struct PK_PLANE_sf_s
    {
    PK_AXIS2_sf_t   basis_set;  --- a point, reference direction and a normal
    };

typedef struct PK_PLANE_sf_s PK_PLANE_sf_t;



See documentation for PK_AXIS2_sf_t.

The parameterisation of a plane is as follows:

    P = basis_set.location
    x = basis_set.ref_direction
    y = basis_set.axis X basis_set.ref_direction  ( cross product )

    S( u, v) = P + ux + vy