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When you change a parameter that affects a planar tracker, any prior tracking results no longer correspond to the current settings. For example, if you move a corner location slightly on a key frame, this will change the tracker reference position and likely tracker location on all frames that have been tracked using this frame as a reference.
Just about every parameter change ripples from one frame to the next throughout the shot in a version of the infamous "Butterfly Effect". (Tracking is inherently quite different than animation systems you are familiar with.)
So in theory, when one parameter changes, we should invalidate many or all already-tracked frames, marking them for re-tracking.
In practice, that can cause a lot of unnecessary work.
It's far more convenient to allow you to change parameters without necessarily erasing everything else immediately. Many minor changes wind up not really mattering, at least immediately. By not immediately invalidating earlier work, you can proceed through a shot. This is especially important with changes in tracking direction, etc.
Ultimately, you can wind up with a situation where the stored tracking data is not internally self consistent, as it was created with one set of parameters in one area, and a different set in another area.
We recommend that if you've been busy experimenting with parameters over the course of a track, you go back and have it re-track through once more without making changes to ensure that everything is self consistent (eliminating path glitches due to such changes).
©2023 Boris FX, Inc. — UNOFFICIAL — Converted from original PDF.