09-06-2005, 03:52 AM

Hi,

I hope someone can help me. I'm trying to work out the coordinates of my object after it's been rotated around an arbitrary axis, but I'm having problems working out the maths I need to apply.

I know it's very easy to rotate around a fixed axis, e.g. the Z axis with the vector 0,0,1, by using:

x' = x*cos q - y*sin q

y' = x*sin q + y*cos q

z' = z

But what if, for example, you have an axis around the vector: 0, 0.7071607, 0.7071607 (i.e. 45 degrees between Y and Z).

You can't use a simple rotation matrix like the one above because it won't do the same thing!

So how exactly do you work it out?! I'm going out of my mind....

Any help appreciated. :)

Thanks.

Kaye

I hope someone can help me. I'm trying to work out the coordinates of my object after it's been rotated around an arbitrary axis, but I'm having problems working out the maths I need to apply.

I know it's very easy to rotate around a fixed axis, e.g. the Z axis with the vector 0,0,1, by using:

x' = x*cos q - y*sin q

y' = x*sin q + y*cos q

z' = z

But what if, for example, you have an axis around the vector: 0, 0.7071607, 0.7071607 (i.e. 45 degrees between Y and Z).

You can't use a simple rotation matrix like the one above because it won't do the same thing!

So how exactly do you work it out?! I'm going out of my mind....

Any help appreciated. :)

Thanks.

Kaye