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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...

createCircle(varargin)
function circle = createCircle(varargin)
%CREATECIRCLE Create a circle from 2 or 3 points
%
%   C = createCircle(P1, P2, P3);
%   Creates the circle passing through the 3 given points. 
%   C is a 1*3 array of the form: [XC YX R].
%
%   C = createCircle(P1, P2);
%   Creates the circle whith center P1 and passing throuh the point P2.
%
%   Works also when input are point arrays the same size, in this case the
%   result has as many lines as the point arrays.
%
%   Example
%   % Draw a circle passing through 3 points.
%     p1 = [10 15];
%     p2 = [15 20];
%     p3 = [10 25];
%     circle = createCircle(p1, p2, p3);
%     figure; hold on; axis equal; axis([0 50 0 50]);
%     drawPoint([p1 ; p2; p3]);
%     drawCircle(circle);
%
%   See also:
%   circles2d, createDirectedCircle
%
%   ---------
%   author : David Legland 
%   INRA - TPV URPOI - BIA IMASTE
%   created the 31/10/2003.
%


if nargin == 2
    % inputs are the center and a point on the circle
    p1 = varargin{1};
    p2 = varargin{2};
    x0 = p1(:,1);
    y0 = p1(:,2);
    r = hypot((p2(:,1)-x0), (p2(:,2)-y0));
    
elseif nargin == 3
    % inputs are three points on the circle
    p1 = varargin{1};
    p2 = varargin{2};
    p3 = varargin{3};

    % compute circle center
    line1 = medianLine(p1, p2);
    line2 = medianLine(p1, p3);
    point = intersectLines(line1, line2);
    x0 = point(:, 1); 
    y0 = point(:, 2);
    
    % circle radius
    r = hypot((p1(:,1)-x0), (p1(:,2)-y0));
end
    
% create array for returning result        
circle = [x0 y0 r];

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