The definition of a conchoid surface is:
rc[u, v] = r[u, v] + k (r[u, v] - P)/Norm[r[u, v] - P] and rc[u, v] = r[u, v] - k (r[u, v] - P)/Norm[r[u, v] - P] , P is the pole, k distance and r[u, v] the base surface.
In this notebook we will obtain the conchoid surface of the hyperbolic paraboloid:
{u, v, u v + 1} with the distance k = 1.5 and as pole P = {0, 0, 1}.
