NON-UNIFORM B-SPLINE SURFACE 3

PBSS3

CALL SEQUENCE

CALL PBSS3	(USORD, VSORD, UNKA, VNKA, UKNOTS, VKNOTS, RTYPE, UNCP, VNCP, P  XA, PYA, PZA, PWA, TCLDR, TCREC)

INPUT PARAMETERS

INTEGER USORD

U spline order

INTEGER VSORD

V spline order

INTEGER UNKA

Number of knots for u

INTEGER VNKA

Number of knots for v

REAL UKNOTS(UNKA)

U knots

REAL VKNOTS(VNKA)

V knots

INTEGER RTYPE

Rationality (PRAT,PNRAT)

INTEGER UNCP

U number of control points dimension

INTEGER VNCP

V number of control points dimension

REAL PXA (UNCP*VNCP)

REAL PYA (UNCP*VNCP)

REAL PZA(UNCP*VNCP)

REAL PWA(UNCP*VNCP)

Control points(MC)

INTEGER TCLDR

Number of array elements used in TCREC

CHARACTER*80TCREC(TCLDR)

Trimming curve data record

PHIGS STATE

EFFECT

This function specifies the non-uniform B-spline surface primitive.

The NON-UNIFORM B-SPLINE SURFACE element is inserted in the open structure after element pointer or replaces the element indicated by element pointer, depending on the edit mode value. Element pointer is updated and points to the NON-UNIFORM B-SPLINE SURFACE structure element. The values specified in the function are associated with the element.

The surface u and v orders must be positive integers. The u knots and the v knots must each form a non-decreasing sequence of numbers.

The RTYPE parameter may have the enumerated value PRAT or PNRAT. When PRAT is specified, the control points must be specified as homogeneous modelling coordinates (PXA,PYA,PZA,PWA), with the restriction that the fourth coordinate be greater than zero. For a PNRAT type, the control points are non-homogeneous PHIGS modelling coordinates (PXA,PYA,PZA).

The number of control points in each of the u and v directions must be at least as large as the corresponding order. The number of control points in each direction plus the corresponding order must equal the corresponding number of knots.

If a specified trimming curve approximation type is not available on a workstation, type WORKSTATION DEPENDANT is used.

When an element of this type is interpreted a non-uniform B-spline surface is generated. No surface is generated if either of the surface orders or any of the trimming curve orders are not supported. The effect of discontinuous trimming curves is workstation dependent. The current values of the non-uniform B-spline surface attributes specified in and stored in the traversal state list are bound to the primitive.

Attributes associated with Non-Uniform B-Spline Surface 3 :

INTERIOR STYLE

INTERIOR STYLE INDEX

INTERIOR COLOUR

EDGE FLAG

EDGE TYPE

EDGE WIDTH SCALE FACTOR

EDGE COLOUR

SURFACE APPROXIMATION CRITERIA

PARAMETRIC SURFACE CHARACTERISTICS

See PACK TRIM CURVE and UNPACK TRIM CURVE for a description of the trim curve data record.

EXTENSION TO THE PHIGS STANDARD

If used in NRS mode, the effect of this function is different from the effect described in the standard.

In NRS mode, (see OPEN PIPE), the element is not stored in a structure. It is sent to the workstation on which the pipe is opened.

ERRORS

5

Ignoring function, function requires state (PHOP,*, STOP,*)

500

Ignoring function, the specified order is less than one

501

Ignoring function, not enough control points for the specified order

502

Ignoring function, the specified order is inconsistent with number of knots and control points

503

Ignoring function, the knot sequence is not non-decreasing

507

Ignoring function, the fourth coordinate of a rational control point is less than or equal to zero

508

Ignoring function, a trimming curve order is less than 2

509

Ignoring function, a trimming curve does not contain enough control points for its specified order

510

Ignoring function, a trimming curve's order is inconsistent with its number of knots and control points

511

Ignoring function, a trimming curve's knot sequence is not non-decreasing

512

Ignoring function, a trimming curve's parameter range is inconsistent with its knots

138

Ignoring function, one or more of the fields in the specified data record is inconsistent with the specified type

SEE ALSO

open structure, open pipe (ext), non-uniform b-spline surface 3 with data, fill area set, set surface approximation criteria, set parametric surface characteristics, inquire current element content, inquire current element type and size