The polar P(D) = {x : ⟨x, d⟩ ≤ 1 for all d ∈ D} of three unit vectors in the plane, as in Example 2.6. The cosine measure is the reciprocal of the distance to the farthest vertex; every farthest vertex, normalized, is a cosine vector.
drag an arrowhead · unit circle in gray · dashed circle through the farthest vertices