Overview

These are the conventions used by Autonomy.

Units

All units are in SI.

Angles are in radians.

Coordinates

World space

AKA global or absolute.

WGS 84 :

• Axes: Latitude [decimal degrees], longitude [decimal degrees], altitude [metres]

  • Increasing altitude is moving away from centre of the Earth

• Origin: Equator, IERS reference meridian (IRM) (prime meridian), mean sea level

https://en.wikipedia.org/wiki/World_Geodetic_System

Local space

North east down (NED):

• Axes (Euclidean): North [metres], east [metres], down [metres]

  • Increasing value of down is moving towards centre of the Earth

• Origin (usually takeoff point): Latitude of home position, longitude of home position, altitude of home position (e.g. the ground)

https://en.wikipedia.org/wiki/Local_tangent_plane_coordinates

Rotation

The coordinate axes follow the right hand rule. When the axis is pointing towards you and axes are fixed, the angle increases in the counterclockwise direction.

The origin of the axes (i.e. 0 rotation) is specified in code as a comment. For example: The origin is the drone, so the camera gimbal rotates relative to the drone’s axes.