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18.4.5 Three-dimensional Tracking

Unlike the two-dimensional tracking module, the three-dimensional stereo tracker attempts to construct a single track for each (perceived) underlying target. The fundamental algorithm element for this type of tracking is the optimal associator described in Section 18.4.2. A single pass through the three-dimensional tracker utilizes optimal associations for two distinct subtasks:

Track extensions
Data from a sensor are associated with predicted data positions for existing three-dimensional tracks. This task is performed twice per scan, once for each two-dimensional subsystem of Figure 18.17.
Track initiation
Two-dimensional report lists are associated and new three-dimensional tracks are initiated for correlations to data points not used in the preceding track extension step.

As was noted in Section 18.4.2, a canonical problem with optimal associators is the possibility of globally poor associations due to incompatible lists or poor distance information for some of the entries in either lists. These problems are addressed as follows:
  1. Evaluations of individual distances for the cost matrix include relatively restrictive cuts which prohibit poor associations. The nominal cost for such associations is set to an ``infinite'' token and the association is simply ignored if selected in the course of minimization of Equation 18.5.
  2. Additional ``quality control'' modules are used to assess feasibility of proposed associations; tracks failing the quality constraints are deleted from the system.
The associators for track extensions and initiations and the quality control modules are described in the following subsections.

Guy Robinson
Wed Mar 1 10:19:35 EST 1995