loxodrome: a standalone construct

A loxodrome, or rhumb line, is the path on the Earth's surface that crosses every meridian at the same angle, so it is the track a ship or aircraft follows when it holds a single constant compass bearing. On a Mercator chart it plots as a straight line, which is precisely why that projection is favoured for navigation, and it is longer than the great-circle (shortest) route except along a meridian or the equator. First studied by Pedro Nunes in the sixteenth century, its geometry on the ellipsoid was worked out by Bowring. The referent is the constant-bearing curve on a sphere or ellipsoid.[1]

Unit

The constant azimuth that defines the track, together with its arc length

Recovery means

Not applicable

Measured by

Computed from a fixed azimuth across the meridians; its length follows from the change in latitude and the bearing