> A 1280X720 animation, 600 frames, of the camera flying through some space
> debris. It has motion-blur but no antialiasing. (I thought I could get away
> without AA due to the erratic and blurred camera motions, which will usually
> hide the lack of AA--but the moon still shows some jaggies every now and then.)

Very nice!

Some minor issues

- the lighting is very soft / ambient for a space scene
- there seem to be some "collisions" (rocks passing through each other)
- this better be debris from a recently destroyed moon, otherwise
   so-called astroid belts / fields usually have millions of km
   between individual asteroids ;)

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Christian Froeschlin <chr### [at] chrfrde> wrote:

>
> Very nice!

Thanks!
>
> Some minor issues
>
> - the lighting is very soft / ambient for a space scene

Yes indeed. By design, actually. I wanted an 'old' 1960's era
science-fiction-film look for the scene. Like it was photographed in a studio
setting. But the one thing I adamantly refused to do was to show the strings
holding up the meteors ;-)

> - there seem to be some "collisions" (rocks passing through each other)

I was wondering if anyone would notice that. So far, I count only one, but there
are probably others. I toyed with the idea of writing some kind of code for
collision detection or whatever, but got bogged down in the details; so I opted
for an easier scheme of random meteor placement, but one that's not *quite* so
simple as <rand(...),rand(...),rand(...)>. The final construction is actually a
cylindrical 'tube' full of objects (with a central tube carved out for the
camera to move through.) There are multiple seed() values for this, to give me
at least *some* control over the situation. If I had taken enough time, I could
probably have found a set of values to *totally* eliminate the few collisions.
But real collision detection is obviously needed.

> - this better be debris from a recently destroyed moon, otherwise
>    so-called astroid belts / fields usually have millions of km
>    between individual asteroids ;)

It's just a completely fanciful scene. That's why I wasn't even sure what to
call those rocks. Not asteroids, not really meteors--more a collection of simple
space junk. But why would they all be *rotating* and at different rates? Hmm,
something strange here!  :-P

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Kenneth wrote:

> But the one thing I adamantly refused to do was to show the strings
> holding up the meteors ;-)

such a scene would likely be shot with the camera pointing vertically up
through a glass plate and then dropping a bucket of cardboard rocks ;)

> It's just a completely fanciful scene. That's why I wasn't even sure what to
> call those rocks. Not asteroids, not really meteors

certainly not meteors, but you probably meant meteroids :-P

http://www.freemars.org/jeff/meteor/

> But why would they all be *rotating* and at different rates?

That I find believable, space stuff rotates. In case of a break-up
the angular momentum of the parent body has to be preserved, but the
rotation of each individual piece is very much a result of its mass,
shape, original position, and random collision history.

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Christian Froeschlin wrote:

> certainly not meteors, but you probably meant meteroids :-P

and even more likely you meant meteOroids ;)

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Christian Froeschlin <chr### [at] chrfrde> wrote:
>
> such a scene would likely be shot with the camera pointing vertically up
> through a glass plate and then dropping a bucket of cardboard rocks ;)

Hey, good idea! I need to remember that... :-P
>
> > It's just a completely fanciful scene. That's why I wasn't even sure what to
> > call those rocks. Not asteroids, not really meteors
>
> certainly not meteors, but you probably meant meteroids :-P
>

Oh. You're right.

>
> > But why would they all be *rotating* and at different rates?
>
> That I find believable, space stuff rotates. In case of a break-up
> the angular momentum of the parent body has to be preserved, but the
> rotation of each individual piece is very much a result of its mass,
> shape, original position, and random collision history.

My scene does looks like an explosion of something. But there's no 'central
explosion point'; the meteors--oops, meteoroids--are just hanging there in
space, doing their thing. Hey, I just thought of a plausible(??) reason for the
random rotations: a mutual gravitational tug-of-war! On second thought, though,
that's not likely; they would eventually join together into a lumpy asteroid.

