The Tracker is a tool for following and capturing the motion of an on-screen feature, and then applying that stored motion to a second element, so that the two appear to be locked together.
You can track any number of features in a length of footage:
1-point tracking Tracks a single feature for position.
2-point tracking Tracks two features, using the relationship between the two to track scale/rotation.
4-point tracking Tracks four features, also referred to as corner pinning.
Multiple-point tracking Tracks as many features as you want.
You can apply the stored motion to various elements:
Center point of an object For example, you could track a halo over the head of a person in a clip. Assume that in the clip a woman tilts her head and advances toward the camera. You would want the halo to reflect the position, scaling, and rotational changes of the tracked features on the woman's head.
When you track scaling, you are not performing 3D tracking in true Z-space. You are simply measuring the amount of change over time in the size of the tracked object.
Control points of an object The shape of the object changes to reflect the motion of the reference feature its control points are locked to. For example, if you want to replace the label on an actor's clothing, each corner on the new label would track a corner on the old label. The shape of the new label would change to correspond to those movements.
