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So you have been talking about the twists of the rubik's cube, where I
have been talking about the xyz components of Euler rotations.
Brent McPherson wrote:
Andre,
Order of rotations always matters. It is a mathematical consequence of how rotations are defined. (and not something we can work around in this universe anyway ;-)
If you rotate the top face of the cube by 90 degrees and then the left face by 90 degress you will get a different result than rotating the left face followed by the top face. Using quaternions doesn't change this fundamental fact.
I think you are confusing different things. Yes, quaternions have some very nice properties (for interpolation) but it doesn't help when you have stacked rotations. (as in a transform hierarchy)
--
Brent
-----Original Message-----
From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of André Adam
Sent: Thursday, November 01, 2007 12:15 PM
To: XSI(at)Softimage.COM
Subject: Re: rubik's cube
-snip-
"Quaternions are not a magic bullet for rotations. It is simply a different way of interpolating between two orientations.
The problem with the Rubik's cube rig is not the interpolation but rather the fact that for rotations the order of operations is important"
-snip-
Not really, the trick about quaternions is that there is no order of
operations, and the path of interpolation is always a straight line. In
Euler space, order of operations and interpolation depend on each other.
Brent McPherson wrote:
Quaternions are not a magic bullet for rotations. It is simply a different way of interpolating between two orientations.
The problem with the Rubik's cube rig is not the interpolation but rather the fact that for rotations the order of operations is important and if we perform a rotation A followed by rotation B it will be very different than if we applied B first and then rotation A.
Therefore, the crux of the Rubik's cube rig (which seems to be a thread that comes up for every 3D application at some point) is how we apply a series of rotations to the cube one after the other. Therefore, most solutions I have seen involve stacking all the rotations that are applied to the cube.
I haven't seen one as elegant and animator friendly as Helge's solution though!
--
Brent
-----Original Message-----
From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of André Adam
Sent: Thursday, November 01, 2007 7:59 AM
To: XSI(at)Softimage.COM
Subject: Re: rubik's cube
Depends on the rotation distance you are keyframing. If you rotate a
section by 270°, quaternions will make that a -90° move. You would then
have to set multiple keyframes on the way as a path guidance for the
quaternion math, with all those hassles regarding the fcurve
visualisation of quaternions introduced.
-André
Andy Nicholas wrote:
What would happen if you converted the keys to quaternions? Wouldn't that
solve it?
Andy
Be careful, that should pretty much immediately get you into gimbal lock
trouble.
-André
pingo van der brinkloev wrote:
ok I got a really easy solution.
Make 9 boxes and distribute them 3x3x3 (the cube)
select all the cubes and center their center in 0,0,0
Now you can select sides and rotate them and it works like it should.
Just remember to flatten the animation keys.
cheers!
pingo
On 31/10/2007, at 14.47, Adam Seeley wrote:
Oop, went too soon,
How about .... lattices that cover each of the 6 sides, which are
then applied during each rotation, frozen and removed after the
animation?
Again, not very interactive or scrubbable.
Adam.
-----Original Message-----
From: owner-xsi(at)Softimage.COM
[mailto:owner-xsi(at)Softimage.COM] On Behalf Of Adam Seeley
Sent: 31 October 2007 13:38
To: XSI(at)Softimage.COM
Subject: RE: rubik's cube
How about
-----Original Message-----
From: owner-xsi(at)Softimage.COM
[mailto:owner-xsi(at)Softimage.COM] On Behalf Of Oz Adi
Sent: 31 October 2007 13:35
To: XSI(at)Softimage.COM
Subject: Re: rubik's cube
thanks guys, for the info.
I've already tried the freeze transforms idea, and it does
work, the
only thing that bothers me is, when the client want to change some
animation, it should be a nightmare (I need to do a 25-30
sec one shot
animation)
To try and improve this method,
I am thinking of having a square curve near each of the
cube's side,
and a ppg with 6 boolean switches, each switch for each
sqaure curve,
as the animator, it's my responsibility to make sure, only
one switch
can be on in a given time.
Then have a scop on each little cube, to check which switch
in on, and
rotate with it's corresponding square curve this is of course, some
kind of a "simulation", meaning I cannot scrub the
timeline, because
the little cubes has no keyframes.
image: http://www.ozadi.com/pix/rubiks.jpg
but maybe after the animation is approved I can plot their
transfomrs.
what do you think?
Joe Laffey wrote:
On Wed, 31 Oct 2007, kim aldis wrote:
You can pull them apart easily enough if you want to see
how they
work. Peel the colours off and you'll see the screws
that hold it
together.
No need to remove screws to take the Rubik's apart. Just
turn one side
45 degrees, and then either stick a flathead screwdriver, or your
thumb under the middle cube of the row and lift.
I am sure there is Google/YouTube reference for this.
--
Joe Laffey | Visual Effects for Film
and Video
LAFFEY Computer Imaging |
-------------------------------------
St. Louis, MO | Show Reel
http://LAFFEY.tv/?e07635
USA
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