Unit and Coordinate Conventions
- 1 Overview
- 2 Units
- 3 Coordinates
- 3.1 World space
- 3.2 Local space
- 3.3 Rotation
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.
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