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The "Affect Parent" Setting
Normally, SynthEyes starts GeoH tracking at each root object. Once the root object has been tracked, it moves to the child GeoH objects, tracking each child and then its children. For example, on a full-body track, it tracks the torso, then moves to the upper arms and thighs, and down to the forearms and calves, then to the hands and feet (perhaps finally to fingers and toes). Once a given object is tracked, the tracking of the child objects does not affect the parent. And normally that's a good idea.
However, sometimes the child can supply information that isn't available solely from tracking the parent. Sometime the parent object may not be trackable at all!
For example, consider tracking the head of someone sitting calmly in a chair behind a tall-ish desk. We can start the GeoH hierarchy at the chair, at the base of the person's spine. Now we track the person's head! Even though we don't necessarily track the torso (largely behind the desk), this is a useful setup, because we constrain the possible locations of the person's head: their head won't suddenly jump a foot vertically (unless they are a small child no longer sitting in the chair). The position of the head indirectly constrains the configuration of the GeoH joints associated with the torso.
If we were to always track everything in strict order, that would be impossible, since there would be no way to generate a track for the torso before the head.
Instead, we take advantage of the "Affect Parent" setting for the head and intervening joints. When SynthEyes goes to track the torso, it examines the Affect Parent setting of its children, and their children, accumulating all the descendents that have the Affect Parent setting turned on. Then it tracks them (their unlocked joints) all at once. (The more joints being tracked at once, the longer it will take.)
Thus, the Affect Parent setting means that quite literally. Tracking the child can and should affect the tracking of the parent, so don't track the parent without tracking the child simultaneously.
Important & Warning : Affect Parent is an animated channel, so make sure that you turn it on for the desired range of times. You should animate it off when the object becomes obstructed or otherwise unusable, so that it does not affect the parent object.
This mechanism gives great flexibility, since objects may have even no unlocked joints—they can be used just for repositioning, or to get the desired ordering of joint rotations. The intermediate objects can be combined and tracked together, using Affect Parent. You should be alert for its use when the parent object cannot be tracked well, because of limited visibility or because the parent object offers only limited constraints on its own possible locations.
You might have to think a little and understand these geometric fundamentals to decide when you need to turn on Affect Parent. Normally, it should not be needed, and it should not be turned on unless necessary.
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