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Producing 2-D Trackers
Most commonly, you’ll produce a regular SynthEyes supervised tracker for each AprilTag, as selected by “Center Trackers” mode. Each tracker will be named something like Tag8 or Cam01Tag8, indicating both the tag data code and, if the Prefix name with camera checkbox is checked, the camera it was found on (so that trackers have distinct names in scenes with multiple cameras).
You can examine the tracking of each produced AprilTag tracker, and because it is a regular SynthEyes tracker, you can edit the tracking to fix any glitches such as small occlusions, or extend the tag’s tracking if the AprilTags tracker did not detect it,
even though it was still partially visible. If you’ve chosen even-width tags with a corner in the middle, you can examine and modify the trackers particularly well.
Tip : You can examine the Figure of Merit (FOM) channel for AprilTags- produced trackers in the Graph Editor, to evaluate trackers and to also help adjust the Contrast Quality setting. A higher FOM number is better!
With one tracker per AprilTag, you’ll still need enough visible AprilTags and regular trackers to be able to 3-D solve the scene. If the AprilTags are reasonably large, you can select the “Corner Trackers” mode of the AprilTags Detector. As the name suggests, it will put a tracker at each corner of the AprilTags square, giving 4 trackers per AprilTag, or even 5 if you select “Center and Corners”. Because those 4 or 5 trackers are on the plane and close together, they are correlated, containing less 3-D information than independent trackers would.
If you have three large, well separated, AprilTags where no two of them are co-planar, you may be able to use the Corner Trackers mode to get a 3-D solve with no additional trackers.
With some combination of AprilTags trackers and other auto-trackers and/or supervised trackers, you can then solve the scene. If this is a reference shot, you’ll align the scene in your desired fashion, and use the 3-D tag locations to align other shots (more discussion later). If this is a follow-on shot, you’ll use the previously-determined
3-D locations of the tags to align this shot to match the initial reference.
Important: Don’t try to use four corners from a single AprilTag to define a coordinate system unless the tag is very large! In typical shots, the corners are quite close together and can’t accurately constrain the coordinate system orientation (simple physics of measurement).
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