Surface brightness map of the stellar disk in NGC 551 in an edge-on orientation. The left panel shows the surface brightness map, whereas the middle panel represents a 2D fit to the map (using Eq. 14). The right panel shows the residual of the fitting. The masked portion in the middle of each panel represents the region where we did not solve the hydrostatic equilibrium equation. The 2D fit describes the simulated data reasonably well.