Ingress (or egress) duration as a function of the signed oblateness parameter ﹩\tilde{f}﹩ and the impact parameter b for circular orbits in the Radon transform limit. Over each of ingress and egress, the projected velocity is assumed to be constant (Equation (27)). The projected planetary shape is an ellipse with position angle ϕ = 0^∘ or 90^∘, measured from the x-axis. We define f = 1 − R_minor/R_major ≥ 0 and use ﹩\tilde{f}=f﹩ for ϕ = 0^∘ and ﹩\tilde{f}=-f﹩ for ϕ = 90^∘. This convention allows the projected radii along the x- and y-axes to vary continuously on a single axis. The scaled semimajor axis a/R_s was adjusted so that the interval t_e − t_i remained fixed; its value is shown in the left panel. In these calculations, the planet-to-star area ratio was set to 0.01, and a/R_s = 15 at b = 0. White contours indicate parameter combinations that produce identical light curves in this approximation. The color scale is nonlinear for visual clarity.