The perimeter of the 2D shape is divided by the perimeter of a circle with
the same area as the shape. The more irregular the shape is, the closer the
output value is to zero. The closer the shape is to a circle, the closer
the output value is to 1.

## Arguments

- data
A data frame with the first two columns x and y coordinates, respectively.

## Value

A value between 0 (infinitely irregular) and 1 (a perfect circle).

## Examples

```
mcap_2d <- mesh_to_2d(mcap)
plot(mcap_2d, asp=1)
circularity(mcap_2d)
#> [1] 0.6085393
circ <- sim_circle() # simulate xy coordinates for a circle
plot(circ, asp=1)
circularity(circ)
#> [1] 0.9998321
```