Calculates sample variance of points' distances in 3D space from their centroid. This function is normally only used indirectly through validate_get_twcv.

point_3d_variance(point_matrix)

## Arguments

point_matrix

An n-by-3 numerical matrix where each row corresponds to a single point in 3D space.

## Value

A one-element numeric vector holding calculated variance

## Details

The variance here is taken to mean the sum of variances for each dimension/axis: $$\frac{\sum_{i=1}^n (x_i-x_m)^2 + (y_i-y_m)^2 + (z-z_m)^2}{n-1}$$ Where $$X/Y/Z$$ represent one axis each, $$a_m$$ represents the mean of all points' coordinates on an axis, and $$n$$ represents the total number of points.

centroid_3d_sq_dist