Given twp P1 = (x1,y1,z1), P2 = (x2,y2,z2)
x = x1 + t xv y = y1 + t yv z = z1 + t zv
Given a point P1 and a vector V = [xv, yv, zv] COMPACT FORM: L = P1 + t[P2 - P1] or L = P1 + Vt
