central.angle: Central angle between two points on a sphere
Description
On a sphere the central angle between two points is defined as the
angle whose vertex is the centre of the sphere and that subtends
the arc formed by the great circle between the points. This
function computes the central angle for two points $(\phi_1,
\lambda_1)$ and $(\phi_2,\lambda_2)$.Usage
central.angle(phi1, lambda1, phi2, lambda2)
Arguments
phi1
Lattitude of first point
lambda1
Longitude of first point
phi2
Lattitude of second point
lambda2
Longitude of secone point
source
Wikipedia http://en.wikipedia.org/wiki/Central_angle