Requirements: Digital Fusion
Flow:  Flow. (4 K)
Images:  TGA. (650 K)
Archive:  Printable Microsoft Word Document. (560 K)

Sooner or later we all come across this one, we need to simulate some heat waves. Whether it is for a 3D animation, or just an early morning shoot where the road wasn't hot enough yet, you've got to add some visual distortion.

The process in this tip is quite simple. The real technique comes in analyzing the desired effect beforehand and getting as close to it as possible. I'm amazed at how often I get approached and asked "My (insert appropriate thing) doesn't look right…. Why?" The trick is to pour through reference footage and material. Anything you can get your hands on. Once you have a goal to work towards it becomes much easier to simulate it.

I've rendered a 3D jet and background, and wish to make it look hot. Specifically I wish to add the blurry waves of distortion coming from the jet exhaust. Sounds like the perfect job for a displacement tool, however we need to drive the displacement with an image. In this case I've chosen to go with a particle system. Digital Fusion's particle system offers the flexibility we need to vary the look of the distortion and tailor it to our needs.

1. Start off with a new flow, and load the footage of the plane.
2. Create the basic particle system, and position it near where the jet exhaust would be.
3. Change the emitter control settings as follows;
   1. Number=40
   2. Lifespan=30
   3. Velocity=0.1
   4. Velocity Variance=0.03
   5. Angle=5
   6. Angle Variance=28
   7. Angle Z Variance=45
   8. Rotation Z=90
   9. Rotation Z Variance=45

4. Change the emitter style settings as follows;
   1. Style=Line
   2. Color Variance R,G,B, = low -0.2 high 0
   3. Scale over life to approx. 1.5 on death
   4. Fade out at 0.8

5. Set the following under the controls for the Prender tool;
   1. Blur=3
   2. Pre-Generate frames=30
   3. Automatic Pre-roll=Yes

6. Enter these settings under the scene tab;
   1. Y rotation =60

From here, if you create a preview, you should see a fairly believable heat wave near the jet. I chose the line type of particle, and rotated it 90 degrees to help achieve the look of waves moving through the air. I also used the 3D capabilities of the particle system to help simulate the camera looking into the scene, rather than a stuck on 2D effect. Unfortunately, the current flow is also deforming the jet. To fix this we will use a bitmap mask to limit the effect of the distortion.

7. Add a second loader to your flow, and point it to the mask image.
8. Right click on the displace view, and choose "effects mask/bitmap"
9. Drag and drop the second loader (of the mask) to the appropriate area on the mask.
10. Invert the mask.

Create a preview at this point. Things are looking pretty good. If you want to add the final touch to the scene, try adding the darker exhaust smoke from the jet.