geosphere (version 1.5-10)

distVincentyEllipsoid: 'Vincenty' (ellipsoid) great circle distance

Description

The shortest distance between two points (i.e., the 'great-circle-distance' or 'as the crow flies'), according to the 'Vincenty (ellipsoid)' method. This method uses an ellipsoid and the results are very accurate. The method is computationally more intensive than the other great-circled methods in this package.

Usage

distVincentyEllipsoid(p1, p2, a=6378137, b=6356752.3142, f=1/298.257223563)

Arguments

p1

longitude/latitude of point(s), in degrees 1; 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; or missing, in which case the sequential distance between the points in p1 is computed

a

Equatorial axis of ellipsoid

b

Polar axis of ellipsoid

f

Inverse flattening of ellipsoid

Value

Distance value in the same units as the ellipsoid (default is meters)

Details

The WGS84 ellipsoid is used by default. It is the best available global ellipsoid, but for some areas other ellipsoids could be preferable, or even necessary if you work with a printed map that refers to that ellipsoid. Here are parameters for some commonly used ellipsoids:

	ellipsoid	a	b	f
	WGS84	6378137	6356752.3142	1/298.257223563
	GRS80	6378137	6356752.3141	1/298.257222101
	GRS67	6378160	6356774.719	1/298.25
	Airy 1830	6377563.396	6356256.909	1/299.3249646
	Bessel 1841	6377397.155	6356078.965	1/299.1528434
	Clarke 1880	6378249.145	6356514.86955	1/293.465
	Clarke 1866	6378206.4	6356583.8	1/294.9786982
	International 1924	6378388	6356911.946	1/297
	Krasovsky 1940	6378245	6356863	1/298.2997381

a is the 'semi-major axis', and b is the 'semi-minor axis' of the ellipsoid. f is the flattening. Note that f = (a-b)/a

more info: http://en.wikipedia.org/wiki/Reference_ellipsoid

References

Vincenty, T. 1975. Direct and inverse solutions of geodesics on the ellipsoid with application of nested equations. Survey Review Vol. 23, No. 176, pp88-93. Available here:

http://www.movable-type.co.uk/scripts/latlong-vincenty.html

http://en.wikipedia.org/wiki/Great_circle_distance

See Also

distGeo, distVincentySphere, distHaversine, distCosine, distMeeus

Examples

# NOT RUN {
distVincentyEllipsoid(c(0,0),c(90,90))
# on a 'Clarke 1880' ellipsoid
distVincentyEllipsoid(c(0,0),c(90,90), a=6378249.145, b=6356514.86955, f=1/293.465)
# }