OUBSCU ( curve, tol, nopts, iopts, ctrl, dim, order, nctrl, knots, props,
==========================================================================
nprops, ifail )
===============
Outputs a curve in B-spline form.
Receives:
KI_tag_curve *curve --- curve
KI_dbl_distance *tol --- tolerance for approximation
<KI_int_nitems> *nopts --- number of options in 'iopts'
KI_cod_srop iopts[nopts] --- conversion options
Returns:
KI_tag_list_dbl *ctrl --- control points
KI_int_dimension *dim --- dimension of control points
KI_int_order *order --- order of bspline curve
KI_int_nitems *nctrl --- number of control points
KI_tag_list_dbl *knots --- knot vector
<KI_tag_list_int> *props --- list of curve properties
<KI_int_nitems> *nprops --- number of curve properties
KI_cod_error *ifail --- failure code
Specific errors:
KI_tolerances_too_tight tolerance too tight
KI_cant_make_bspline failed to convert geometry
Description:
The supplied curve is output in B-spline form.
If the curve is of type 'TYCUTR' (trimmed curve) then the resulting
B-spline curve will be bounded by the end points of the trimmed curve.
The B-spline will represent the curve exactly if possible, but it may be
necessary to approximate it. If so, 'tol' specifies an upper bound on the
distance between the B-spline and the original curve, which this function
will usually satisfy although this is not guaranteed. During the approximation
process, the curve is subdivided and each segment approximated by a cubic
B-spline curve. If the required tolerance cannot be met when any of these
segments is less than about one millionth of the parameter range then the
function will fail with error KI_tolerances_too_tight indicating that a
larger tolerance may allow a successful approximation.
Representations of lines and the rational forms of circles and ellipses
are exact. When the representation of a B-curve is changed it will,
in general, only be exact when its order is not decreased.
The format of the output curve is selected by options in 'iopts'. Options
allowed are:-
Option | Description
--------|---------------------------------------
SROPCU | Force output of B-splines of degree 3
SROPNR | Force output of non-rational B-splines
The effects of these options on the representations produced for different
curve types are:-
| none | SROPCU | SROPCU | SROPNR
| | | SROPNR |
-----------------------------------------------------------------------------
line | linear | cubic | cubic | linear
| | | |
circle | rational | rational | cubic | cubic
| cubic | cubic | |
| | | |
ellipse | rational | rational | cubic | cubic
| cubic | cubic | |
| | | |
B-curve | no change | cubic | cubic | rational to
| | | | cubic
| | | |
all other | cubic | cubic | cubic | cubic
curves * | | |
* If an intersection curve or SP-curve lies on a B-surface and coincides with
a constant parameter line on that B-surface, the equivalent B-curve will
be extracted from the surface. In this case, the options will apply to the
extracted B-curve. Thus exact representations of these curves will be possible
in certain cases.
The meaning of the values in the arguments 'ctrl', 'dim', 'order', 'nctrl'
and 'knots' are given under OUBSPC.
Properties list 'props':
The following properties may be returned:
. PAPRPE - the B-spline is periodic. If this token is not present then the
B-spline is not periodic.
. PAPREX - the B-spline is an exact representation of the original curve.
If this token is not present, then the B-spline approximates the
original, with the maximum error bounded by 'tol'.
Number of properties 'nprops':
. Gives the number of properties in the 'props' list.
