Interpolation on finite elements usually occurs in a Hilbert space setting, which means that interpolation techniques involving orthogonal projection are an
alternative for the traditional Lagrange nodal interpolation schemes. In addition to the Lagrange interpolation, this paper discusses the global orthogonal projection
and the projection-based interpolation. These techniques are compared from the point of view of quality, efficiency, sensitivity to input parameters and other
aspects. Local optimality result for the projection-based interpolation is presented.