Mainly for internal use. Determines the centroids of a polygon based on
its x and y coordinates.
This function is a reimplementation of `soiltexture::TT.polygon.centroids()`
and only re-implemented to avoid extra dependencies.
Usage
poly_centroid(poly_x, poly_y)
Value
A numeric, the area of the polygon.
Arguments
poly_x
(numeric) X coordinates of each vertices of the polygon
poly_y
(numeric) Y coordinates of each vertices of the polygon