In article <3973D2BD.A92017E7@peak.edu.ee>, Margus Ramst 
<mar### [at] peakeduee> wrote:

> Yes, but is this really worth the computational expense? I suspect 
> the spin of individual particles has little perceptible effect on the 
> overall behaviour a large particle system.

It may, especially when you have a large number of particles with the 
same spin bouncing off of an object. And what if the particles are 
*supposed* to represent a large number of large objects?
As for the computational expense...it should, of course, be able to be 
turned off. Maybe a simple "angular_forces on/off" flag.

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In article <397### [at] hotmailcom>, Pabs <pab### [at] hotmailcom> 
wrote:

> I think when considering *Solid Particles* or balls/spheres we are 
> getting out of the _particle_ domain (aren't particles 1D not 3D) & 
> into the physics of solid objects a bit more, which is a lot more 
> complex than that of particles.

A 1D particle would be a point on a line, with no mass, no velocity, 
etc. Not very useful.
And there is no reason to restrict particles to points...it is just that 
inter-particle collisions aren't necessary or wanted in liquid 
simulations.

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Christopher James Huff - Personal e-mail: chr### [at] maccom
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In article <397### [at] peakeduee>, Margus Ramst 
<mar### [at] peakeduee> wrote:

> Strange, it sometimes happens without running ipf previously 
> (although that seems to be a sure-fire way). Haven't found the 
> connection yet.

It still sounds like an uninitialized variable or a dangling pointer.


> I see. Actually, I think this is sufficient in most cases, especially 
> with liquids.

Inter-particle collisions would probably just interfere with liquid-like 
behavior.


> As for the "solid" particles - I don't think inter-particle collision 
> and deflection would be at all expensive for spherical particles, and 
> prohibitively expensive for most other shapes.

Actually, the only way I can think of doing it would also work for 
arbitrary shaped objects(like meshes), but would be computationally 
expensive for all of them. I suppose the cheapest one would be a 
triangle, followed by triangle pairs, other simple, non-solid shapes, 
and boxes. Spheres would definitely not be the cheapest.
I definitely need to learn more about rigid body dynamics before I try 
this.


> What physical properties would be needed? Collision is easy, 
> deflection and impact energy absorption too, friction I'm not so sure 
> about... What else?

Impact energy absorption already exists, as elasticity. Friction 
coefficient, shatter speed, geometry, etc. Internally, center of 
gravity, angular velocity, a bounding box...


> BTW, I found an interesting page discussing sorting algorithms for 
> particle systems (specifically kd-trees and Barnes-Hut trees). I saw 
> no actual code, but pretty informative nevertheless. The URL is:
> http://physics.gmu.edu/~large/lr_forces/lr_general.html

Thanks, I will take a look...

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Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
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