Compass stack

This collection of packages provides support for working with azimuths in ROS.

Packages

• compass_msgs: The message definitions.
• compass_conversions: Helpers for converting between different representations of azimuths.
• magnetic_model: ROS bindings for World Magnetic Model.
• magnetometer_compass: Support and ROS nodes for extracting azimuths from 3-axis magnetometers.
• magnetometer_pipeline: Calibration and removing of magnetometer bias.

Definitions

ENU frame is the standard orientation used in ROS. The abbreviation means East-North-Up and corresponds to the meaning of vector components X, Y and Z. A zero azimuth points towards East and it increases counter-clockwise.

NED frame is the “intuitive” North-East-Down orientation where the zero azimuth points to North and increases clockwise, just as you are used to when using a compass.

Magnetic azimuth is the angle between Earth’s magnetic North (or East in ENU frame) and a specified direction.

True azimuth (also called geographic, map or geodetic North) is the angle between Earth’s geographic North (or East in ENU frame) and a specified direction.

UTM azimuth (also called grid azimuth) is the angle between UTM North (or East in ENU frame) and a specified direction. UTM is a planar projection of Earth’s surface onto predefined rectangles, which yields a Cartesian coordinate system. The Earth is divided into several stripes which are unrolled into a plane to form the UTM grid. These stripes are called UTM zones. Each UTM zone is 6 degrees of longitude wide, but it is considered valid in a slightly larger area, approximately 100 km outside its precise bounds. This allows sticking to a single UTM zone to prevent zone switching when moving close to the boundary of two zones.

The difference between magnetic and true North is called magnetic declination. Its values are location- and time-dependent and they are approximated by the World Magnetic Model.

The difference between true North and grid North is called grid convergence. Its values are only location-dependent and do not differ in time. The values also depend on the chosen UTM zone.

Although ROS specifies that all angular values should be expressed in radians, the usage of degrees in geography is so common that Azimuth messages support both radians and degrees.

For more information, see https://www.drillingformulas.com/magnetic-declination-and-grid-convergent-and-their-applications-in-directional-drilling/ or https://en.wikipedia.org/wiki/Azimuth .