Begrenzte Kurve | |

Trimmed Curve | |

Courbe de rognage |

Item | SPF | XML | Change | Description |
---|---|---|---|---|

IFC4 Addendum 1 |
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IfcTrimmedCurve | ||||

SenseAgreement | MODIFIED | Type changed from BOOLEAN to IfcBoolean. | ||

IFC4x2 FINAL |
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IfcTrimmedCurve | ||||

PositioningElement | ADDED |

An IfcTrimmedCurve is a bounded curve that is trimmed at both ends. The trimming points may be provided by
a Cartesian point or by a parameter value, based on the parameterization of the *BasisCurve*. The
*SenseAgreement* attribute indicates whether the direction of the IfcTrimmedCurve agrees with or is
opposed to the direction of the *BasisCurve*.

NOTE In case of theBasisCurvebeing a closed curve, such as an IfcCircle or IfcEllipse, theSenseAgreementaffects the geometric shape of the IfcTrimmedCurve.

Figure 382 — Trimmed curve parameterization |

Figure 382 shows the four arcs (dashed blue and green lines with arrow showing different orientations) that
can be defined by the same *BasisCurve* (of type IfcCircle) and the same trimming points (given by
Cartesian points and parameter values) by using different assignments to *Trim1* and *Trim2* and
*SenseAgreement*.

NOTE Since theBasisCurveis closed (type IfcCircle), the exception of the informal proposition IP3 applies, i.e. the sense flag is not required to be consistent with the parameter values ofTrim1andTrim1, so the rule (sense = parameter 1 < parameter 2) may not be fulfilled.

NOTE Definition according to ISO/CD 10303-42:1992

A trimmed curve is a bounded curve which is created by taking a selected portion, between two identified points, of the associated basis curve. The basis curve itself is unaltered and more than one trimmed curve may reference the same basis curve. Trimming points for the curve may be identified by:

- parametric value
- geometric position
- both of the above
At least one of these shall be specified at each end of the curve. The

SenseAgreementmakes it possible to unambiguously define any segment of a closed curve such as a circle. The combinations of sense and ordered end points make it possible to define four distinct directed segments connecting two different points on a circle or other closed curve. For this purpose cyclic properties of the parameter range are assumed; for example, 370 degrees is equivalent to 10 degrees.The IfcTrimmedCurve has a parameterization which is inherited from the particular basis curve reference. More precisely the parameter s of the trimmed curve is derived from the parameter of the basis curve as follows:

- if
SenseAgreementis TRUE:s = t - t_{1}- if
SenseAgreementis FALSE:s = t_{2}- tIn the above equations t

_{1}is the value given byTrim1or the parameter value corresponding to point 1 and t_{2}is the value given byTrim2or the parameter value corresponding to point 2. The resultant IfcTrimmedCurve has a parameter ranging from 0 at the first trimming point to |t_{2}- t_{1}| at the second trimming point.NOTE In case of a closed curve, it may be necessary to increment t1 or t2 by the parametric length for consistency with the sense flag.

NOTE Entity adapted fromtrimmed_curvedefined in ISO 10303-42

HISTORY New entity in IFC1.0

Informal Propositions:

- Where both the parameter value and the Cartesian point exist for
*Trim1*and*Trim2*they shall be consistent. (i.e., the*BasisCurve*evaluated at the parameter value shall coincide with the specified point). - When a Cartesian point is specified by
*Trim1*or by*Trim2*it shall lie on the*BasisCurve*. - Except the case of a closed
*BasisCurve*where both parameter 1 and parameter 2 exist, they shall be consistent with the sense flag, i.e., (sense = parameter 1 < parameter 2). Or, for every open curve where both parameter 1 and parameter 2 exist, they shall be consistent with the*SenseAgreement*, i.e.,*SenseAgreement*= (parameter 1 < parameter 2). - If both parameter 1 and parameter 2 exist, then parameter 1 <> parameter 2. For a closed base curve, e.g. IfcCircle or IfcEllipse, this also applies to the cyclic properties, as 360' is equal to 0', parameter 1 = 360' and parameter 2 = 0' are treated as being equal and therefore violating this proposition.
- When a parameter value is specified by
*Trim1*or*Trim2*it shall lie within the parametric range of the*BasisCurve*.

