Rotation of a set of points

Question

Rasmus 2014-2-25

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/119061-rotation-of-a-set-of-points

回答： Mischa Kim 2014-2-25

采纳的回答： Mischa Kim

I am given 4 points, each is a corner of a plane to a box.

p1=[0;0] p2=[sqrt(3/4);-1/2] p3=[sqrt(3/4);1/2] p4=[0;1]

I want to rotate the plane counterclockwise with 120- and240 degree. so that i get a box of some sort.

-------

what i try to do is to make a matrix of the first plane, give the rows x and y varribles and plot them in.

>> fill(x1,y1,'r')

which works fine.

now i want to rotate it with 120 degree. so i make a rotation matrix

theta= 120

R=[cos(theta) -sin(theta); sin(theta) cos(theta)]

I multiply it with the previously matrix, and put new varriables on the new matrix, like x2 and y2

fill(x1,y1,'r',x2,y2,'g')

for some reason it does not obbey my command :S

any tips and trick?

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Answer 1

Mischa Kim 2014-2-25

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/119061-rotation-of-a-set-of-points#answer_126116

在 MATLAB Online 中打开

Rasmus, this should work:

X     = [p1 p2 p3 p4];
theta = 120*(pi/180);
R     = [cos(theta) -sin(theta); sin(theta) cos(theta)];
Xr1   = R*X;
theta = 240*(pi/180);
R     = [cos(theta) -sin(theta); sin(theta) cos(theta)];
Xr2   = R*X;
hold on
fill(X(1,:),X(2,:),'r')
fill(Xr1(1,:),Xr1(2,:),'b')
fill(Xr2(1,:),Xr2(2,:),'k')
grid; box;
axis square