A track algorithm is a radar and sonar performance enhancement strategy. Tracking algorithms provide the ability to predict future position of multiple moving objects based on the history of the individual positions being reported by sensor systems.
Historical information is accumulated and used to predict future position for use with air traffic control, threat estimation, combat system doctrine, gun aiming, missile guidance, and torpedo delivery. Position data is accumulated over the span of a few minutes to a few weeks.
There are four common track algorithms. Nearest Neighbor Probabilistic Data Association Multiple Hypothesis Tracking Interactive Multiple Model (IMM)
History
The original tracking algorithms were built into custom hardware that became common during World War II. This includes storage tubes used with planned position indicator displays, range height indicator displays, and pen-plotting boards used for civilian air traffic control and waterway management. It also includes custom analog computers, like the Mark I Fire Control Computer used with radar data to aim guns, missiles, and torpedoes associated with military air traffic control and waterway management.
Track algorithms were migrated from analog equipment to digital computers from the 1950s through the 1980s. This was necessary to eliminate limitations that include mid-air collisions and other problems linked with obsolete equipment that was socialized by PATCO and United States Department of Defense. Similar migration trends occurred in other countries throughout the world for similar reasons.
Modern civilian air traffic and military combat systems depend upon a custom track algorithms used with real-time computing slaved to displays and peripherals.
Limitation for modern digital computing systems are processing speed, input-output throughput rate, the number of input-output devices, and software compatibility with upgrade parts.
Terminology
Tracking algorithms operate with a cartesian coordinate system. This is often called a rectangular coordinates, and is based on north–south, east–west, and altitude. Sensors operate using a polar coordinate system. This is often called spherical coordinates based on elevation, bearing, and range. Some common terminology is as follows.
Human Interface
Users are generally presented with several displays that show information from track data and raw detected signals.
Plan position indicator
Scrolling notifications for new tracks, split tracks, and join tracks
Range amplitude display
Range height indicator
Angle error display
Audible alerts (buzzer or voice)
The audible alert draws attention to the scrolling notification. This will present the track number for things like separation violation (impending collision) and lost track not located near a landing facility.
The scrolling notifications and audible alerts require no user action. Other displays activate to show additional information only when a track is selected by the user. The primary human interface for the tracking algorithm is a planned position indicator display. This typically puts up four pieces of information.
The track algorithm produces symbology that is displayed on the Plan Position Indicator.
Users have a pointing device with several buttons that provides access to the track file through the Plan Position Indicator. The typical pointing device is a track ball, which operates as follows.
Hook action turns off the cursor and displays additional information from the track algorithm. The user can perform actions while the hook is active, such as communicate with the vehicle or notify other users regarding the vehicle associated with the track.
Operation
The nearest neighbor track algorithm is described here for simplicity.
Each new detection reported from incoming sensor data is fed into the track algorithm, which is used to drive displays.
Track algorithm operation depends upon a track file, which contains historical track data, and a computer program that periodically updates the track file.
Sensors information (radar, sonar, and transponder data) is provided to the track algorithm using a polar coordinate system, and this is converted to cartesian coordinate system for the track algorithm. The polar to Cartesian conversion uses navigation data for sensors mounted on vehicles, which eliminates sensor position changes caused by ship and aircraft motion that would otherwise corrupt track data.
Track mode begins when a sensor produces a sustained detection in a specific volume of space.