椭圆检测_椭圆检测_椭圆检测_matlab_椭圆拟合

function [varargout]=ellipsefit(x,y) %ELLIPSEFIT Stable Direct Least Squares Ellipse Fit to Data. % [Xc,Yc,A,B,Phi,P]=ELLIPSEFIT(X,Y) finds the least squares ellipse that % best fits the data in X and Y. X and Y must have at least 5 data points. % Xc and Yc are the x- and y-axis center of the ellipse respectively. % A and B are the major and minor axis of the ellipse respectively. % Phi is the radian angle of the major axis with respect to the x-axis. % P is a vector containing the general conic parameters of the ellipse. % The conic representation of the ellipse is given by: % % P(1)*x^2 + P(2)*x*y + P(3)*y^2 + P(4)*x + P(5)*y + P(6) = 0 % % S=ELLIPSEFIT(X,Y) returns the output data in a structure with field names % equal to the variable names given above, e.g., S.Xc, S.Yc, S.A, S.B, % S.Phi and S.P % % Reference: R. Halif and J. Flusser, "Numerically Stable Direct Least % Squares FItting of Ellipses," Department of Software Engineering, Charles % University, Czech Republic, 2000. % Conversion from conic to conventional ellipse equation inspired by % fit_ellipse.m on MATLAB Central % D.C. Hanselman, University of Maine, Orono, ME 04469 % Mastering MATLAB 7 % 2005-02-28 % Rotation angle fixed 2005-08-09 %-------------------------------------------------------------------------- x=x(:); % convert data to column vectors y=y(:); if numel(x)~=numel(y) || numel(x)<5 error('X and Y Must be the Same Length and Contain at Least 5 Values.') end D1=[x.*x x.*y y.*y]; % quadratic terms D2=[x y ones(size(x))]; % linear terms S1=D1'*D1; S2=D1'*D2; [Q2,R2]=qr(D2,0); if condest(R2)>1.0e10 warning('ellipsefit',... 'Data is Poorly Conditioned and May Not Represent an Ellipse.') end T=-R2\(R2'\S2'); % -inv(S3) * S2' M=S1+S2*T; CinvM=[M(3,:)/2; -M(2,:); M(1,:)/2]; [V,na]=eig(CinvM); c=4*V(1,:).*V(3,:) - V(2,:).^2; A1=V(:,c>0); P=[A1; T*A1]; % correct signs if needed P=sign(P(1))*P; Phi=atan(P(2)/(P(3)-P(1)))/2; c=cos(Phi); s=sin(Phi); % rotate the ellipse parallel to x-axis Pr=zeros(6,1); Pr(1)=P(1)*c*c - P(2)*c*s + P(3)*s*s; Pr(2)=2*(P(1)-P(3))*c*s + (c^2-s^2)*P(2); Pr(3)=P(1)*s*s + P(2)*s*c + P(3)*c*c; Pr(4)=P(4)*c - P(5)*s; Pr(5)=P(4)*s + P(5)*c; Pr(6)=P(6); % extract other data XcYc=[c s;-s c]*[-Pr(4)/(2*Pr(1));-Pr(5)/(2*Pr(3))]; Xc=XcYc(1); Yc=XcYc(2); F=-Pr(6) + Pr(4)^2/(4*Pr(1)) + Pr(5)^2/(4*Pr(3)); AB=sqrt(F./Pr(1:2:3)); A=AB(1); B=AB(2); Phi=-Phi; if A<B % x-axis not major axis, so rotate it pi/2 Phi=Phi-sign(Phi)*pi/2; A=AB(2); B=AB(1); end S.Xc=Xc; S.Yc=Yc; S.A=A; S.B=B; S.Phi=Phi; S.P=P; if nargout==1 varargout{1}=S; else outcell=struct2cell(S); varargout=outcell(1:nargout); end