Rotate co ordinates by a rotation matrix.

Question

Andy 2013-4-4

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I have a set of x and y co ordinates which make up a random shape. I want to be able to rotate the shape 360 degrees in an animation. To do this i want to multiply the co ordinates by a rotation matrix and then i will set the co ordinates of the shape to these which will rotate the shape by that amount.

I have my rotation matrix

rot = [cos(5),sin(5);-sin(5),cos(5)];

and then i try to multiply the coordinates like this.

xCor = rot*xCor; yCor = rot*yCor;

I get an error saying the inner matrix dimensions must agree. How would i go about getting this to work, or is there a better way to achieve this?

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Answer 1

Kye Taylor 2013-4-4

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编辑：Kye Taylor 2013-4-4

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Is that 5 radians or 5 degrees you wish to rotate the points. If it's 5 degrees, I think you mean to have

rot = [cosd(5),sind(5);-sind(5),cosd(5)]

To answer your main question, what is the size of xCor and yCor? They should by 2 -by-N for some positive integer N.

However, I'm assuming that xCor is 1-by-N (x-coordinates of N points) and yCor is 1-by-N (y-coordinates of N points). If that is the case, try this instead

rData = rot*[xCor;yCor]; % compute 2-by-N array of rotated data
rXCor = rData(1,:); % extract x-coordinates of rotated data
rYCor = rData(2,:); % extract y-coordinates of rotated data