Two-dimensional Report Formation

The report formation subtask of the two-dimensional tracker collects/organizes established two-dimensional tracks into a list to be used as input for three-dimensional track initiations, where ``established'' simply means tracks older than some minimum cutoff age (typically seven hits). The task of initiating three-dimensional tracks from lists of two-dimensional tracks consists of two parts:

1. Determining which items from the two lists are to be associated.
2. Constructing three-dimensional state information for associated pairs.

The essential element in associations is the so-called hinge angle illustrated in Figure 18.19. Consider a single target viewed simultaneously by two different sensors. Assuming that each two-dimensional tracker knows the orbits of the other tracker's sensor, each tracker can independently reconstruct two reference planes in three-dimensional inertial space:

SSE:

The plane containing the two sensors and the center of the earth.

SST:

The plane containing the two sensors and the target.

The hinge angle

 

is simply the angle between these two planes.

  
Figure 18.19: Definition of the Stereo Association Angle

Once the time for the two-dimensional report has been specified, the steps involved in the report function are relatively straightforward:

1. Select all tracks satisfying the minimum age requirement.
2. Use the state model in Equation 18.6 to propagate these tracks to the reference time
3. Evaluate both and its time derivative at the reference time
4. Sort the list of reported tracks by values.

The state model in Equation 18.6 not only provides the mechanism for synchronizing the report items but also the additional variable , which ultimately aids in the associations of report lists from two two-dimensional systems.