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View Full Version : How to make an Areosol Spray?


JohnDes
07-12-2004, 07:48 PM
Hello, I am working on an animation of an areosol spray and need some help on how to do it. I need to show the droplets up close so a gas won't rerally do. I am currently trying it with realflow but so far have met many disappointments with the product.

Thanks in advance.

sundialsvc4
07-19-2004, 03:11 AM
The spray emitted from an aerosol container is normally produced using what's called a particle system. This animation technique would be appropriate for the droplets.

Depending on the amount of realism you wish to achieve, you can composite this droplet particle-system with others whose materials produce the "gaseous" look caused by the droplets that are so fine you can't see them. Compositing also can help the spray look thicker.

All of these layers would be built on top of the model of the can itself, and layers which represent whatever hand/finger there might be, pressing on the button. The button itself, as it moves in the act of being pressed, might be a composite layer too.

Sandwich all these layers together and you've got a marvelous spray-can.

I think it would be very difficult to try to "do it all at once," in a single render, and of course it would be expensive. The complex motions of an aerosol spray-jet would be easily described as layers of motion.

JohnDes
07-20-2004, 09:25 PM
I appreciate the help, and your advice as a combo technique rather than an all in one render...work smarter not harder, right? Thanks!

uncon
07-20-2004, 11:40 PM
I would just make an emitter spray out like 10,000 points, link them to tiny hypervoxels (with a glass preset) and render in one pass. It might take a while but it would allow for complete fredom of movement and you could easily tweek the spray.

JohnDes
07-21-2004, 01:59 PM
Uncon, Thanks for the input, but I am a little confused on one point...passes. What do you mean by one pass...a typical RGB render or something else. I am unfamiliar with that term. Any when you say tweak the spray you mean like using the velocity to deform the drops in flight? Thanks again guys...I;ll send a post of what you helped with.

uncon
07-21-2004, 07:11 PM
By one pass I mean one straight render from lightwave. Not a particle pass composited on top of a geometry pass. The emiter would just control the spray geometry and the individual point velocities, you could use the hypervoxel properties to deform the individual drops.

I just did a quick test and with about 5,000 particles I got a nice spray with a bunch of 50mm drops at full spray it took 4min per frame to render out turning on anti-aliasing and motion blur to make it look believable. what's cool is with the hypervoxels you could fly-through the spray (or stop it) and inspect each individual drop if you wanted. The particles can refreact the background (not necessary from a distance) and cast shadows too.

JohnDes
07-22-2004, 12:34 AM
Uncon, thats exactly what I want to do...inspect the drops and see reflections and blurs in a believable scene...I have a favor to ask...would you be so kind as to send me your test scene? If not thats cool. Thanks for the lead in the right direction!

sundialsvc4
07-22-2004, 02:11 AM
I would just make an emitter spray out like 10,000 points, link them to tiny hypervoxels (with a glass preset) and render in one pass. It might take a while but it would allow for complete fredom of movement and you could easily tweak the spray.
I respectfully disagree. Obviously it is an individual artistic choice but it is my opinion that compositing in this case would have distinct advantages.
It's really overkill to individually model 10,000 points moving in space, just to achieve the effect of a spray. IMHO, of course. In a single particle system, all particles are alike. But in a spray jet, not only are the particles not alike, but much of the spray-effect is not created by visually-distinct "particles" anyway. If the effect can be produced very satisfactorily under conditions where a particle-system is not responsible for the entire effect, and that alternative promises to be computationally much less expensive, should it not be used? Let's hear it for two-dimensional techniques. Let's render two particle systems, just a short strip of each and thus be finished with our "3D" work. Now overlap these with "themselves, offset +2 and -2 frames in time." Do it again with a few different offsets. Voila! A thick, variable spray, as long as you like, all produced out of half-a-second or so of film. At 1/6th or less the original render time. Or less! And if you don't like it, you can tweak it considerably without 're-rendering' anything. To me that is very compelling.

uncon
07-22-2004, 08:28 PM
I trashed my scene, but if you PM me I can remake it and send you the scene, there are no objects in it or anything just an emitter that emits hypervoxels. It might take about 2 min to re-create. So I'll get to it, if you promise to show me what you are working on:) .

sundialsvc4,
I understand your point, but the goal was to get up close to individual droplets, yeah 10,000 is overkill but from a distance it would make a mist. My 5,000 particle test looked good and you can freeze the particles or make them move very slowly if you want to fly the camera through it slow-mo matrix like. You can vary the size of the individual droplets with hypervoxel controls and use the velocity to stretch them out if you wanted. Also, when hypervoxels don't touch they render really quickly even with refraction. This method, although more computationally expensive, has a greater flexibility as far as how close you want to get to it or the shape of the spray (if you have it linked to a moving sprayer).

uncon
07-22-2004, 08:29 PM
Oh, BTW I am using LW8, so let me know if that works with you.

JohnDes
07-22-2004, 09:06 PM
Thanks for the offer uncon, Here is what I am working on....this is a still from the animation...and as you can see the spray looks too thick after many tries I got it to look more "sprayish" but so far this is as good as I can get. I can get close to it, but my drops look to sharp and the deformation is not beleivable enough...any thoughts? If possible I am using LW 7.5...thanks again.

uncon
08-02-2004, 02:28 PM
You need some motion blur if you want the spray animated, and maybe it wouldn't hurt to add a layer of misty sprite hypervoxels. If you freeze an aerosaul in time all you will see is thousands of little round drops, which is what you should get with hypervoxels. I don't know if I am understanding the problem.

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