PK_ERROR_code_t         PK_CURVE_make_helical_surf
(
--- received arguments ---
PK_CURVE_t              curve,          --- curve
PK_INTERVAL_t           curve_interval, --- curve interval
const PK_AXIS1_sf_t    *axis,           --- axis
PK_HAND_t               hand,           --- handedness
PK_INTERVAL_t           turns,          --- range of turns
double                  helical_pitch,  --- height of a single turn
double                  spiral_pitch,   --- increase in radius of a single turn
double                  tolerance,      --- used in approximations

--- returned arguments ---
PK_SURF_t        *const surface         --- created surface
)


This function creates a helix, tapered helix or spiral surface by sweeping a
part of a curve about an axis. The surface will be created as a b_surface to
a tolerance supplied by the user.


Specific Errors:
    PK_ERROR_tolerances_too_tight   The requested tolerance could not be met.
    PK_ERROR_cant_make_bspline      The requested surface could not be made.
    PK_ERROR_bad_parameter          Implied negative distance from the axis.


The interval of the curve is swept around the axis to form a helix, tapered
helix or spiral surface.

The helical_pitch is the distance along the axis moved in one turn and the
spiral_pitch is the distance moved away from the axis in one turn. These
distances may be negative. The turns argument specifies how many complete
revolutions the surface makes. The surface will be supplied as an approximate
bsurface to the tolerance supplied.

If the spiral_pitch  is zero then a helical sweep is produced.
If the helical_pitch is zero then a spiral sweep is produced.
If both are zero then error PK_ERROR_bad_parameter results.
Otherwise a tapered helical sweep is produced.

The turns argument need not include position 0.0 - the supplied curve, but
must not imply a negative distance from the axis.

If the hand argument is PK_HAND_right_c then the curve will be swept
clockwise when viewed along the axis.

The performance of helical curves in modelling operations is optimised if the
turns argument uses whole numbers for both ends of the interval.