Spherical-toroidal geometry of the BNTorus model of Brightman & Nandra (2011; left). The reflector is a sphere with a conical opening of angle φ, whose section is shown in blue. The source of X-ray photons is the magenta star in the center, which is isotropic. The inclination angle i is defined as the angle between the normal to the plane of the torus and the observer. In RefleX, we model this shape by superimposing a number of annuli (right) that approximate the spherical-toroidal geometry.