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Tracking Direction
You'll track starting from the frame on which the model is aligned. If that's the first frame of the shot, great, you can track forward to the end. If the model is aligned on the last frame, you'll track backwards through the shot to the beginning.
If the model is aligned somewhere in the middle of the shot, you'll track through to the end, then click back to the middle of the shot, change the tracking direction, and track from the middle to the beginning. (Alternatively you can track from middle to beginning, then middle to end; it doesn't matter.)
In an animation package, playback direction doesn't matter much; the animation curves are already all planned out and don't depend on direction. In tracking, the direction matters a lot because the curves are not already generated: they are being determined as you go along, based on earlier reference frames. Which direction is "earlier" matters hugely, especially as you work on a shot for a while. When you change the GeoH tracking direction, a fair amount of work takes place to adjust the joint locks of every GeoH object in the scene.
To track in a specific direction, you need to have the tracking direction arrow at top left of the GeoH panel and the playback direction arrow so that they are both pointing in the desired direction.
All GeoH trackers in the scene, selected or not, are affected by the GeoH direction control (unlike regular trackers). It would be too confusing to have a parent tracking in one direction, and various children in another.
Tracking occurs when you "Play" the shot, or step through it using the frame forward or frame back arrows (as appropriate), or when you spin the middle-mouse scroll wheel in the perspective view (as long as the perspective view is locked to the shot imagery, and not zoomed into it).
Important : All GeoH object tracking occurs only on the current frame, even if it is seemingly trivial. So if you change the hierarchy or various other controls, the object paths aren't affected until you actually track through the shot (via Play) so that all frames are re-tracked.
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