Oh well. This scene takes place in "a galaxy far far away"-- different physics
there ;-)

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Kenneth wrote:

> Christian Froeschlin <chr### [at] chrfrde> wrote:

>> such a scene would likely be shot with the camera pointing vertically up
>> through a glass plate and then dropping a bucket of cardboard rocks ;)
> 
> Hey, good idea! I need to remember that... :-P

I recall reading that's how they did space explosions in Star Trek ;)

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Christian Froeschlin <chr### [at] chrfrde> wrote:


>
> I recall reading that's how they did space explosions in Star Trek ;)

And the Death Star explosion in the original STAR WARS. Sadly(??), that's all
been supplanted by CGI now, for the most part. (Although, I keep coming across
modern examples of 'real' flame elements and such being used in movies;
apparently it's *still* sometimes more expedient to film real elements vs.
trying to synthesize the effect with computer algorithms.)

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> Kenneth wrote:
>
>> Christian Froeschlin <chr### [at] chrfrde> wrote:
>
>>> such a scene would likely be shot with the camera pointing vertically up
>>> through a glass plate and then dropping a bucket of cardboard rocks ;)
>>
>> Hey, good idea! I need to remember that... :-P
>
> I recall reading that's how they did space explosions in Star Trek ;)

That's how they did all realistic space explosions, those where you 
don't see smoke going up and debrits going down...
Some samples:
The original Star war trilogy.
The original StarTreck.
The original Battlestar Galactica.

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On 1/16/2013 4:27 AM, Kenneth wrote:
> A 1280X720 animation, 600 frames, of the camera flying through some space
> debris. It has motion-blur but no antialiasing. (I thought I could get away
> without AA due to the erratic and blurred camera motions, which will usually
> hide the lack of AA--but the moon still shows some jaggies every now and then.)
>
> I rendered 6000 original frames, then (also in POV-Ray) averaged-together
> batches of 20 to get each final frame. The resulting motion-blur is 'full
> blur'--meaning, it's as if the movie camera had a 360-degree shutter (i.e.,
> always open.) No real film camera does that, though.  So I'll also post a
> version that corresponds to a 'standard' 180-degree shutter. It might be
> interesting to compare the subtle 'subjective experience' between the two.

I've done both kinds of motion blur in my own work.  While the 360 
degree blurring does look more like real life (and more like videos that 
are shot on video tape instead of on film), the 180 degree blurring has 
one benefit:  You only have to render half as many frames to achieve the 
same level of blurring.

I do however note that the moon is rotating much faster than any 
spherical body will in real life.  The earth, for instance, rotates one 
degree every four minutes.  For most purposes that makes the earth 
appear to be standing still.

Regards,
John

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On 1/21/2013 5:28 AM, Kenneth wrote:

>> - there seem to be some "collisions" (rocks passing through each other)
>
> I was wondering if anyone would notice that. So far, I count only one, but there
> are probably others. I toyed with the idea of writing some kind of code for
> collision detection or whatever, but got bogged down in the details; so I opted
> for an easier scheme of random meteor placement, but one that's not *quite* so
> simple as <rand(...),rand(...),rand(...)>. The final construction is actually a
> cylindrical 'tube' full of objects (with a central tube carved out for the
> camera to move through.) There are multiple seed() values for this, to give me
> at least *some* control over the situation. If I had taken enough time, I could
> probably have found a set of values to *totally* eliminate the few collisions.
> But real collision detection is obviously needed.

Actually you can get away without collision detection on a fly-through 
like this by simply having each asteroid stay in place, and have the 
camera take a more winding route.  The spinning of the asteroids and the 
motion of the camera will help hide the cheating.  After an asteroid 
belt has been in place for a few thousand years, the relative motion of 
the asteroids is minimal.

(If the asteroids are moving relative to each other, then they will 
collide.  This will cause a loss of energy--converted into heat--which 
will cause one or both of the asteroids involved to fall out of orbit.)

If you still want to have a few asteroids moving through the field, then 
code a few non-intersecting cylinders at varying angles, add a 
spherical-sweep path for your camera, and then  fill the space around 
them with non-intersecting spheres.  Put stationary asteroids where the 
spheres are located and have the moving asteroids move along the axes of 
the cylinders.  (Don't put the cylinders or spheres into the scene, just 
have code calculate where they should go.)

Regards,
John

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