AcGeEntity3d AcGePointEnt3d AcGePointOnSurface
class AcGePointOnSurface : public AcGePointEnt3d;
geponsrf.h
Represents a point on a surface. This class encapsulates all of the geometric information of a point on a surface, including its parameter value, 3D coordinates, derivatives, and normal vector.
Geometry library documentation in ObjectARX Developer's Guide