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Tracking Forwards or Backwards
Each tracker in SynthEyes (planar or regular) has a tracking direction, shown by the small arrow underneath the tracker mini-view. This tracker direction is different than the playback direction arrow on the main timebar; either can be changed at any time.
When you hit Play on the main time bar, only trackers with the same direction are updated, ie tracked to follow whatever they are following. Trackers with a different direction are shown, but only show previously-obtained results.
Though this may seem unnecessary at first glance, it turns out to be essential to providing the experience you expect otherwise. (Tracking is more like simulation than animation; it is causal with one thing depending on the next ... time flows in a particular direction.)
When you create a tracker, it takes its direction from the current play direction.
You can hit Play, and it will track through the shot (along with any other unlocked trackers in the same direction setting).
If you needed to create the main frame somewhere in the middle of the shot, you can then go back to the main frame and click the tracker's direction arrow, to change the direction of the tracker. SynthEyes will make some updates to the tracker's enable track (and for regular trackers, add some position keys) to accommodate the changed tracking direction.
The main playback direction will also change, for your convenience, and you can then click Play to continue tracking in the new direction.
You can change a tracker's direction as often as necessary, with different frames tracked in different directions. This can cause some subtle issues, however.
When planar tracking, SynthEyes uses as a reference the most recent key... ie the closest keyed frame behind the current frame, considering the tracker's tracking direction. If there are multiple keyed frames, the reference frame for a specific frame depends on the tracking direction. With keys at frame 20 and 30, the reference is 20 when tracking forward, and 30 for tracking backwards.
If you change direction and retrack the same frame, you may get a different result, and neither one is specifically "right." In practice, this is rarely a significant concern; we point it out for your awareness, and present a little advice.
We advise not changing tracking direction too wildly or unnecessarily; have a little bit of a plan. If you do find that you have changed tracking direction repeatedly in a disorganized fashion, we advise doing a final tracking pass at the end that makes a single pass, or two with the main frame in the middle, to make all the tracking results consistent. That will prevent unexpected results if you update the track days or weeks later. It can be helpful to set a few more keys in problematic areas to ensure that the retrack stays on course.
©2023 Boris FX, Inc. — UNOFFICIAL — Converted from original PDF.