In article <3982371C.528B2E10@peak.edu.ee>, Margus Ramst 
<mar### [at] peakeduee> wrote:

> Firstly: at least to me, the jitter value seems to have a 
> disproportionately strong effect. If I use more jitter than around 
> 0.03 in my spray (quite fast flow at a tight angle), the particles go 
> all over the place. I understand that increased speed > greater 
> movement per iteration > greater jitter influence, but in my case 
> (the "Absudity" scene) the flow speed is 1.2 - not outrageously fast 
> IMO. Just a minor problem, but still I wonder...

The jitter value in the particle_system block? Greater velocity should 
reduce the influence...and a ratio of 1.2 to 0.03 should be quite a 
small amount of jitter.


> Also, I tried both a little animation and motion blurring the 
> particles. In both cases the system seems too erratic to give the 
> illusion of 'flow', particles jump around and *seem* to disappear at 
> a random age?! Might be some misunderstanding on my part, but it's a 
> relatively simple system with narrow angle, long lifespan and very 
> low jitter. The animations were 4 frames per TU, so it shouldn't look 
> all that choppy. I am not wrong in assuming that animation is done 
> simply through the 'time' parameter, am I?

To get the best results, the ratio of iterations to time should remain 
constant, so you must increase iterations along with time. Otherwise, 
the accuracy of the simulation changes in different frames, leading to 
different results, and making the particles unpredictable.


> About the 'lifespan' value: is it measured in time units or iterations? 

It is measured in time units.


> And even if I set 'lifespan' much larger than both time and 
> iterations, I still get the "n particles destroyed" message after a 
> simulation. What does that mean?

It just means that when the particle_simulation was destroyed, that many 
particles were left over and destroyed as well. It was just an aid to 
help detect memory leaks...if your lifespan is larger than time, no 
particles will die, and all will be left over to be destroyed.


> And, could you add output of the number of particles in the scene?

I plan to add output of final number and maximum number.


> Finally, 'cause I'm just too lazy to test <g>: how are the particles 
> arranged for the get_particle index, newest to oldest or vice versa? 
> I would like to have the same index number always assigned to the 
> same particle, at any point in time, but with all the creation and 
> destruction this seems iffy.

Ehh, I'm not really sure. :-)
It should be newest particles at the beginning, and oldest at the end, I 
think. If particles die in the simulation, then the indices will 
change...I can't avoid this. It might be possible to give particles 
unique ID's or to allow you to track a specific particle, though.

-- 
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/
TAG Web page: http://tag.povray.org/

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