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) or a sphere (great circle). Note that the bearing of travel changes continuously while going along the path. A route with constant bearing is a rhumb line (see bearingRhumb).
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
a
major (equatorial) radius of the ellipsoid. The default value is for WGS84
f
ellipsoid flattening. The default value is for WGS84
sphere
logical. If TRUE, the bearing is computed for a sphere, instead of for an ellipsoid