# | Attribute | Type | Cardinality | Description | G |
---|---|---|---|---|---|

1 | BasisCurve | IfcCurve | The curve to be trimmed. For curves with multiple representations any parameter values given as Trim1 or Trim2 refer to the master representation of the BasisCurve only. | X | |

2 | Trim1 | IfcTrimmingSelect | S[1:2] | The first trimming point which may be specified as a Cartesian point, as a real parameter or both. | X |

3 | Trim2 | IfcTrimmingSelect | S[1:2] | The second trimming point which may be specified as a Cartesian point, as a real parameter or both. | X |

4 | SenseAgreement | IfcBoolean | Flag to indicate whether the direction of the trimmed curve agrees with or is opposed to the direction of the basis curve. | X | |

5 | MasterRepresentation | IfcTrimmingPreference | Where both parameter and point are present at either end of the curve this indicates the preferred form. | X |

Rule | Description |
---|---|

Trim1ValuesConsistent | Either a single value is specified for Trim1, or the two trimming values are of different type (point and parameter) |

Trim2ValuesConsistent | Either a single value is specified for Trim2, or the two trimming values are of different type (point and parameter) |

NoTrimOfBoundedCurves | Already bounded curves shall not be trimmed. |

# | Attribute | Type | Cardinality | Description | G |
---|---|---|---|---|---|

IfcRepresentationItem | |||||

LayerAssignment | IfcPresentationLayerAssignment @AssignedItems | S[0:1] | Assignment of the representation item to a single or multiple layer(s). The LayerAssignments can override a LayerAssignments of the IfcRepresentation it is used within the list of Items.
IFC2x3 CHANGE The inverse attribute IFC4 CHANGE The inverse attribute | X | |

StyledByItem | IfcStyledItem @Item | S[0:1] | Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve.
IFC2x3 CHANGE The inverse attribute | X | |

IfcGeometricRepresentationItem | |||||

IfcCurve | |||||

Dim :=IfcCurveDim(SELF) | IfcDimensionCount | The space dimensionality of this abstract class, defined differently for all subtypes, i.e. for IfcLine, IfcConic and IfcBoundedCurve. | X | ||

IfcBoundedCurve | |||||

PositioningElement | IfcLinearPositioningElement @Axis | ? | X | ||

IfcTrimmedCurve | |||||

1 | BasisCurve | IfcCurve | The curve to be trimmed. For curves with multiple representations any parameter values given as Trim1 or Trim2 refer to the master representation of the BasisCurve only. | X | |

2 | Trim1 | IfcTrimmingSelect | S[1:2] | The first trimming point which may be specified as a Cartesian point, as a real parameter or both. | X |

3 | Trim2 | IfcTrimmingSelect | S[1:2] | The second trimming point which may be specified as a Cartesian point, as a real parameter or both. | X |

4 | SenseAgreement | IfcBoolean | Flag to indicate whether the direction of the trimmed curve agrees with or is opposed to the direction of the basis curve. | X | |

5 | MasterRepresentation | IfcTrimmingPreference | Where both parameter and point are present at either end of the curve this indicates the preferred form. | X |

` <xs:element name="IfcTrimmedCurve" type="ifc:IfcTrimmedCurve" substitutionGroup="ifc:IfcBoundedCurve" nillable="true"/>`

<xs:complexType name="IfcTrimmedCurve">

<xs:complexContent>

<xs:extension base="ifc:IfcBoundedCurve">

<xs:sequence>

<xs:element name="BasisCurve" type="ifc:IfcCurve" nillable="true"/>

<xs:element name="Trim1">

<xs:complexType>

<xs:group ref="ifc:IfcTrimmingSelect" maxOccurs="2"/>

<xs:attribute ref="ifc:itemType" fixed="ifc:IfcTrimmingSelect"/>

<xs:attribute ref="ifc:cType" fixed="set"/>

<xs:attribute ref="ifc:arraySize" use="optional"/>

</xs:complexType>

</xs:element>

<xs:element name="Trim2">

<xs:complexType>

<xs:group ref="ifc:IfcTrimmingSelect" maxOccurs="2"/>

<xs:attribute ref="ifc:itemType" fixed="ifc:IfcTrimmingSelect"/>

<xs:attribute ref="ifc:cType" fixed="set"/>

<xs:attribute ref="ifc:arraySize" use="optional"/>

</xs:complexType>

</xs:element>

</xs:sequence>

<xs:attribute name="SenseAgreement" type="ifc:IfcBoolean" use="optional"/>

<xs:attribute name="MasterRepresentation" type="ifc:IfcTrimmingPreference" use="optional"/>

</xs:extension>

</xs:complexContent>

</xs:complexType>

```
ENTITY IfcTrimmedCurve
```

SUBTYPE OF (IfcBoundedCurve)**;**

BasisCurve : IfcCurve;

Trim1 : SET [1:2] OF IfcTrimmingSelect;

Trim2 : SET [1:2] OF IfcTrimmingSelect;

SenseAgreement : IfcBoolean;

MasterRepresentation : IfcTrimmingPreference;

WHERE

Trim1ValuesConsistent : (HIINDEX(Trim1) = 1) OR (TYPEOF(Trim1[1]) <> TYPEOF(Trim1[2]));

Trim2ValuesConsistent : (HIINDEX(Trim2) = 1) OR (TYPEOF(Trim2[1]) <> TYPEOF(Trim2[2]));

NoTrimOfBoundedCurves : NOT('IFCGEOMETRYRESOURCE.IfcBoundedCurve' IN TYPEOF(BasisCurve));

END_ENTITY;