Modeling & Simulation > E6DOF Trajectory Generator

E6DOF - An Easy to Use Dynamic Trajectory Generator

The E6DOF waypoint trajectory generator, developed by Network Sensing Technologies (NST), is a generic point mass 6-Degee-of-Freedom flight path trajectory generator. It generates a trajectory that passes through a sequence of user defined waypoints referenced to the World Geodetic System 1984 (WGS-84) ellipsoid

E6DOF is a 64-bit C#/C++ software application that executes on Windows 10 platforms. E6DOF GUI creates scenarios which are saved in XML format. E6DOF parses the XML input file that contains airframe maneuverability parameters, initial conditions, and a sequence of waypoints. E6DOF’s output is a time history ASCII output file containing the trajectory data. It can be invoked via command line with corresponding .XML input file. NST has various fidelities of 6DOF models based on the E6DOF that includes GPS/INS error models which are used for different purposes and applications. This version's outputs are uncorrupted by GPS/INS error modeling.

E6DOF implements a six degree-of-freedom simulation of an airborne platform. Originally developed as a medium fidelity model for GPS/INS guidance / transfer alignment studies, it was extended to provide a software component in real-time closed loop operations with GPS RF simulators and GPS UE. Later the E6DOF received modification for hardware in the loop stimulus to GPS and other RF stimulators as well as Embedded GPS Inertial navigators for open loop deterministic testing. The E6DOF Capabilities are simplified to support streamlined testing without the extra burden of GPS/INS error models, Kalman filters etc. E6DOFs simulated platform is generic, without an aerodynamic model. Maneuver parameters limiting accelerations and angles-of-attack are specified by input parameters. Initial conditions and a sequence of waypoints describe the desired trajectory. Two autopilot types are supported: Bank-to-Turn (BTT) and Skid-to-Turn (STT). BTT autopilots are typically used on aircraft. This autopilot will cause the platform to roll and pull Gs until the desired vertical acceleration vector is aligned with the next waypoint. Almost all accelerations sensed by the “pilot” are upward”. Downward accelerations are limited to 1 G and lateral accelerations are minimized. Skid-to-turn autopilots are typically used on projectiles and other high dynamic unmanned aerial vehicles. The STT autopilot will minimize the roll angle and pull significant accelerations in both the vertical and lateral directions. E6DOF implements two waypoint-based guidance laws (Time-at-Waypoint Guidance or Velocity-at-Waypoint Guidance) defined by latitude, longitude, altitude, and the type (Time or Velocity) parameter. The Time-at-Waypoint Guidance law uses an optimal controller to command a thrust that is designed to place the platform at the waypoint at the specified time. The Velocity-at-Waypoint Guidance law will try to maintain the commanded velocity between waypoints. E6DOF cannot generate trajectories for every conceivable sequence of waypoints as the guidance law in use vs waypoints spacing that may violate physics.

Defining E6DOF Trajectories

Methodology for waypoint based 6DOF trajectory generation is rather simple; specify the maneuverability parameters, initial conditions, waypoint laydown via mouse map entry or manual inputs, a pre-validation phase, modification if necessary and finally trajectory generation. The default step size interval is 5 msec. The same E6DOF model is used for Waypoint, Satellite and Ship based trajectories.

The Maneuverability Parameters section defines several fields that allow you to constrain the motion of the platform. The parameters are:

  • Maximum Vertical Acceleration: The maximum vertical acceleration in the body frame limited to 10.78 to 196 m/s2 (1.1 to 20 Gs).
  • Maximum Lateral Acceleration: The maximum lateral acceleration in the body frame limited to 10.78 to 196 m/s2 (1.1 to 20 Gs).
  • Maximum Thrust: The maximum axial thrust limited to 9.8 – 100 m/s2.
  • Maximum Velocity: N/A. For Ballistic trajectories.
  • Maximum Pitch Angle-of-Attack & Maximum Yaw Angle-of-Attack: Limited to 0.1 to 20 degrees
  • Maximum Roll Rate: Limited to 60 to 360 deg/sec.
  • Maximum Roll Rate: Limited to 60 to 360 deg/sec.
  • Autopilot Type: Select autopilot type: Bank-to-Turn or Skid-to-Turn
  • The Parameter Type allows guidance law selection for platform velocity control Two options are:

  • Velocity – The platform will command a thrust that generates the specified velocity before reaching a waypoint.
  • Time – The platform will use an optimal control law (Zero-effort miss) that generates the thrust needed to arrive at the waypoint at a user defined time.

    Waypoints may be entered either as Latitude, Longitude, Altitude or by clicking on the World Map

    It is possible to laydown waypoint trajectories with limited initial and maneuverability settings such that the waypoints cannot be reached causing an endless loop as the E6DOF attempts to fly through the waypoint, circling back over and over. The E6DOF Editor will not create a trajectory without first validating convergence with the constraints and waypoints selected.

    Trajectory File – Space Delimited:

    Column Parameter Units
    1 Time Seconds
    2 Longitude Degrees
    3 Latitude Degrees
    4 Altitude Meters Relative to WGS84
    5..7 ECEF Vel X,Y,Z Meters/Seconds
    8..10 ECEF Accel X,Y,Z Meters/Second2
    11.13 Roll, Pitch, Yaw (hdg) Degrees
    14..16 Body Rate X,Y,Z Radians/Second
    17..18 Angular Accel X,Y,Z Radians/Second2

    Trajectory Debug File – Space Delimited:

    Column Parameter Units
    1 Time Seconds
    2 Longitude Degrees
    3 Latitude Degrees
    4 Altitude Meters
    5..7 North, East, Up Velocity meters/second
    8..10 North, East, Acceleration meters/second2
    11..13 Roll, Pitch, Yaw Degrees
    14..16 Body Rates X,Y,Z degrees/second
    17..19 Angular Acceleration X,Y,Z degrees/second2
    20 Bearing degrees
    21 Dive Angle degrees
    22..23 Pitch & Yaw AOA degrees
    24..25 Pitch & Yaw AOA dot degrees/second
    26..28 Accel Body X,Y,Z meters/second2
    29 Dive dot degrees/second
    30 Bearing dot degrees/second
    31 Commanded Pitch AOA degrees
    32 Commanded Yaw AOA degrees
    33 Theta dot degrees/second
    34 Commanded Roll degrees
    35 Axial Thrust meters/second2
    36 Commanded Vertical Acceleration meters/second2
    37 Roll Error degrees
    38 Pitch Command degrees
    39 Yaw Command degrees
    40 Roll from Accel degrees
    41 Roll GuidanceMode na
    42 Acceleration Magnitude meters/second2
    43 Next_Index na
    44 Slant Range Meters
    45 Range Rate meters/second
    46 Vertical 1 = almost +/-90deg
    47 Roll Rate Cmd Deg/sec

    Note: Things Change Rapidly! Specifications, Capabilities, Features and Availability Subject to Change Without Notice and May Be Restricted to Certain Users.