MATLAB: How to rotate a line

linerotat

Is there a way to rotate a line of 30 degree? For example: x=1; y=[2 4 6 8 10];
Does it require a center point of rotation?(example center point is [2,6])Or does it requires the center of the line?
Thanks.

Best Answer

This should answer your question. This code does what you want and shows you what happens depending on your choice of centre point of rotation. (Look up rotation matrices and direction cosine matrices for more information). This is an example for 3D rotation for 2D in the plane you could simplify and only use the Rz part.
Kevin
clear all; close all; clc;
%Example coordinates
y=[2 4 6 8 10];
x=ones(size(y));
%Vertices matrix
V=[x(:) y(:) zeros(size(y(:)))];
V_centre=mean(V,1); %Centre, of line
Vc=V-ones(size(V,1),1)*V_centre; %Centering coordinates
a=30; %Angle in degrees
a_rad=((a*pi)./180); %Angle in radians
E=[0  0 a_rad]; %Euler angles for X,Y,Z-axis rotations
%Direction Cosines (rotation matrix) construction
Rx=[1        0        0;...
    0        cos(E(1))  -sin(E(1));...
    0        sin(E(1))  cos(E(1))]; %X-Axis rotation
Ry=[cos(E(2))  0        sin(E(2));...
    0        1        0;...
    -sin(E(2)) 0        cos(E(2))]; %Y-axis rotation
Rz=[cos(E(3))  -sin(E(3)) 0;...
    sin(E(3))  cos(E(3))  0;...
    0        0        1]; %Z-axis rotation
R=Rx*Ry*Rz; %Rotation matrix
Vrc=[R*Vc']'; %Rotating centred coordinates
Vruc=[R*V']'; %Rotating un-centred coordinates
Vr=Vrc+ones(size(V,1),1)*V_centre; %Shifting back to original location
figure;
plot3(V(:,1),V(:,2),V(:,3),'k.-','MarkerSize',25);  hold on; %Original
plot3(Vr(:,1),Vr(:,2),Vr(:,3),'r.-','MarkerSize',25); %Rotated around centre of line
plot3(Vruc(:,1),Vruc(:,2),Vruc(:,3),'b.-','MarkerSize',25); %Rotated around origin
axis equal; view(3); axis tight; grid on;
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