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geom2d

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geom2d

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13 Jun 2005 (Updated )

Geometry library for matlab. Performs geometric computations on points, lines, circles, polygons...

ellipseToPolygon(ellipse, N)
function varargout = ellipseToPolygon(ellipse, N)
%ELLIPSETOPOLYGON Convert an ellipse into a series of points
%
%   P = ellipseToPolygon(ELL, N);
%   converts ELL given as [x0 y0 a b] or [x0 y0 a b theta] into a polygon
%   with N edges. The result P is (N+1)-by-2 array containing coordinates
%   of the N+1 vertices of the polygon.
%   The resulting polygon is closed, i.e. the last point is the same as the
%   first one.
%
%   P = ellipseToPolygon(ELL);
%   Use a default number of edges equal to 72. This results in one point
%   for each 5 degrees.
%   
%   [X Y] = ellipseToPolygon(...);
%   Return the coordinates of vertices in two separate arrays.
%
%
%   See also:
%   ellipses2d, drawEllipse, circleToPolygon, rectToPolygon
%
%   ---------
%   author : David Legland 
%   INRA - TPV URPOI - BIA IMASTE
%   created the 06/04/2005.
%

% HISTORY
% 2011-03-30 use angles in degrees, add default value for N
% 2011-12-09 rename to ellipseToPolygon

% default value for N
if nargin < 2
    N = 72;
end

% angle of ellipse
theta = 0;
if size(ellipse, 2) > 4
    theta = ellipse(:,5);
end

% get ellipse parameters
xc = ellipse(:,1);
yc = ellipse(:,2);
a  = ellipse(:,3);
b  = ellipse(:,4);

% create time basis
t = linspace(0, 2*pi, N+1)';

% pre-compute trig functions (angles is in degrees)
cot = cosd(theta);
sit = sind(theta);

% position of points
x = xc + a * cos(t) * cot - b * sin(t) * sit;
y = yc + a * cos(t) * sit + b * sin(t) * cot;

% format output depending on number of a param.
if nargout == 1
    varargout = {[x y]};
elseif nargout == 2
    varargout = {x, y};
end

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