Get the initial bearing (direction; azimuth) to go from point `p1`

to point `p2`

(in longitude/latitude) following the shortest path on an ellipsoid (geodetic). Note that the bearing of travel changes continuously while going along the path. A route with constant bearing is a rhumb line (see `bearingRhumb`

).

`bearing(p1, p2, a=6378137, f=1/298.257223563)`

Bearing in degrees

- p1
longitude/latitude of point(s). Can be a vector of two numbers, a matrix of 2 columns (first one is longitude, second is latitude) or a SpatialPoints* object

- p2
as above. Can also be missing, in which case the bearing is computed going from the first point to the next and continuing along the following points

- a
major (equatorial) radius of the ellipsoid. The default value is for WGS84

- f
ellipsoid flattening. The default value is for WGS84

Robert Hijmans

C.F.F. Karney, 2013. Algorithms for geodesics, J. Geodesy 87: 43-55. tools:::Rd_expr_doi("10.1007/s00190-012-0578-z"). Addenda: https://geographiclib.sourceforge.io/geod-addenda.html. Also see https://geographiclib.sourceforge.io/

` bearingRhumb `