(a) A house with a concave-down base. (b) A house with a flat base and a wavy line beneath it. (c) A house with a wavy line beneath it, with a flat base below the line. (d) A house with a wavy line beneath it, with a concave-up base below the line.
Exposure classes of E3-surface condition: (a) convex; (b) flat and permeable; (c) flat and impermeable; and (d) concave.Source: Davis et al. (2023)