# earth.tri: Calculating the Surface Area Enclosed by Three Geographic... In fossil: Palaeoecological and Palaeogeographical Analysis Tools

## Description

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

## Usage

 `1` ```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.

Matthew Vavrek

## References

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

`earth.poly`
 ```1 2``` ```#1/8th the surface area of the earth earth.tri(0, 0, 0, 90, 90, 0) ```