Evaluation of sky view factors by projection. Red arrow: normal vector n above the point q on a surface. Blue quadrilaterals: two windows of solid angle Ω ≈ 0.16 sr through which the sky can be seen from q (i.e., 𝒯 = 1); the right window is tilted against n by γ = 60°. Green rectangles: projection of the windows onto the tangential plane with areas π F_sky ≈ Ω and Ω × cos(60° ) = Ω/2, respectively.