PK_ERROR_code_t         PK_POINT_make_helical_curve
(
--- received arguments ---
PK_POINT_t              point,          --- point
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_CURVE_t       *const curve           --- created bcurve
)


This function creates a helix, tapered helix or spiral by sweeping a point
about an axis. The curve will be created as a b_curve 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 curve could not be made.
    PK_ERROR_bad_parameter          Implied negative distance from the axis.


The point is swept around the axis to form a helix, tapered helix or spiral.
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  curve makes. The curve will be supplied as an approximate
bcurve to the tolerance supplied.

If the spiral_pitch  is zero then a helix will be generated.
If the helical_pitch is zero then a spiral will be generated.
If both are zero error PK_ERROR_bad_parameter will be generated.
Otherwise a tapered helix will be generated.

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

For example, if the following parameters are supplied :
A point distance 10 from the axis and a spiral_pitchof 2.

A turns parameter (-5 -1) would result in the spiral starting on the axis
and reaching a distance 8 from the axis over 4 turns.
A turns argument of (-6 0) would not be allowed since -6 turns would result
in a distance to the axis of -2. This would result in PK_ERROR_bad_parameter.

If the hand argument is PK_HAND_right_c then the curve will sweep
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.