Coordinate Systems for Unreal Engine Simulation in UAV Toolbox

UAV Toolbox enables you to simulate your UAV scenario in a virtual environment that uses the Unreal Engine^® from Epic Games^®.

Note

Simulating models in the 3D visualization environment requires Simulink^® 3D Animation™.

UAV Toolbox uses these coordinate systems to position objects in the Unreal Engine visualization environment.

Unreal Engine World Coordinate System

The simulation environment uses a right-handed Cartesian world coordinate system defined in ISO 8855[1]. In this coordinate system:

• When facing the positive X-axis, the positive Y-axis points to the left.

• The positive Z-axis points upward from the ground.

• Yaw, pitch, and roll angles have clockwise-positive directions when looking in the positive directions of the Z-, Y-, and X-axes, respectively.

Note

The Unreal Editor uses a left-handed world Cartesian coordinate system in which the positive Y-axis points right with respect to the positive X-axis. If you are converting from the Unreal Editor coordinate system to the coordinate system of the 3D environment, you must reverse the signs of the Y-axis, pitch angle, and yaw angle.

World coordinate system is fixed and centered on the Unreal Engine scene origin.

This figure illustrates how the Simulation 3D UAV Vehicle block uses this coordinate system to determine the UAV location and orientation in the US City Block scene. The Translation inputs specifies the position of each UAV relative to the scene origin, and the Rotation input specifies the orientation of the vehicle frame of each UAV relative to the world coordinate system.

Vehicle Coordinate System

The vehicle coordinate system is based on the world coordinate system and follows the ISO 8855. The coordinate system is fixed to the UAV. In this coordinate system:

• The X-axis points forward from the vehicle.

• The Y-axis points to the left of the vehicle.

• The Z-axis points up from the ground.

• Roll, pitch, and yaw are clockwise-positive when looking in the forward direction of the X-, Y-, and Z-axes, respectively.

UAV Toolbox uses the frame rotation angles between the world and vehicle frame in a ZYX (yaw-pitch-roll) rotation sequence to determine the orientation of the UAV.

This figure illustrates the vehicle coordinate system of a Quadrotor vehicle.

Sensor Coordinate System

You can add a sensor to your UAV scenario simulation as one of these blocks:

• Simulation 3D Camera

• Simulation 3D Lidar

• Simulation 3D Fisheye Camera

• Simulation 3D Ultrasonic Sensor

When you add a sensor to the scenario, you can choose to mount the sensor relative to the scene origin or the UAV origin by specifying its Mounting Location parameter. If you specify the parameter as scene origin, the sensor remains stationary during the simulation. If you specify the parameter as a vehicle name, then the sensor attaches to the specified UAV. In addition, you can specify the relative translation and rotation of the sensor with respect to the scene or vehicle origin by specifying the Relative translation [X, Y, Z] and Relative rotation [Roll, Pitch, Yaw] parameters, respectively.

By default, the sensor output, relative translation, and relative rotation are specified in ISO8855 coordinate system. However, you can choose a different coordinate system using the Coordinate system parameter of the sensor. This table illustrates the different coordinate systems you can choose for sensors:

Coordinate System	Block Parameter Option	Description
Unreal Editor coordinate system	Default	The Unreal Editor coordinate system is a left-handed Cartesian coordinate system, with units in meter and radians. Axes X-axis points away from the viewer. Y-axis points to the right. Z-axis points upward. Rotation Roll — Clockwise rotation about the X-axis. Pitch — Clockwise rotation about the Y-axis. Yaw — Counterclockwise rotation about the Z-axis.
MATLAB® coordinate system	MATLAB	The MATLAB coordinate system is a right-handed Cartesian coordinate system with Z-up orientation, with units in meter and radians. Axes X-axis points away from the viewer. Y-axis points to the left. Z-axis points upward. Rotation Roll — Clockwise rotation about the X-axis. Pitch — Clockwise rotation about the Y-axis. Yaw — Clockwise rotation about the Z-axis.
ISO 8855 standard coordinate system	ISO8855	The ISO 8855 standard coordinate system is a right-handed Cartesian coordinate system with Z-up orientation, with units in meter and radians. This coordinate system is defined in the ISO 8855 standard. Axes X-axis points away from the viewer. Y-axis points to the left. Z-axis points upward. Rotation Roll — Clockwise rotation about the X-axis. Pitch — Clockwise rotation about the Y-axis. Yaw — Clockwise rotation about the Z-axis.
X3D ISO standard coordinate system	VRML	The X3D ISO standard coordinate system is a right-handed Cartesian coordinate system with Y-up orientation, with units in meter and radians. Axes X-axis points away from the viewer. Y-axis points upward. Z-axis points to the right. Rotation Roll — Clockwise rotation about the X-axis. Pitch — Clockwise rotation about the Y-axis. Yaw — Clockwise rotation about the Z-axis.
SAE coordinate system	SAE or AERO	The SAE J670 [2] standard coordinate system is a right-handed Cartesian coordinate system with Z-down orientation, with units in meter and radians. This coordinate system is defined in the SAE J670 standard, and is used for aerospace applications. Axes X-axis points away from the viewer. Y-axis points to the right. Z-axis points downward. Rotation Roll — Clockwise rotation about the X-axis. Pitch — Clockwise rotation about the Y-axis. Yaw — Clockwise rotation about the Z-axis.

References

[1] Technical Committee. Road vehicles — Vehicle dynamics and road-holding ability — Vocabulary. ISO 8855:2011. Geneva, Switzerland: International Organization for Standardization, 2011.

[2] Vehicle Dynamics Standards Committee. Vehicle Dynamics Terminology. SAE J670. Warrendale, PA: Society of Automotive Engineers, 2008.