A direction cosine matrix is an orthogonal three-dimensional matrix.
(<=> (3d-Direction-Cosine ?Dircos) (And (Orthogonal-Matrix ?Dircos) (Row-Dimension ?Dircos 3)))
(Orthogonal-Matrix ?Dircos)
(Nth-Domain Orientation 3 3d-Direction-Cosine) (<= (Row-Dimension $X 3) (3d-Direction-Cosine $X)) (<=> (3d-Direction-Cosine ?Dircos) (And (Orthogonal-Matrix ?Dircos) (Row-Dimension ?Dircos 3))) (Nth-Domain Simple-Rotation 3 3d-Direction-Cosine) (=> (= (Simple-Rotation ?Axis ?Angle) ?Dircos) (3d-Direction-Cosine ?Dircos))