Date: Jan 27, 2013 11:48 PM
Author: Roger Stafford
Subject: Re: Quicker way to rotate a 3 dimensional array?
"Phil " <matlab@test.com> wrote in message <ke4thb$s7j$1@newscl01ah.mathworks.com>...

> I've got an array that is three dimensional where the first two dimensions are relatively large numbers and the third has length 3. This third one contains x,y,z co-ordinates that I would like to rotate about the x axis. I've managed to do this using:

>

> tmp3 = tmp;

> k = 0;

> for i=1:height

> for j=1:width

> k = k + 1;

> tmp3(i,j,:) = reshape(tmp(i,j,:),1,3)*[1,0,0;0,cos(theta),sin(theta);0,-sin(theta),cos(theta)];

> end

> end

>

> This works but as it's iterating, it's quite slow. Is there a faster way to do this?

- - - - - - - - - -

Assuming theta is a scalar try this:

tmp3 = tmp;

tmp3(:,:,2) = tmp(:,:,2)*cos(theta)-tmp(:,:,3)*sin(theta);

tmp3(:,:,3) = tmp(:,:,2)*sin(theta)-tmp(:,:,3)*cos(theta);

Roger Stafford