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Travel of Cam/Obj . Scale the scene so that the camera or object has moved the given distance between the two frames, for example, the length of a dolly track.
(This section jumps way ahead to discuss joint camera and object shots. It's discussed there too, and is well worth reading twice, or more.)
When both the camera and object are moving, it is important to control the scale of both the camera and object. The shot images themselves may not provide sufficient information to do this, which is the basis of an optical illusion commonly used for the optical effect behind movies such as "Honey, I Shrunk the Kids." When on-set measurements are used, both the set and the moving object must be measured. That doesn't always happen.
Some particular situations in these shots can be used to set the relative sizing correctly. Essentially, these situations are ones that are "tells" — that give away the optical illusion. When these situations arise, special phases can be used to adjust the relative scaling correctly.
Moving-Object Path. The special situation is that the moving object comes to a stop for some portion of the shot, which the camera continues moving in a sufficiently complex manner. Or, the moving object may follow a precisely straight line for some portion of time. In either case, the phase experimentally modifies the relative scaling until the desired objective—a complete stop or straight line—is obtained.
Moving-Object Position. Here, the special situation is that some trackers on the moving object come close to, or into alignment with, some trackers on the camera, or at least with the coordinate system. For example: a thrown object is tracked as it flies across the room, coming to rest on the ground plane. The scale of the object is adjusted so that if lies on the ground plane at the end of the shot.
These phases provide a powerful tool for accurately and automatically setting the relative coordinate scaling when the relevant situations occur.
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