How to rotating a stl object

Hi everyone,

I know this question has already been asked but here I am trying to spin the rotor of a wind turbine. I have the stl file and I applied the rotation matrix but the object is rotating but also in translation. My objective is simply to make it turn on the spot. Thanks for your advices.

[p,t,tnorm]=import_stl_fast('Rotor.stl',1,2);
TR=triangulation(t,p);
%trimesh(TR)
 
   ax=linspace(0,2*pi,10);
  
   az=pi/4;
   ay=pi/4;
   
   Ry=[cos(ay) 0 sin(ay); 0 1 0; -sin(ay) 0 cos(ay)];
   Rz=[cos(az) -sin(az) 0; sin(az) cos(az) 0;  0 0 1];
   filename='test.gif';
   figure;
  
    h1=trisurf(t,p(:,1),p(:,2),p(:,3), ...
       'FaceColor','black','EdgeColor','none','LineWidth',0.25);
   
for idx=1:length(ax)
   Rx=[ 1 0 0; 0 cos(idx) -sin(idx); 0 sin(idx) cos(idx)];
   PointR=p*Rx;
   
   
  
   h1=trisurf(t,PointR(:,1),PointR(:,2),PointR(:,3), ...
       'FaceColor','black','EdgeColor','none','LineWidth',0.25);
   %view(90,0)
        frame = getframe(1);
      im = frame2im(frame);
      [imind,cm] = rgb2ind(im,256);
      if idx == 1
          imwrite(imind,cm,filename,'gif', 'Loopcount',inf);
      else
          imwrite(imind,cm,filename,'gif','WriteMode','append');
      end
      pause(0.1)
end

I have attached the stl file

[Simon Chan]

Check this: https://www.mathworks.com/matlabcentral/fileexchange/30864-3d-rotation-about-shifted-axis

[TOM SALIC]

Thank you. I have checked the link and try to use the function but it doesn't work.

[Jan]

If you explain, what "doesn't work" means, it is possible to help you. Do you get an error message? Does the result differ from your expectations?

[TOM SALIC]

Sorry.

No I have no error but the result is the same as before. I specified the axis of rotation in the "AxelRot" function. But the stl object keeps moving off its axis of rotation.

 ax=linspace(0,2*pi,10);
 [p,t,tnorm]=import_stl_fast('Rotor.stl',1,2);
TR=triangulation(t,p);
filename='test.gif';

figure;
% x=[-13.30 100]; y=[0 0]; z=[89.35 89.35];
% line(x,y,z);

for idx=1:length(ax)
[PointR, R, t1] = AxelRot(p(:,:)',ax(idx)*(180/pi), [1 0 0],[-13.30 0 89.35]);
%  bhold on;
h1=trisurf(t,PointR(1,:),PointR(2,:),PointR(3,:), ...
       'FaceColor','black','EdgeColor','none','LineWidth',0.25);
   view(90,180)
        frame = getframe(1);
      im = frame2im(frame);
      [imind,cm] = rgb2ind(im,256);
      if idx == 1
          imwrite(imind,cm,filename,'gif', 'Loopcount',inf);
      else
          imwrite(imind,cm,filename,'gif','WriteMode','append');
      end
      pause(0.1)
end

I have attached the gif after the result.

Answer 1

[Fabio Freschi]

You shoud translate the points p before the rotation and then move them back

If R is your rotation matrix and the center of rotation is C = [0 Cy, Cz] (Cy and Cz identify the center of the turbine rotor)

PointR = (p-C)*R+C

[TOM SALIC]

Perfect !! it's work ! thank you @Fabio Freschi and others for the advices and solutions.