[討論] 找出兩條直線的交點

[middle1023 (米豆)]

小弟因為有需要
可是爬過文發現沒有人有這樣的問題
於是自己寫了一個  也順便分享出來
希望各位前輩也可以幫小弟找看看有沒有錯誤
還是說有更好的寫法

以下是code

function [x y] = crosspoint(line1,line2)
% This function can find the cross point with two straight lines
% Input matrix : line1 = [line1(x1),line1(y1) ; line1(x2),line1(y2)]
%                line2 = [line2(x1),line2(y1) ; line2(x2),line2(y2)]
%                x1,y1 and x2,y2 is the two end points of lines
% [x y] is the cross point of two straight lines

%%%%%%% test %%%%%%%%
line1 = [0.8,2.6 ; 6,9.4];
line2 = [5,-2 ; 2.55,8.45];
%%%%%%% test %%%%%%%%

x11 = line1(1,1); y11 = line1(1,2);
x21 = line1(2,1); y21 = line1(2,2);
x12 = line2(1,1); y12 = line2(1,2);
x22 = line2(2,1); y22 = line2(2,2);

%%%%%%% test %%%%%%%%
plot([x11 x21] ,[y11 y21]);hold on;plot([x12 x22] ,[y12 y22]);
%%%%%%% test %%%%%%%%

seta = 0; setb = 0;
% line1
if x11 == x21
    % for x = a y + b
    str1 = [num2str(x11) '=a*(' num2str(y11) ')+b'];
    str2 = [num2str(x21) '=a*(' num2str(y21) ')+b'];
    [aa1,bb1] = solve(str1,str2,'a','b');
    a1 = subs(aa1) ;  b1 = subs(bb1) ; seta = 1;
else % y11 == y21 or other
    % for y = a x + b
    str1 = [num2str(y11) '=a*(' num2str(x11) ')+b'];
    str2 = [num2str(y21) '=a*(' num2str(x21) ')+b'];
    [aa1,bb1] = solve(str1,str2,'a','b');
    a1 = subs(aa1) ; b1 = subs(bb1) ;
end
% line2
if x12 == x22
    % for x = a y + b
    str1 = [num2str(x12) '=a*(' num2str(y12) ')+b'];
    str2 = [num2str(x22) '=a*(' num2str(y22) ')+b'];
    [aa2,bb2] = solve(str1,str2,'a','b');
    a2 = subs(aa2) ; b2 = subs(bb2) ; setb = 1;
else % y12 == y22 or other
    % for y = a x + b
    str1 = [num2str(y12) '=a*(' num2str(x12) ')+b'];
    str2 = [num2str(y22) '=a*(' num2str(x22) ')+b'];
    [aa2,bb2] = solve(str1,str2,'a','b');
    a2 = subs(aa2) ; b2 = subs(bb2) ;
end
% solve   y = a*x + b
if seta == 1
    st1 = ['x=' num2str(a1) '*y+(' num2str(b1) ')'];
else
    st1 = ['y=' num2str(a1) '*x+(' num2str(b1) ')'];
end
if setb == 1
    st2 = ['x=' num2str(a2) '*y+(' num2str(b2) ')'];
else
    st2 = ['y=' num2str(a2) '*x+(' num2str(b2) ')'];
end
[xx,yy] = solve(st1,st2,'x','y');
x = subs(xx);
y = subs(yy);

%%%%%%% test %%%%%%%%
plot(x,y,'o','MarkerSize',3,'LineWidth',2);
%%%%%%% test %%%%%%%%

% program end


謝謝大家

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