Not able to rotate an object in matlab?

hello there, I'm working on rotation matrices and want to rotate a spiral along some axis (any axis will do my job). I have written the following code for that, however its stretching and squeezing the spring and rotating arbitrarily. Please help

clear all
%close all

t = -5*pi:0.1:5*pi;

z = t
x = cos(t)
y = sin(t)
M = [x;y;z]
plot3(M(1,:),M(2,:),M(3,:),'LineWidth',1.5)

xlim([-3 3])
ylim([-3 3])
grid on

hold on;
H = line ([-3 3],[0 0])
set (H,'color','r','LineWidth',1)
H = line ([0 0],[-3 3])
set (H,'color','r','LineWidth',1)
H = line ([0 0],[0 0],[-20 20])
set (H,'color','r','LineWidth',1)

a = pi/2;
T = [ 1 0 0; 0 cos(a) -sin(a); 0 sin(a) cos(a)]

%T = [ 0.7071 0 -0.7071; 0 1 0; 0.7071 0 0.7071]

hold on;

S = T*M

plot3(S(1,:),S(2,:),S(3,:),'m')
xlabel ('x')
ylabel ('y')
zlabel ('z')

[Sean de Wolski]

Can you please clarify your question? What is it doing that you do/don't expect? What specifically do you want us to help you with? etc.

Answer 1

[Honglei Chen]

Hi Simar,

I think your program is doing what you want it to do, it rotates the whole thing 90 degrees in respect to the x axis. You probably don't see it because you are limiting your axis to [-3 3] in both x and y direction. Remove the xlim and ylim in your code and you will see the result in scale.

Of course, if you want to rotate it according to an arbitrary axis, then there are more to do to build the rotation matrix.