Right-handed vs. Left-handed CRS

Right-handed CRS

The name derives from the right-hand rule (mathematics and physics). If the index finger of the right hand is pointed forward, the middle finger bent inward at a right angle to it, and the thumb placed at a right angle to both, the three fingers indicate the relative directions of the x-, y-, and z-axes in a right-handed system. The thumb indicates the x-axis, the index finger the y-axis and the middle finger the z-axis. Conversely, if the same is done with the left hand, a left-handed system results.

When applied to a geodetic Coordinate Reference System (CRS) for which the z axis points from the centre of the Earth outwards, this implies that right-handed systems will have longitude (East) as first axis and latitude (North) as second axis. This is not the usual aviation convention, as latitude is usually used in aviation as first axis and angles/bearings are measured clockwise towards East (the second axis).

Left-handed CRS

See the explanations for right-handed CRS above. Left-handed CRS are the natural choice for the aeronautical data domain.