rotation matrix

Started by tsuraan April 09, 2002 11:18 AM

3 comments, last by tsuraan 22 years, 10 months ago

Author

122

April 09, 2002 11:18 AM

I have what should be an equation for a matrix that will rotate an arbitary vector around an axis defined by some other vector. The code that I am using is:


vec3 vec3::rotate3d(vec3 axis, float angle) {

        vec3 final;

        float c = (float)cos(angle);
        float s = (float)sin(angle);
        float t = (1.0f-(float)cos(angle));

        final.x = (t*axis.x*axis.x+c)*x+
                          (t*axis.x*axis.y+s*axis.z)*y+
                          (t*axis.x*axis.z-s*axis.y)*z;

        final.y = (t*axis.x*axis.y-s*axis.z)*x+
                          (t*axis.y*axis.y+c)*y+
                          (t*axis.y*axis.z+s*axis.x)*z;

        final.z = (t*axis.x*axis.y+s*axis.y)*x+
                          (t*axis.y*axis.z-s*axis.x)*y+
                          (t*axis.z*axis.z+c)*z;

        x = final.x;
        y = final.y;
        z = final.z;
        return *this;
}

When the axis is one of the cardinal axes (i, j, or k), this degenerates into the matrix that we are used to seeing, but if the axis is something else, the rotation doesn''t rotate correctly. Instead of the vector being in a plane, it seems to wobble considerably. Can anyone tell what I''m doing wrong here? I don''t really want to use quaternions, but if I can''t get this to work correctly I may have to. P.S. I''m not sure about the code tags. Would a preview option be possible for this forum?

Fruny

1,658

April 09, 2002 11:42 AM

OpenGL blue book p443 (glRotate)

The rotation matrix is :

| x2(1-c)+c  xy(1-c)-zs xz(1-c)+ys 0 || yx(1-c)+zs y2(1-c)+c  yz(1-c)-xs 0 || xz(1-c)-ys yz(1-c)+xs z2(1-c)+c  0 || 0          0          0          1 |

"Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it." — Brian W. Kernighan