sfMM-calcRadius_cpp: Compute geometric caracteristics of a spatial group
In bozenne/MRIaggr: Management, Display, and Processing of Medical Imaging Data

C++ function that computes the barycenter of a spatial group. For internal use.

1	calcRadius_cpp(coords, sample, threshold, subset_bary, verbose)

`coords`	the spatial coordinates of the observations. matrix with a number of rows equal to the length of `sample`.
`sample`	the weight of each voxel in the computation of the barycenter. positive numeric.
`threshold`	observations with a `sample` value below the value of `threshold` are discarded. numeric.
`subset_bary`	an indicator of the observations that should be kept ? logical vector.
`verbose`	should the radius of the spatial group be printed ? logical.