6.7.1 Proximity alerts

There can be a high volume of sensor tracks near friendly units prior to and during battle; it would overwhelm the user to see an alert on every change to every track. We keep a threat envelope for each friendly unit, consisting of tracks close enough to pose a threat to it. Tracks are placed in zero or more threat envelopes when they appear or move. Only significant changes to the strength of the aggregate force in an envelope or the closeness of the nearest track causes an alert.