %POLYGONLENGTH Perimeter of a polygon.
0003 %
0004 %   L = polygonLength(POLYGON);
0005 %   Computes the boundary length of a polygon. POLYGON is given by a N-by-2
0006 %   array of vertices.
0007 %
0008 %   Example
0009 %     % Perimeter of a circle approximation
0010 %     poly = circleToPolygon([0 0 1], 200);
0011 %     polygonLength(poly)
0012 %     ans =
0013 %         6.2829
0014 %
0015 %   See also:
0016 %   polygons2d, polygonCentroid, polygonArea, drawPolygon, polylineLength
0017 %
0018 
0019 %   ---------
0020 %   author : David Legland
0021 %   INRA - TPV URPOI - BIA IMASTE
0022 %   created the 11/05/2005.
0023 %
0024 
0025 %   HISTORY
0026 %   2011-03-31 add control for empty polygons, code cleanup
0027 %   2011-05-27 fix bugs
0028 
0029 % If first argument is a cell array, this is a multi-polygon, and we simply
0030 % add the lengths of individual polygons
0031 if iscell(poly)
0032     len = 0;
0033     for i = 1:length(poly)
0034         len = len + polygonLength(poly{i});
0035     end
0036     return;
0037 end
0038 
0039 % case of a polygon given as two coordinate arrays
0040 if nargin == 2
0041     poly = [poly varargin{1}];
0042 end
0043 
0044 % check there are enough points
0045 if size(poly, 1) < 2
0046     len = 0;
0047     return;
0048 end
0049 
0050 % compute length
0051 if size(poly, 2) == 2
0052     % polygon in dimension 2 (classical case)
0053     dp = diff(poly([1:end 1], :), 1, 1);
0054     len = sum(hypot(dp(:, 1), dp(:, 2)));
0055 else
0056     % polygon of larger dimension
0057     len = sum(sqrt(sum(diff(poly([2:end 1], :), 1, 1).^2, 2)));
0058 end