distGeo: Distance on an ellipsoid (the geodesic)

Description

Highly accurate estimate of the shortest distance between two points on an ellipsoid (default is WGS84 ellipsoid). The shortest path between two points on an ellipsoid is called the geodesic.

Usage

distGeo(p1, p2, a=6378137, f=1/298.257223563)

Arguments

longitude/latitude of point(s). Can be a vector of two numbers, a matrix of 2 columns (first column is longitude, second column is latitude) or a SpatialPoints* object

as above

numeric. Major (equatorial) radius of the ellipsoid. The default value is for WGS84

numeric. Ellipsoid flattening. The default value is for WGS84

Value

Vector of distances in meters

Details

Parameters from the WGS84 ellipsoid are 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. rlll{ ellipsoid a f WGS84 6378137 1/298.257223563 GRS80 6378137 1/298.257222101 GRS67 6378160 1/298.25 Airy 1830 6377563.396 1/299.3249646 Bessel 1841 6377397.155 1/299.1528434 Clarke 1880 6378249.145 1/293.465 Clarke 1866 6378206.4 1/294.9786982 International 1924 6378388 1/297 Krasovsky 1940 6378245 1/298.2997381 } more info: http://en.wikipedia.org/wiki/Reference_ellipsoid

References

C.F.F. Karney, 2013. Algorithms for geodesics, J. Geodesy 87: 43-55. https://dx.doi.org/10.1007/s00190-012-0578-z. Addenda: http://geographiclib.sf.net/geod-addenda.html. Also see http://geographiclib.sourceforge.net/

Examples

Run this code

distGeo(c(0,0),c(90,90))

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