
Journal for Geometry and Graphics 12 (2008), No. 2, 123132 Copyright Heldermann Verlag 2008 Orthogonal Line Congruences with Common Middle Surface Pelagia Koltsaki Dept. of Mathematics, Faculty of Science, Aristotle University, 54124 Thessaloniki, Greece kopel@math.auth.gr Despina Papadopoulou Dept. of Mathematics, Faculty of Science, Aristotle University, 54124 Thessaloniki, Greece papdes@math.auth.gr Let S, S' be two orthogonal line congruences with common middle surface P(u,v). We study S and S' firstly in the case that S is isotropic and then in the case that S is the normal line congruence of P(u,v). Keywords: Orthogonal line congruences, middle surface, middle envelope. MSC: 53A25 [ Fulltextpdf (137 KB)] for subscribers only. 