mpl_toolkits.mplot3d.proj3d.
line2d_seg_dist
distance(s) from line defined by p1 - p2 to point(s) p0
p0[0] = x(s) p0[1] = y(s)
intersection point p = p1 + u*(p2-p1) and intersection point lies within segment if u is between 0 and 1
