A 'rhumb line' (or loxodrome) is a path of constant bearing, which crosses all meridians at the same angle.
Usage
distRhumb(p1, p2, r=6378137)
Arguments
p1
longitude/latitude of point(s), in degrees; 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. Should be of same length of p1, or a single point (or vice versa when p1 is a single point
r
radius of the earth; default = 6378137 m
Value
distance value in units of r (default=meters)
Details
Rhumb (from the Spanish word for course, 'rumbo') lines are straight lines on a Mercator Projection map. They were used in navigation because it is easier to follow a constant compass bearing than to continually adjust the bearing as is needed to follow a great circle, though rhumb lines are normally longer than great-circle (orthodrome) routes. Most rhumb lines will gradually spiral towards one of the poles.