Internal function to define the points of view
pov_selecter(mesh, grid, start.points = 250, method = "ast3d")
selection numeric: positioning vector of the selected points of the grid
object of class mesh3d
matrix: a 3D grid
numeric: number of center to be found
character: select "a" or "c" for respectively AST-3D and CA-LSE method
Antonio Profico, Costantino Buzi, Marina Melchionna, Paolo Piras, Pasquale Raia, Alessio Veneziano