distCosine: 'Law of cosines' great circle distance
The shortest distance between two points (i.e., the 'great-circle-distance' or 'as the crow flies'), according to the 'law of the cosines'.
This method assumes a spherical earth, ignoring ellipsoidal effects.
distCosine(p1, p2, r=6378137)
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
radius of the earth; default = 6378137 m
Vector of distances in the same unit as r (default is meters)