Apple Motion 4 - Manual (Page 1296)

A second strategy is to lower the Fail Tolerance value. With a lower Fail Tolerance value,
the tracker is more likely to find a false match. With a higher value, the tracker is more
strict in finding a match. Click the track’s disclosure triangle to display the Fail Tolerance
parameter.
Another strategy is to jump to the midpoint frame of the clip and track forward to the
end frame of the clip. Then return to the midpoint frame and track backward to the
beginning of the clip.
Tracking Obscured or Off-Frame Points
In addition to experimenting with different tracker parameter settings, there is a basic
technique to correct track points that are obscured by moving offscreen or by an object
passing in front of them.
The following sequence is a simple example of a candidate for offset tracking. As the car
moves forward, it passes a tree that temporarily obstructs the reference pattern.
When the reference pattern becomes obscured, the Offset Track checkbox lets you move
the tracker, picking a new reference pattern in a different area from the original reference
pattern. The offset between the original reference pattern and the new pattern is calculated
to maintain continuity in the resulting track path.
In the following example, the track is obscured by a tree, so the tracker is moved to a
nearby reference pattern, and tracking continues until the original pattern reappears.
Even though one region is examined, the points are saved in another region. The second
tracking pattern should travel in the same direction as your original pattern.
To offset (move) the onscreen tracker control to an unobstructed area of the image
1 Go to the frame where you want to begin the offset track.
1296 Chapter 19 Motion Tracking