earth.tri {fossil}

Calculating the Surface Area Enclosed by Three Geographic Points

Description

Calculate the true area on a sphere enclosed by three points on the earth's surface

Usage

earth.tri(long1, lat1, long2, lat2, long3, lat3)

Arguments

long1

Longitude of site 1

lat1

Latitude of site 1

long2

Longitude of site 2

lat2

Latitude of site 2

long3

Longitude of site 3

lat3

Latitude of site 3

Details

A function to find the area enclosed by three points on the surface of the earth, given their latitudes and longitudes. This function is primarily designed to be a component of earth.poly, which is likely a more useful function for most applications.

Value

Returns a value in kilometers squared of the area enclosed by the three points.

Note

The distance calculated may be up to 0.2% inaccurate, as this function treats the Earth as a sphere with a circumference of 40041.47 km (mean circumference), rather than an ellipsoid like it actually is.

Author(s)

Matthew Vavrek

References

Wolfram Mathworld, http://mathworld.wolfram.com/SphericalTriangle.html

See Also

earth.poly

Examples

#1/8th the surface area of the earth
earth.tri(0, 0, 0, 90, 90, 0)