  Detailed analysis of scanning probe microscopy (SPM) data acquired for tilted
and non-flat surfaces is usually complicated due to presence of large number of
surface areas tilted by large/variable angles relative to the scanning plane.
As a consequence, standard methods of elimination of global/local slope by a
plane subtraction or numerical differentiation seems to be ineffective. We
demonstrate that simple difference-of-gaussians procedure provides us output
data corresponding to a projection of considered surface onto scanning plane
without undesirable modifications of contrast. This method allows us to
minimize small-scale noise, finite slopes of SPM image along both fast and slow
scanning directions and eliminate surface rippling. This method can be applied
both for fast 'on-the-fly' visualization of experimental data and more detailed
analysis, including high precision determination of lattice parameters and
angles between translations vectors in different surface domains. In order to
estimate geometrical distortions related to the difference-of-gaussians
approach, we compare this method with direct image rotation in 3D space.
