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Preparing Trackers for Holds
It is crucial to maintain a smooth 3-D path in and out of a hold region—you do not want a big jump. To achieve this requires careful control over whether trackers are far or
not. The operations and discussions that follow rely heavily on the
graph editor’s tracks
view
of the world.
To begin with, a tracker must be configured as Far if the camera does not translate within its lifetime (ie the tracker’s lifetime is contained within a hold region). A tracker with a lifetime solely outside the hold region will generally not be far (unless it is in fact far, such as a point out on the horizon).
Trackers that exist both inside and outside the hold region present some more interesting questions, yet they are common, since the auto-tracker rightfully does not care about the camera motion—it is only concerned with tracking image features.
If non-far trackers continue into a hold region, they will inevitably cause the best XYZ position of the hold region to separate from the last XYZ position before the start of the hold region. The additional tracking information will not exactly match the prior data, and frequently the hold region contains a rapid pan that tends to bias the tracking data (including a rolling shutter in the camera). A jump in the path will result.
To prevent this, SynthEyes only pays attention to non-far trackers during a short transition region (see the Transition Frms. setting on the Solver panel ). Inside the transitions at each end of a hold region, non-Far trackers are ignored; their weight is zero to the solve. This ensures that the path is smooth in and out of the hold region.
This causes an apparent problem: if you take an auto-tracked shot, turn on the hold button, then inside the hold region, there will be no operating trackers (and the Lifetimes panel will show those frames as reddish). There are no far trackers, and no usable tracks in there! Your first instinct may be that SynthEyes should treat the trackers as normal outside the hold region, and as far inside the hold region—an instinct that is simple, understandable, and mathematically impossible.
It turns out that the non-far and far versions of a tracker must be solved for separately, and that the sensible approach is to split trackers cleverly into two portions: a non-far portion, and one or more far portions. The lifetimes of the trackers are manipulated to smoothly transition in and out of the hold region, and smooth paths result.
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