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:

- Determining which items from the two lists are to be associated.
- 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.*

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:

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

*
*

Wed Mar 1 10:19:35 EST 1995