The "Relative Object Position" Problem

This is the other important concept to keep in mind when Tweening. Remember, a Tween represents the average movement of all the objects (and the active camera) on the set. In this case, we started with the car flat on the ground in A, and ended with it airborne in B. As requested, the Tween depicts the car exactly as it would appear halfway between A and B--that is, halfway into flight even though the car has not yet reached the ramp.

Let me point out that a similar problem would occur if you Tween between B and C: rather than dropping nose-down first and then landing, the car would come down on its back end first.

But if you look closely, you'll see that there's another aspect to this problem to consider, too. Let’s zoom in on the car in our Tween to see what it is:

FIG VIII: arm in door

What’s happening here? Again, it’s a matter of averages. In Key Frame A, our driver has both hands on the steering wheel and her eyes forward like a good citizen of the road. In Key Frame B, on the other hand, she’s looking at the camera and raising a triumphant arm outside the window. Therefore, when we create a single Tween between those Key Frames, the driver is going to assume a pose halfway between A and B--which in this case puts her arm right through the door. Given that she’s not meant to be a cyborg, that’s not desirable.

So how do you get around this?

Again, by creating more Key Frames--as many as it takes to achieve the desired result. In the case of this entire car-jump-triumphant-driver shot, that means a total of six Key Frames:

1. Car enters shot on right (driver’s eyes forward and hands on steering wheel).

2. Car reaches bottom of ramp (driver’s eyes forward and hands on steering wheel).

3. Car climbs ramp (driver’s eyes forward and hands on steering wheel).

4. Car flies off top of ramp (driver’s eyes forward and hands on steering wheel).

5. Car lands in desired position (driver’s eyes forward and hands on steering wheel).

6. Car exits shot on left (driver’s head turned, smile on face, arm raised outside window in triumph).

Here’s how that looks:

FIG IX: 6 Key Frames

Note that these are all Key Frames; none are Tweens. They actually show the shot progression quite clearly--but they wouldn’t make a very smooth animation. For that, you need to create Tweens throughout the entire shot. The more tweens, the smoother the animation.

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