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linecirc.m
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linecirc.m
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function [x,y]=linecirc(slope,intercpt,centerx,centery,radius)
%LINECIRC Find the intersections of a circle and a line in cartesian space
%
% [xout,yout] = LINECIRC(slope,intercpt,centerx,centery,radius) finds
% the points of intersection given a circle defined by a center and
% radius in x-y coordinates, and a line defined by slope and
% y-intercept, or a slope of "inf" and an x-intercept. Two points
% are returned. When the objects do not intersect, NaNs are returned.
% When the line is tangent to the circle, two identical points are
% returned. All inputs must be scalars
%
% See also CIRCCIRC
% Copyright 1996-2002 Systems Planning and Analysis, Inc. and The MathWorks, Inc.
% Written by: E. Brown, E. Byrns
% $Revision: 1.9 $ $Date: 2002/03/20 21:25:45 $
if nargin ~= 5; error('Incorrect number of arguments'); end
% Input consistency test
if ~isequal(size(slope),size(intercpt),size(centerx),size(centery),size(radius),[1,1])
error('Inputs must be scalars')
elseif ~isreal([slope intercpt centerx centery radius])
error('inputs must be real')
elseif radius<=0
error('radius must be positive')
end
% find the cases of infinite slope and handle them separately
if ~isinf(slope)
% From the law of cosines
a=1+slope.^2;
b=2*(slope.*(intercpt-centery)-centerx);
c=centery.^2+centerx.^2+intercpt.^2-2*centery.*intercpt-radius.^2;
x=roots([a,b,c])';
% Make NaN's if they don't intersect.
if ~isreal(x)
x=[NaN NaN]; y=[NaN NaN];
else
y=[intercpt intercpt]+[slope slope].*x;
end
% vertical slope case
elseif abs(centerx-intercpt)>radius % They don't intercept
x=[NaN;NaN]; y=[NaN;NaN];
else
x=[intercpt intercpt];
step=sqrt(radius^2-(intercpt-centerx)^2);
y=centery+[step,-step];
end