I don't know the proper term for "spreaded" but what I want to find is, a value that indicates how far is an average point from the centroid.
I think this is standard deviation of the point set, but I need metrics.
For instance, consider the figures:
Here, blue points are centroids and black points are the points in the cloud.
In both cases, standard deviation is the same, but the first cloud is more "spreaded".
If a spread factor $\alpha$ were to be given, how would you compute $\alpha$ given the 3D coordinates of the points?