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\name{distRhumb}
\Rdversion{1.1}
\alias{distRhumb}
\title{
Distance along a rhumb line
}
\description{
A rhumb line (loxodrome) is a path of constant bearing (direction), which crosses all meridians at the same angle.
}
\usage{
distRhumb(p1, p2, r=6378137)
}
\arguments{
\item{p1}{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}
\item{p2}{as above; or missing, in which case the sequential distance between the points in p1 is computed}
\item{r}{radius of the earth; default = 6378137 m}
}
\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, even though rhumb lines are normally longer than great-circle (orthodrome) routes. Most rhumb lines will gradually spiral towards one of the poles.
}
\value{
distance in units of r (default=meters)
}
\references{
\url{http://www.movable-type.co.uk/scripts/latlong.html}
}
\author{
Robert Hijmans and Chris Veness
}
\seealso{
\code{\link[geosphere]{distCosine}, \link[geosphere]{distHaversine}, \link[geosphere]{distVincentySphere}, \link[geosphere]{distVincentyEllipsoid}}
}
\examples{
distRhumb(c(10,10),c(20,20))
}
\keyword{ spatial }
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