SD : scale domain, integer in [1,3] (variable l (lowercase "L") in paper)
tSD: curvature tolerance for scale domain SD
t1 = specified by user
t2 = t1 + 0.1
t3 = t2 + 0.1
CRSD : cell resolution for scale domain SD (lambda variable in paper)
CR1 = 0.5 * CR2
CR2 = specified by user (nominal post-spacing of input LiDAR data)
CR3 = 1.5 * CR2
f : tension parameter (invariant across scale domains)
f = 1.5
U : vector of points that remain unclassified
U = (P1 , P2 , P3 , ... Pn)
n : # of points in U (at the start of each loop pass)
Pj : single LiDAR point
Pj = (xj , yj , zj)
U0 = initial point-cloud data specified by user