Geometry to relate rotation durations and direction-finding angles to a physical source size and to the WCRS correction. (a) A corotating source at heliocentric radius r = R_model(f) rotates through Δϕ = Ω_⊙T/24 during an interval of duration T (in hours), corresponding to a transverse chord length ﹩{W}_{{\rm{rot}}}=2r\sin ({\rm{\Delta }}\phi /2)﹩. (b) The same chord subtends a geometric angular half-width γ_rot at the spacecraft (Sun–spacecraft distance D_SC); comparing with the goniopolarimetric apparent half-width γ defines the angular-broadening factor ﹩{ \mathcal B }\equiv \gamma /{\gamma }_{{\rm{rot}}}﹩. (c) Schematic of the WCRS construction: the measured direction finding ray (dashed purple) has an angular deviation ψ from the Sun–spacecraft line; applying the scattering correction shrinks the deviation to ψ_corr = ψ/Ξ_F (solid blue). Intersecting the corrected ray with the density model sphere ∣r∣ = R_model(f) yields the near- and farside solutions r_close and r_far.