Unit and Coordinate Conventions

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: World Geodetic System

Axis

Origin

Axis

Origin

Latitude [decimal degrees]

Equator, north is positive

Longitude [decimal degrees]

IERS reference meridian (IRM) (prime meridian), east is positive

Altitude [metres]

Mean sea level, away from centre of Earth is positive

World space relative altitude

AKA global relative altitude.

WGS 84: World Geodetic System

Axis

Origin

Axis

Origin

Latitude [decimal degrees]

Equator, north is positive

Longitude [decimal degrees]

IERS reference meridian (IRM) (prime meridian), east is positive

Relative altitude [metres]

Home position, away from centre of Earth is positive

Local space

North east down (NED): Local tangent plane coordinates

Axis (Euclidean)

Origin

Axis (Euclidean)

Origin

North [metres]

Home position, north is positive

East [metres]

Home position, east is positive

Down [metres]

Home position, towards centre of Earth is positive

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.