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im_sample_algorithm

MITRE's Interval Management Sample Algorithm. An implementation of RTCA DO-361A Appendix C.

State Data for Ownship & Traffic

As discussed in the entry points document, the code provides an Update method in IMAlgorithm.h that is used to call the algorithm repeatedly.

virtual Guidance Update(const Guidance &prevguidance,
                        const DynamicsState &dynamicsstate,
                        const AircraftState &owntruthstate,
                        const AircraftState &targettruthstate,
                        const vector<AircraftState> &targethistory);

Ownship State Definition

The ownship data (owntruthstate in the Update method above) is not expected to conform to ADS-B source definitions. The code provides a container class in AircraftState that defines the data elements needed for the IM Sample Algorithm to work correctly. The data elements of significance are:

Ownship ID (an integer uniquely identifying ownship’s aircraft source)
Simulation Time for this state (time of applicability)
Position (3 dimensional: x, y, z)
Ground Velocity (3 dimensional: x, y, z)
Sensed Wind Velocity (2 dimensional: x, y)
Sensed Outside Air Temperature

Traffic State Definition

The IM Sample Algorithm must be provided with traffic data at each update step (targettruthstate in the Update method above). The traffic data is not defined according to any “raw” definition of ADS-B data. However, it is reasonably derived from the information contained in an ADS-B traffic message. The code provides a container class in AircraftState that defines the data elements needed for the IM Sample Algorithm to work. The data elements of significance are:

Traffic ID (an integer uniquely identifing this state’s source aircraft)
Simulation Time (for this state, analagous to time of applicability)
ENU Position (3 dimensional: x, y, z)
ENU Ground Velocity (3 dimensional: xd, yd, zd)

IM Sample Algorithm Data Frequency

The IM Sample Algorithm is a control law designed to run at a nominal frequency of 1 Hz. However, that is not a strict requirement. The MITRE Corporation’s own research activities have successfully used this algorithm in a variable-frequency environment with no observed ill behavior. However, deviation from a nominal 1 Hz update rate is not recommended.

Using ADS-B Source Data for Traffic

There is no code provided to handle binary ADS-B source data. Use of such data will require custom development to translate that data souce into the state data definition described above for Traffic.