# sl.triag.area: Compute Triangle Area on Sphere In helgegoessling/spheRlab: Spherical Geometry, Analysis, and Plotting of Geoscientific Data on Arbitrary Grids

## Description

Compute the area of a triangle on a sphere.

## Usage

 `1` ```sl.triag.area(lon, lat) ```

## Arguments

 `lon` a vector of length 3 specifying the longitudes of the triangle vertices. `lat` a vector of length 3 specifying the longitudes of the triangle vertices.

## Details

This function is based on Girard's theorem: the area of a triangle on a unit sphere equals the excess of the sum of angles over `pi` (180 degrees).

## Value

A scalar giving the area of the triangle (on a unit sphere).

## Note

This function is more accurate for large triangles but less accurate for small ones compared to `sl.smalltriag.area`. Also, `sl.smalltriag.area` is computationally cheaper, so for small triangles (<1/100 degrees or so), `sl.smalltriag.area` should be preferred in any case.

## Author(s)

Helge Goessling

`sl.smalltriag.area`, `sl.polygon.area`
 ```1 2 3``` ```sl.triag.area(c(0,60,30),c(0,0,30)) ## Should return: ## [1] 0.2866951 ```