----- Original Message ----- From: "Fred Klingener" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Saturday, March 09, 2002 3:13 PM Subject: Re: [JAVA3D] Rotations
> > >1. Points are P1 and P2 > > >2. length of cylinder L = |P2 - P1| > > >3. desired unit vector along axis of cylinder V = (P2 - P1)/L > > >4. midpoint of line M = (P1 + P2)/2> > . . . > > >5. Construct cylinder Shape3D cyl = new Shape3D . . . > > > I forget what axis the Java 3D primitive Cylinder lines up on, say > it's the > > > X-axis, X. > > > . . . > > >7. Find rotation axis S = X cross V; // don't normalize it here. > > Transform3D t3d = new Transform3D(new Quat4d(S.x, S.y, S.z, X dot V), new > Vector3d(M), 1.0); This is, of course, wrong. Yet another argument for an immediate 'undo' on the email 'send' button. *sigh* Required form of the quat is (n*sin(theta/2), cos(theta/2)), so we probably have to work through sin(theta/2) = ((1 - (X dot V))/2)^1/2 cos(theta/2)= ((1 + (X dot V))/2)^1/2 Now, I think I'll shut up at least until I can see whether this actually works and whether it really doesn't have worse quadrant problems than arccos. Cheers, Fred =========================================================================== To unsubscribe, send email to [EMAIL PROTECTED] and include in the body of the message "signoff JAVA3D-INTEREST". For general help, send email to [EMAIL PROTECTED] and include in the body of the message "help".
