GIS::Distance::Cosine - Spherical law of cosines distance calculations.
Although this formula is mathematically exact, it is unreliable for small distances. See GIS::Distance::MathTrig for related details.
A faster (XS) version of this formula is available as GIS::Distance::Fast::Cosine.
Normally this module is not used directly. Instead GIS::Distance is used which in turn interfaces with the various formula classes.
a = sin(lat1) * sin(lat2) b = cos(lat1) * cos(lat2) * cos(lon2 - lon1) c = arccos(a + b) d = R * c