gp_XY uv = helper.GetNodeUV( F, node, 0, &ok );
Handle(Geom_Surface) surface = BRep_Tool::Surface( F );
gp_Pnt p; gp_Vec du, dv, norm;
surface->D1( uv.X(),uv.Y(), p, du,dv );
norm = du ^ dv;
gp_XY uv = helper.GetNodeUV( F, node, 0, &ok );
Handle(Geom_Surface) surface = BRep_Tool::Surface( F );
gp_Pnt p; gp_Vec du, dv, norm;
surface->D1( uv.X(),uv.Y(), p, du,dv );
norm = du ^ dv;