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The manner in which the elements of the preceding section are combined into
an overall tracking algorithm is governed by two fundamental assumptions:
- For substantial fractions of the scenarios under consideration,
the actual trajectories of the targets of interest are not fully constrained.
- The densities of targets are not so large as to preclude the
separation of individual targets over some/most of the time interval in
question.
The first assumption requires stereo tracking. Target motion along the
line of sight from any one sensor is assumed to be sufficiently ``unknowable''
that cooperative tracking from pairs of sensors is required to determine the
full three-dimensional state of a target. The second assumption is, in essence, a statement
of limitations of the entire Sim89 approach. The Sim89 tracker is ultimately
a point tracker in the sense that the algorithm attempts to associate
targets with individual data points provided by the sensors. This approach
makes sense only if the sensor can actually resolve individual targets for
most/much of the time. If the nature of the sensor and underlying targets is
such that a cluster of real targets is seen only as an ill-defined `clump' by
the sensor, the overall Sim89 prescription is inappropriate, and more
imaginative solutions to the tracking problem (e.g., track density estimation
by neural network techniques) would be required.
Given these assumptions on the nature of the tracking problem, the
overall form of the Sim89 tracking model is as illustrated in
Figure 18.17. The basic elements are a pair of
two-dimensional trackers, each receiving and processing data from its
own sensor, a three-dimensional tracking module which combines
information from the two two-dimensional systems, and a `Handover'
module. The handover module controls both the manner in which the
three-dimensional tracker sends its answers to whomever is listening
and the way in which tracks from other systems are entered into the
existing three-dimensional track files. The following subsections
provide brief descriptions of the algorithms used in each of these
component subtasks.
Figure 18.17: Gross Structure of Sim89 Tracking Model
Next: 18.4.4 Two-dimensional Mono Tracking
Up: 18.4 Multitarget Tracking
Previous: Multitarget Tracking
Guy Robinson
Wed Mar 1 10:19:35 EST 1995