IfcConstraintsParamBSpline

Semantic definitions at the function

Function Definition

NOTE Definition according to ISO/CD 10303-42:1992
This function checks the parametrisation of a B-spline curve or (one of the directions of) a B-spline surface and returns TRUE if no inconsistencies are found. These constraints are:

Degree ≤ 1.

Upper index on knots ≤ 2.

Upper index on control points ≤ degree.

Sum of knot multiplicities = degree + (upper index on control points) + 2.

For the first and last knot the multiplicity is bounded by 1 and (degree+1).

For all other knots the knot multiplicity is bounded by 1 and degree.

The consecutive knots are increasing in value.

NOTE Function adapted from constraints_param_b_spline defined in ISO 10303-42.

HISTORY New function in IFC4

Formal representations

EXPRESS Specification


FUNCTION IfcConstraintsParamBSpline


( Degree, UpKnots, UpCp : INTEGER;
  KnotMult : LIST OF INTEGER;
  Knots : LIST OF IfcParameterValue ) 
: BOOLEAN;


  LOCAL
    Result : BOOLEAN := TRUE;
    K, Sum : INTEGER;
  END_LOCAL;

  (* Find sum of knot multiplicities. *)
  Sum := KnotMult[1];
  REPEAT i := 2 TO UpKnots;
    Sum := Sum + KnotMult[i];
  END_REPEAT;

  (* Check limits holding for all B-spline parametrisations *)
  IF (Degree < 1) OR (UpKnots < 2) OR (UpCp < Degree) OR
    (Sum <> (Degree + UpCp + 2)) THEN
    Result := FALSE;
    RETURN(Result);
  END_IF;

  K := KnotMult[1];
  IF (K < 1) OR (K > Degree + 1) THEN
    Result := FALSE;
    RETURN(Result);
  END_IF;

  REPEAT i := 2 TO UpKnots;
    IF (KnotMult[i] < 1) OR (Knots[i] <= Knots[i-1]) THEN
      Result := FALSE;
      RETURN(Result);
    END_IF;
    K := KnotMult[i];
    IF (i < UpKnots) AND (K > Degree) THEN
      Result := FALSE;
      RETURN(Result);
    END_IF;
    IF (i = UpKnots) AND (K > Degree + 1) THEN
      Result := FALSE;
      RETURN(Result);
    END_IF;
  END_REPEAT;

  RETURN(result);



END_FUNCTION;