A method for thickness determination of overlayers on irregularly shaped samples is established using AES depth profiling and stereophotogrammetry. The analysis is performed on a small selected area assumed to be flat. The angle of ion incidence on the area, given by the scalar product of the ion beam vector and the normal to the surface, is obtained by determining the normal using a sterological method based on rotation of a titled sample. The variation in etch rate with the angle of ion incidence is determined for various oxides on flat samples. Application studies show that the angle of ion incidence on gas-atomized metal particles can be determined from their spherical shape; the variation in etch rate is found to agree well with that calibrated on flat surfaces. It is also demonstrated how the presented method can be used when determining the oxide thickness in different areas on highly irregular water-atomized metal particles.