Geometry of the transition disk model. Panel a Sketch of the rotationally symmetric, inclined disk model with inclination i, wall slope χ, and angular height of the disk wall a. Panel b Corresponding vertical disk cross-section with the midplane disk distance to the star r and the height h for the surface point S (r, h), and radii r₀ and r_w for the inner radius and the rim radius of the wall, respectively. Emitted photons from the star are characterized by the angular direction ϑ, while θ₀ and θ are the polar incidence and emergence angles from surface point S for the special case of scattering in the principal plane.