"Kenneth" <kdw### [at] gmailcom> wrote:
>
> ...I'm working up a 'better' example-- with a
> few new realistic constraints added. I'll post that asap.
>

Two of THESE animation examples are what my own mind's eye wants to see in
POV-Ray, for free-fall.

I actually like all three, but I like B) and C) better.  The two-axis rotation
of C) *might* not be physically correct, but it looks cool anyway ;-)

The red dot represents the 'center of mass' of the object (just a guess, of
course), and the rotations are around that point. Those 'off-center' rotations
automatically make the result look more realistic, IMO.

For the two-axis rotation, it looks like the 'degree' of one or the other needs
to be constrained, possibly so that the two do not exceed a certain ratio(?).
1:1? 1:0.5?  Otherwise, maybe that's when the odd 'reversed rotation' appearance
starts showing up?

For finding the *actual* center-of-mass (for a simulated POV-Ray animation
anyway), I think there might be a relatively simple scheme based on the 'reduced
mass' concept I previously mentioned. (That concept at its simplest takes two
separated masses-- like two Suns orbiting each other-- and comes up with a
single mass, the rotation point for the pair.) Even though my animated object is
a *single* object, it's made of simple separate parts. The *individual* parts
could be thought of as separate Suns (in a step-by-step fashion for the
computations?) Anyway, although a POV-Ray object has no real 'mass', that can be
simulated too (for an object made of simple geometric parts like spheres,
cylinders, etc.) Assuming that the parts are all made of the same stuff--the
same density--, the VOLUMES of the parts can be a stand-in for their separate
masses. And the volumes can be computed from the surface area(s).

So far, it's just an interesting set of ideas, that I haven't tried working out
yet.
---------------

The codes for the animation examples (a 400-frame animation):
A)
object{OBJ
rotate <-4000,0,0>*clock
rotate 360*rand(S) // arbitrary rotation
  }

B)
object{OBJ
rotate 360*rand(S) // arbitrary rotation
rotate <-4000,0,0>*clock
rotate 360*rand(S) // arbitrary rotation
  }

C)
object{OBJ
rotate <-4000,0,0>*clock
rotate 360*rand(S) // arbitrary rotation
rotate 800*clock*y
rotate 360*rand(S) // arbitrary rotation
  }

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