The algorithm described in Section 18.4.4 is only applicable for extending tracks which already exist in the track file. The creation of new entries is done by a separate track initiation function.
The track initiator involves little more than searches for nearly colinear triples of data over the last three scans. A triplet
:
:
:
where the cutoff is generally fairly loose (e.g., 
). In
addition, a number of simple heuristic cuts (maximum speed) are applied.
The initiator searches for all approximately linear triples over the last
three scans, subject to the important additional restriction that no
initiations to a particular item 
of the current data set are
attempted if any established track (minimum age cut) already exists
ending at that datum. The nominal 
complexity of the initiator is
reduced to approximately 
by exploiting the sorted dature on
the incoming data sets.