Plane equation:
(1) lx + my + nz = d
where d is a distance from an origin to the plane,
{l,m,n} is direction consines, and
sqrt(l*l + m*m + n*n)=1.
(2) ax + by + cz = 1
where d presented in (1) can be calculated by 1/sqrt(a*a + b*b + c*c).
(3) Ax + By + Cz = d^2
where (A, B, C) denotes a vector from an origin to the plane, which can be obtained by A = l*d, B=m*d, and C=n*d.
For a point cloud, P0, P1, P2, ~ Pn,
Its centroid C, (cx, cy, cz), is on an expected least squre fitted plane.
Therefore, dot product of [l, m, n] and (Pi-C) is zero.
l*xi + m*yi + n*zi = 0
whrer (xi,yi,zi) = Pi
To avoid [l, m, n] are estimated as zero,
a constraint of direction consines is adopted,
l^2 + m^2 + n^2 = 1.0
