struct PK_AXIS2_sf_s
    {
    PK_VECTOR_t  location;          --- a cartesian point.
    PK_VECTOR1_t axis;              --- a direction.
    PK_VECTOR1_t ref_direction;     --- a direction.
    };
typedef struct PK_AXIS2_sf_s PK_AXIS2_sf_t;


This data structure is the standard form for the location and orientation
of two mutually perpendicular axes.


Specific Errors:
PK_ERROR_vectors_not_orthogonal   axis and ref_direction are not othogonal


This corresponds to STEP's axis2_placement structure.