Thread Subject:

Quicker way to rotate a 3 dimensional array?

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?

"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

"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

R = [ 1,0,0; 0,cos(theta),sin(theta); 0,-sin(theta),cos(theta)]

[nx ny nz] = size(temp);
temp3 = reshape(reshape(temp,[],3)*R, [nx ny 3]);

% Bruno

"Bruno Luong" <b.luong@fogale.findmycountry> wrote in message <ke59fr$8uo$1@newscl01ah.mathworks.com>...
> "Phil " <matlab@test.com> wrote in message <ke4thb$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
>
> R = [ 1,0,0; 0,cos(theta),sin(theta); 0,-sin(theta),cos(theta)]
>
> [nx ny nz] = size(temp);
> temp3 = reshape(reshape(temp,[],3)*R, [nx ny 3]);
>
> % Bruno

Perfect, I dropped this in and it worked right away and sped up the code considerably. I couldn't get Roger's solution to work unfortunately.