Tracker motion files are ones which contain markers with only position data. These file are created by optical motion capture systems as the first result from the motion capture session. Further processing is required to generate skeletal from these marker files. The optical motion systems are typically broken up into two categories: full body motion capture and facial motion capture. Facial motion capture is usually done with a single camera tracking very small markers places on a performers face. Full body motion capture is done with multiple cameras, usually 6-8 cameras but sometimes as many as 12, and larger markers are placed on the body.
With a single camera the data is returned as 2-D data, full body motion capture returns 3-D data. By adding a zero third dimension to the facial data the same file formats can be used to represent both kinds of data sets.