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IfcRectangularTrimmedSurface

Definition from ISO/CD 10303-42:1992: The trimmed surface is a simple bounded surface in which the boundaries are the constant parametric lines u1 = u1, u2 = u2, v1 = v1 and v2 = v2. All these values shall be within the parametric range of the referenced surface. Cyclic properties of the parameter range are assumed.

NOTE 1 For example, 370 degrees is equivalent to 10 degrees, for those surfaces whose parametric form is defined using circular functions (sine and cosine).

The rectangular trimmed surface inherits its parametrisation directly from the basis surface and has parameter ranges from 0 to |u2 - u1| and 0 to |v2-v1|.

NOTE 2 If the surface is closed in a given parametric direction, the values of u2 or v2 may require to be increased by the cyclic range.

NOTE Corresponding STEP name: rectangular_trimmed_surface. Please refer to ISO/IS 10303-42:1994, p.86 for the final definition of the formal standard.

HISTORY New class in IFC Release 2x.

Informal propositions:

  1. The domain of the trimmed surface shall be within the domain of the surface being trimmed.

EXPRESS specification:

ENTITY IfcRectangularTrimmedSurface
SUBTYPE OF ( IfcBoundedSurface);
BasisSurface  :  IfcSurface;
U1  :  IfcParameterValue;
V1  :  IfcParameterValue;
U2  :  IfcParameterValue;
V2  :  IfcParameterValue;
Usense  :  BOOLEAN;
Vsense  :  BOOLEAN;
DERIVE
Dim  :  IfcDimensionCount :=  BasisSurface.Dim;
WHERE
WR1  :  U1 <> U2;
WR2  :  V1 <> V2;
WR3  :  (('IFCGEOMETRYRESOURCE.IFCELEMENTARYSURFACE' IN TYPEOF(BasisSurface)) AND (NOT ('IFCGEOMETRYRESOURCE.IFCPLANE' IN TYPEOF(BasisSurface)))) OR ('IFCGEOMETRYRESOURCE.IFCSURFACEOFREVOLUTION' IN TYPEOF(BasisSurface)) OR (Usense = (U2 > U1));
WR4  :  Vsense = (V2 > V1);
END_ENTITY;

Attribute definitions:

BasisSurface  :  Surface being trimmed.
U1  :  First u parametric value.
V1  :  First v parametric value.
U2  :  Second u parametric value.
V2  :  Second v parametric value.
Usense  :  Flag to indicate whether the direction of the first parameter of the trimmed surface agrees with or opposes the sense of u in the basis surface.
Vsense  :  Flag to indicate whether the direction of the second parameter of the trimmed surface agrees with or opposes the sense of v in the basis surface.

Formal Propositions:

WR1  :  U1 and U2 shall have different values.
WR2  :  V1 and V2 shall have different values.
WR3  :  With exception of those surfaces closed in the U parameter, direction Usense shall be compatible with the ordered parameter values for U.
WR4  :  Vsense shall be compatible with the ordered parameter values for V.

Inheritance graph

ENTITY IfcRectangularTrimmedSurface;
ENTITY IfcRepresentationItem;
ENTITY IfcGeometricRepresentationItem;
ENTITY IfcSurface;
ENTITY IfcBoundedSurface;
ENTITY IfcRectangularTrimmedSurface;
BasisSurface  :  IfcSurface;
U1  :  IfcParameterValue;
V1  :  IfcParameterValue;
U2  :  IfcParameterValue;
V2  :  IfcParameterValue;
Usense  :  BOOLEAN;
Vsense  :  BOOLEAN;
DERIVE
Dim  :  IfcDimensionCount :=  BasisSurface.Dim;
END_ENTITY;