Offset Tracking lets you use a different area of a shot for generating the track compared to the position of the shape itself. If a different area of the shot becomes the best candidate for generating the actual tracking data, we can use it by creating an offset shape and positioning it over this better area.
Enabling the Offset button will activate a copy of the tracking shape :
The copy is green. Initially, it is placed on top of the original shape.
We can switch to the Transform menu :
Then move the offset shape to our new preferred position :
Once in place, we can switch back to the Shape menu :
and continue our tracking.
The tracking data is calculated from the offset shape and applied to the original.
When the Offset button is enabled, the offset shape is used to generate the track. You can set the offset shape to any suitable position in the frame. If a better position becomes apparent, you can re-position it again.
For an offset shape track calculation to work properly, both the original and the offset shape need to share the same type of motion.