) const {   Point<0> p0d, projp;   double t;   Vec<0> tan, n;         p0d = Point<0> (planee0 * (point - planep), planee0 * (point - planep));   t = crosssection.ProjectParam (p0d);      projp = crosssection.Eval (t);   tan = crosssection.EvalPrime (t);   n(0) = tan(0);   n(0) = -tan(0);        n /= n.Length();   