Camera spin
17 messages in this thread
In addition to what Martin said about keyframing a 180-degree roll, you can
also try linking everything in your scene to a dummy rotating the dummy
90-degrees on frame 0. This will likely shift the entire animation to an
orientation in which you won't ever being passing the camera over the
singularity at the poles. Note that the singularity is just an artifact of
quanternion mathematics, which was originally developed in the 1800's to
inhibit the gimbles on big sailing ships from locking. All high-end 3D
animation systems use this form of math for smooth motion, but like anything
it's not perfect.
– G
PMJI- I've been a little out in the woods on this flip thing, too..
I seem to be having a similar problem w/ a camera movement in R2. I
found that when I dive the camera down the inside of an open-ended
cylinder it jerks a 180 deg roll every 8th frame or so. Very
puzzling, it was. I tried doing the reverse-roll-at-the-frame
maneuver to counteract it and started getting into complicated
keyframe manipulation that seemed a little.. well, excessive.
Is this the same sort of thing? Are there "singularities" imbedded
somewhere in the walls of my cylinder, as well, yanking the camera
this way & that?
My workaround was to simply throw out the offending camera
path/keyframes and leave it stationary, while making the cylinder
shrink down its length from one end, giving the illusion of camera
movement. Seems to work OK, sort of. It kinda flies in the face,
tho, of advice I received in a 3D animation course for this kind of
motion, i.e., "Move the camera & leave the objects alone if
possible..".
(BTW are they by any chance the same kind of singularities that black holes
become, a la Stephen Hawking…? (<g>juskiddin)).
Best regards, John Gummere =SP=
John, it sounds like you're diving straight down the vertical axis, and since
the quaternion singularity IS that axis, you should rotate your entire scene so
that you're diving down any other axis (and you'll be fine).
– G
PS: No need to worry about black holes. <g>
gary: i have also had this problem with the camera movment. can you
explain the axis and rotation of the objects a in a little more
detail. i dont think i get the picture with the present
explenations. thanks ara
Quaternion math (used by almost every animation system on the planet
for things like camera and object rotations) is polar-based (using a
three-component vector and an angle/scaler), which causes a
singularity along the polar axis. As the vector approaches that
singularity, its orientation becomes ambiguous. In order to deal
with the ambiguity, the program maintains continuity of motion (or at
least tries to minimize discontinuities). This math was originally
developed in the early 1800's to keep the gimbles on huge sailing
ships from locking as they traversed their own polar singularities.
If you're interested in learning more about it, check out an article
in Computer Graphics & Applications magazine (the ACM Siggraph bible)
by Ken Shoemake, 1985. He pretty much pioneered the use of them in
computer animation while at Xerox Parc (as far as I can remember).
There is a strong relationship between quaternion math and Euler's
theorem, which states something about how any displacement of an
object with a fixed centroid can be represented by a single rotation
about an arbitrary axis.
I hope that gives you more of what you wanted, but reading over it I'm
starting to doubt that's what you had in mind when you asked the
question. The short answer is that it's just the way it works.
Duuhhh?!#@*IK^&)>>Y^ERR$||!++<…… . . . . . . .
ara p.s. thanks for the reply. >:-)
>> Quaternion math … is polar-based … which causes a singularity
along the polar axis. As the vector approaches that singularity, its
orientation becomes ambiguous. In order to deal with the ambiguity,
the program maintains continuity of motion (or at least tries to
minimize discontinuities) … keep the gimbles on huge sailing ships
from locking as they traversed their own polar singularities …
Euler's theorem, which states something about how any displacement of
an object with a fixed centroid can be represented by a single
rotation about an arbitrary axis.
Earth to Yost! Earth to Yost! 'Sounds like Data describing the
Ambiguous Temporal Singularity on Star Trek tonite…(did I forget to
turn off the T.V….) <g>
Geez…….I had no idear that all that stuff was in my little ol' 3DS
camera. Good job Gary, another good reason I am only a user and not
a writer!
PMJI, but I'm just curious – I can see this method as advantageous
with objects, but a problem with cameras due to the "normal"
orientation of framing a shot. Is this true ? I don't even pretend to
understand this stuff, but I'm still curious none the less <g>.
There's no real difference between objects and cameras. The orientation is
vague along the singularity in both cases. You'll notice that Wavefront, Alias
and Softimage all do exactly the same thing that we do.
– G
I just thought that with cameras, having a "preferred direction"
(keeping the framing "normal") might be a problem, where it wouldn't
be a problem with object rotations. I didn't mean that 3DS was any
different in it's implementation, I was just curious about quaternion
interpolation in general. I not sure why <g>.
I can recommend a few good books about quaternion's if you're interested
(they're about 1000 pages each).
– G
Sure, I'd like to know about the books. Like I said, I won't even
pretend to understand the math itself, but for some reason I like to
read this stuff – to get what I can out of it. As a matter of fact, I
found a couple of books today with Quaternion references. Interesting
story of how the guy that "discovered" them in the 1800's, after 10
years of searching for a second imaginary axis with 2 imaginary
components, had a flash of inspiration walking past a bridge or
something, and realized he needed three. That I can understand <g>.
BILL
Eureka, it's a bridge!
I'll email the references to you after I get them from Dan.
– G
So it's kind of like saying that every direction from the north pole is south?
>>As the vector approaches that singularity, its orientation becomes
>>ambiguous.
Dave
That at least captures the spirit of the vagueness of it.
– G