struct PK_BODY_loft_deriv_conds_s
    {
    PK_BODY_loft_curvature_t          curvature_condition;
    PK_BODY_loft_clamp_type_t         type;
    PK_BODY_loft_vector_clamp_t       vector_clamp;
    PK_BODY_loft_face_clamp_t         face_clamp;
    PK_BODY_loft_planar_clamp_t       planar_clamp;
    };

typedef struct PK_BODY_loft_deriv_conds_s PK_BODY_loft_deriv_conds_t;



This structure holds controls on the behaviour of the derivatives of the
lofted surfaces in the loft direction at a profile, or the profile direction at
a guide wire (which one is determined by context).


The derivative conditions structure has the following fields.

curvature_condition       Specifies the type of constraint to be applied
                            to curvature across the profile or guide.

                            For PK_BODY_loft_natural_c zero curvature is
                            implied and hence the natural loft end condition
                            is applied there. No further clamp conditions are
                            allowed. You cannot use natural curvature on
                            intermediate profiles, periodic lofts or on guide
                            wires.

                            For PK_BODY_loft_unconstrained_c (the default)
                            no end condition is imposed explicitly on the
                            curvature. Subsequent clamp conditions are then
                            examined.

type                      Indicates the type of clamp conditions to be
                            applied to the first derivative of the loft
                            surface across the profile or guide. The selection
                            of clamp condition indicates which of the
                            following fields actually holds the description
                            of constraint.

                            For PK_BODY_loft_clamp_vector_c the vector_clamp
                            field is examined for the description.

                            For PK_BODY_loft_clamp_face_c the face_clamp
                            field is examined for the description.

                            For PK_BODY_loft_clamp_planar_c the planar_clamp
                            field is examined for the description.

                            For PK_BODY_loft_clamp_no_c (the default)
                            no field is examined for the description. This is
                            the only allowed value when curvature_condition
                            is set to PK_BODY_loft_natural_c.

vector_clamp              Holds the first derivative constraint as a
                            collections of derivatives to be matched at each of
                            the vertices of the profile or guide.

face_clamp                Specifies a set of faces neighbouring the profile
                            or guide whose derivatives at their boundary, and
                            across the profile or along the guide, must be
                            matched by the loft surface.

planar_clamp              Specifies a normal vector that defines a plane
                            for clamping the loft, and a magnitude that
                            controls the size of the clamped derivatives.