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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John VanSickle <evi### [at] KOSHERhotmailcom> wrote:

>
> 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.

Just a fanciful depiction, to give a bit more life to the scene. But it makes me
wonder if there are physical laws preventing such a body (Earth's moon, for
example) from rotating that fast. Would it fly apart?

Neutron stars are known to rotate extremely rapidly. But then again, they are
extremely dense, with tremendous gravitational forces holding them together.

Off topic: It would be interesting to know what a neutron star 'looks like' if
we could actually see one CU through a telescope. Since it's only neutrons (no
full atoms with electrons), and since light is an electromagnetic phenomenon,
what happens when a photon impinges on it? Light needs electrons to 'react' with
when it hits an object, AFAIU. An interesting 'thought experiment.'

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John VanSickle <evi### [at] KOSHERhotmailcom> wrote:

>
> ...the 180 degree blurring has
> one benefit:  You only have to render half as many frames to achieve the
> same level of blurring.
>

Yes indeed. My animation code block is set up to do that as well; but for this
animation I originally rendered *all* the motion, as I didn't think of posting a
'180-deg version' until later. Then it was just a simple matter of skipping
frames during the averaged re-rendering. BTW, the re-rendering process goes
*fast*, as it can be run at POV-Ray's lowest-quality setting. Just images
projected on the front of a box, with ambient 1.0.  Not very *elegant*, but
extremely useful.

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Alain <kua### [at] videotronca> wrote:

>
> 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.

When I was a kid, I made lots of 8mm home movies--nutty science-fiction stuff
and animation--and the funny thing is, this technique never occurred to me at
the time! Yet it's so simple.

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John VanSickle <evi### [at] KOSHERhotmailcom> wrote:

>
> 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.

I think I may have used the phrase 'collision detection' by mistake. The
meteoroids in my scene actually *are* static, BTW (except for rotations); the
camera just flies through 'em. What I meant earlier was that I was trying to
find a method to keep them from simply 'overlapping.' But I forgot the correct
term for that. :-[  Uh, obviously, I still can't remember it...

I actually did run a different kind of test animation, just for fun, with the
meteors all zipping through space in random directions. The result was total
chaos! The camera's point of view couldn't really lock onto anything, no real
reference. (You would think that the moon and the background would have served
that purpose; but all those flying objects made the scene way too disorienting.)

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> John VanSickle <evi### [at] KOSHERhotmailcom> wrote:
>
>>
>> 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.
>
> Just a fanciful depiction, to give a bit more life to the scene. But it makes me
> wonder if there are physical laws preventing such a body (Earth's moon, for
> example) from rotating that fast. Would it fly apart?
>
> Neutron stars are known to rotate extremely rapidly. But then again, they are
> extremely dense, with tremendous gravitational forces holding them together.
>
> Off topic: It would be interesting to know what a neutron star 'looks like' if
> we could actually see one CU through a telescope. Since it's only neutrons (no
> full atoms with electrons), and since light is an electromagnetic phenomenon,
> what happens when a photon impinges on it? Light needs electrons to 'react' with
> when it hits an object, AFAIU. An interesting 'thought experiment.'
>
>
>

If a body spin to fast, it won't be able to condense into a planet or 
moon. There is a point where it can, theoreticaly, form into an almost 
pancake shape...
If it get accelerated, by some obscure mean, it can fly apart.

For the neutron star, you'll see the incandecent gaz cloud that could be 
called it's athmosphere, or have degenerated into a solid crust but 
still stay "normal" matter.
If you where to remove that outer layer to reveal the all neutron core, 
well, it may be perfectly transparent, only detectable by the 
gravitational bending of light... There is also the possibility that 
there is not enough place for the photons to squeeze through. What appen 
when a photon hit a neutron square on? There could be some reflection...



Alain

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Alain <kua### [at] videotronca> wrote:

>
> If a body spin to fast, it won't be able to condense into a planet or
> moon. There is a point where it can, theoreticaly, form into an almost
> pancake shape...


Ah, I didn't think of that: At such a fast rotation rate, there would have been
no Moon to begin with! (The only thing I can think of that would cause a Moon to
spin faster *once it was formed* would be, say, a near-miss from some other,
bigger object, with a much larger gravitational field. But that would have torn
the Moon apart again, probably.)
>
> For the neutron star, you'll see the incandecent gaz cloud that could be
> called it's athmosphere, or have degenerated into a solid crust but
> still stay "normal" matter.
> If you where to remove that outer layer...

Ah, right again. The neutron star, with its huge gravitational and magnetic
fields, would obviously attract all the other loose matter in it's
vicinity--forming a crust. So it may never be possible to see a 'naked' neutron
star. And the photon question becomes merely a hypothetical one.

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