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Offset Tracking
In offset tracking, you track one feature in order to track another. Offset tracking utilizes additional controls on the tracker control panel to handle three situations:
- the feature being tracked is temporarily obscured, but a nearby feature is not,
- overlaying a correcting animation on top of an existing tracker that has a slow drift, and
- when an additional feature is to be tracked that is very close to an existing completed tracker.
When handling obscured features, hand-animated tracking can be simpler for shots where the camera is mounted on a crane or dolly. Offset tracking is valuable for shots from hand-held cameras, since the already-tracked vibration carries over automatically to the offset tracker.
In the cases above, you'll use the
Tracker control panel's
offset channels, which offset the final tracker position from the position being visually tracked. The offset is applied only if the Offset button is turned on. You can animate both the offset enable button and the offset channels, though usually you'll create the offset values by dragging in the camera view, rather than adjusting the spinner values.
WARNING : you should have plenty of experience with supervised tracking before considering offset tracking. The offset trackers can only be as good as the original supervised tracks.
When the offset is enabled, you'll see a small crosshair at the final location, and the usual tracking graphics at the location being visually tracked as long as the tracker is not locked. If the tracker is locked, then the tracker graphics are the standard locked-tracker graphics, at the final location.
Similarly, the tracker mini-view and SimulTrack views show the location being visually tracked if the tracker is not locked, and show the image of the final location if the tracker is locked.
Important : Offset tracking is always less accurate than tracking real image features: you're making data up, hopefully artfully, so it's only an approximation to the right position. Temporarily disabling the tracker may be a better alternative. Offset tracking is valuable when very few trackable features are available, or when unaddressed lens distortion or other tracking issues are causing pops when trackers appear or disappear (see also the Transition Frms. spinner on the Solver panel).
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