Breath Vapor Simulation in Maya
An intermediate level tutorial involving Particles and Dynamics
By Dariush Derakhshani

Page 1 of 3

More and more, cold weather scenes are being shot in mild climates, or in enclosed studios for budgetary, temporal and comfort reasons. Since the climate on these shoots is not cold, we lose the little natural nuances of reality. Therefore, it becomes incumbent on the special effects department to add these little nuances to add to the sceneís overall believability.

One major nuance to contend with in such a shoot is the visibility of breath vapor when an actor or animal exhales in the cold climate. To that end, it has become the job of the soda caffeine-addled animator to add digitally created breath vapor to these actors or animals to further the illusion need for the scene. [an error occurred while processing this directive] This tutorial will take you through a setup and animation to simulate breath vapor in a cold climate. Using a downloaded preview clip from Eyewire.com, I have a scene with two women walking as they talk to each other, down a city street during a cold day. My task is to add breath vapor to each of them through the 90 frame shot. I will assume for this tutorial that you already know how to get around Maya, so Iíll cut to the chase.

Figure 1.
I will leave out all the drudgery of setting up your camera and importing your images, as they will differ from task to task. This particular scene requires me to have a 320x240 render region with a perspective camera set to a 35mm TV Projection film gate.

Once I have the images loaded into my image plane as an animated sequence, I have to track the camera to the background. Itís an annoying task, but most definitely necessary to get a good shot going. Figure 1.

Once I have a quick shot of whiskey with a tequila chaser, Iím ready to begin. I start first by creating a directional particle emitter. I use a directional so I can funnel the particles in any particular direction. Omni emitters donít work so well here.

Judging from the way the women are facing, I set up my emitterís direction axis to spew particles away from their faces. In this case it would be primarily in the positive Z with a little negative X to boot: Direction X = Ė0.3; Direction Y = 0; Direction Z = 1.

I turn the rate of the emitter to 0, for now, so I can track the emitter to the womanís mouth without having particles everywhere. And, to make life easier, I create a locator, which I scale up to make it big and noticeable on my screen, color it red, and center it
Figure 2.
directly on the emitter. I group the emitter under the locator by middle mouse button dragging it in the Outliner window to the Locator node, which I have named Anim_breath_pack1. The locator makes it easier to see the location of the emitter, to select it, and to track its position. Next, I track the Locator/emitter group to the first woman, placing and keeping it just in front of her mouth like a carrot in front of a horse. Figure 2. Not to say this woman is a horse. I mean, I donít even know her. She seems nice and all. Actually sheís kind of cute, I wonder if sheís seeing anyone.

But I digress.

Ok, once the breath_pack has been tracked, I am ready to animate the rate of the particle emitter to correspond to her exhales. What I will be looking for here is not just when she exhales, but also how. Is she talking? Is she letting out a big sigh? Has she suddenly been hit by a shopping cart? This will dictate how much breath is being exhaled, which will directly correspond to how high the rate needs to be turned up.



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