Functions to calculate different types of area for polygons.

## Usage

```
signed_area(x)
unsigned_area(x)
signed_area_cd(x)
unsigned_area_cd(x)
signed_area_geodesic(x)
unsigned_area_geodesic(x)
```

## Details

functions assume counter clock-wise winding in accordance with the simple feature access standard

functions ending in

`_cd`

use the Chamberlain-Duquette algorithm for spherical areaChamberlain-Duquette and Geodesic areas are returned in meters squared and assume non-planar geometries

See geo docs for more:

## Examples

```
x <- c(0, 1, 1, 0, 0)
y <- c(0, 0, 1, 1, 0)
p <- geom_polygon(x, y)
signed_area(p)
#> [1] 1
unsigned_area(p)
#> [1] 1
signed_area_cd(p)
#> [1] 12391399902
unsigned_area_cd(p)
#> [1] 12391399902
signed_area_geodesic(p)
#> [1] 12308778361
unsigned_area_geodesic(p)
#> [1] 12308778361
```