a x + b y + c z + d = 0

1

N^^(x, y, z) = (a/sqrt(a^2 + b^2 + c^2), b/sqrt(a^2 + b^2 + c^2), c/sqrt(a^2 + b^2 + c^2))

algebraic surfaces | constant (Gaussian) curvature surfaces | doubly ruled surfaces | linear surfaces | ruled surfaces