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Last Modified: 2013-11-25

Compound matrix transformation [code attached]

Hello Experts,

I have the following code which shows the rotation of a 2D polygon and what i want is to modify it using a compound matrix transformation so that the square rotates about an arbitrary point.

Can anyone help me how can i do such a thing ??

Thanks in advance

close all;
clear all;
 
 
% a 2D pologyon 
p=[-1 1 1 -1 -1 ; -1 -1 1 1 -1];
 
% points p = in homogeneous coord
p(3,:)=1;
 
% axes for plotting the animation
figure; 
hold on;
axis([-6 6 -6 6]);
axis equal;
 
for theta=0:0.005:2*pi
 
    R=[cos(theta) -sin(theta) 0 ; sin(theta) cos(theta) 0 ; 0 0 1];
    
    pdash=R*p; 
    
    pdash(1,:)=pdash(1,:)./pdash(3,:);
    pdash(2,:)=pdash(2,:)./pdash(3,:);
    
    cla;
    plot(pdash(1,:),pdash(2,:),'b');   
    drawnow;
    
end

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perdoname_

Asked: 2008-10-09

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1 Solution

LVL 85

ozoCommented: 2008-10-11

http://www.skytopia.com/project/cube/matrix.html

LVL 4

SyfAldeenCommented: 2008-11-06

perdoname_,
Here you are the modified code:
You can learn more here:
Transforming Objects - MATLAB

function rotsquare
close all;
clear all;
 
% a 2D pologyon
p=[-1 1 1 -1 -1 ; -1 -1 1 1 -1];
 
% points p in XY plane
p(3,:)=0;
 
% points p = in homogeneous coord
p(4,:)=1;
 
% axes for plotting the animation
figure;
hold on;
axis([-6 6 -6 6]);
axis equal;
 
%Rotate about the upper right corner (1,1)
Tx1 = makehgtform('translate',[-1 -1 0]);
Tx2 = makehgtform('translate',[ 1  1 0]);
 
for theta=0:0.005:2*pi
    R=makehgtform('zrotate',theta);
    pdash=Tx2*R*Tx1*p;
    cla;
    plot(pdash(1,:),pdash(2,:),'b');
    drawnow;
end

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Compound matrix transformation [code attached]

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