Tracking Scaling

In this case, you want the object to remain stationary and track only changes in scale. For example, assume that a camera is looking down a straight road at a car approaching. You need to track the license plate as the car approaches. Note that in this example there are no rotation or position changes.

The Tracker requires two tracker boxes to measure scaling. The changing distance between the centers of the two reference boxes determines the scale.

In the license plate example above, you want to "lock" a new license plate to the old one. You would position one reference box over one corner of the license plate and the other reference box over the diagonally opposite corner.

In this example, the license plate is a layer. It assumes you have a composite operator with two layers—the source layer and the target layer. (In this example, the source is the car clip and the target is the license plate clip.) See Creating Composites.

To track changes in scale only:

1. Determine a good reference frame and position the source clip at that frame. Position the target object as required.
2. Select the target object (the object you want to have follow the scale changes).
3. On the Tracker panel, select the source layer (in this example, the car) from the Source list.
4. Click Scale.

Two Trackers appear. The first Tracker is over the pivot point of the object and the second appears to its lower right.

5. Resize and reposition each Tracker so that they track the scaling change. (In this example, the Trackers are placed over the upper right and lower left corners of the license plate.)
6. Adjust the settings for each Tracker as necessary.
7. On the Tracker panel, click Select All Trackers.
8. Click one of the Analyze controls to start the analysis.

The Trackers follow the reference features, and the target object is scaled accordingly.

9. If you encounter difficulties, pause the analysis, make adjustments, and restart the analysis as necessary. See Advanced Tracking Techniques.
10. Export the Tracker data if necessary.
11. Click the Off button in the Tracker panel when tracking is complete.