IfcArcIndex

BACnet MVD

#### IfcArcIndex

Natural language names

Change log

Item | SPF | XML | Change | Description
--- | --- | --- | --- | ---
IFC4 Addendum 1
IfcArcIndex |  |  | ADDED |

##### Semantic definitions at the type

Type definition

The IfcArcIndex describes a single circular arc segment within a poly curve by providing a list on indices. The first index is the start point of the circular arc, the second index is a point on arc, the third index is the end point of the circular arc. The three points shall not be co-linear.

> NOTE The type is used for IfcIndexedPolyCurve to point into an IfcCartesianPointList for providing the Cartesian points of the circular arc segments of the poly curve.

> HISTORY New Type in IFC4 ADD1

Informal Propositions:

1. The second index, resolving to a point on arc, shall resolve into a Cartesian point that has approximately the same distance to the start point and the end point of the circular arc. This is due to avoid numeric instability, if the point on arc is too close to either the start or the end point.

##### Formal representations

XML Specification
`<xs:complexType name="IfcArcIndex">
<xs:simpleContent>
<xs:extension base="ifc:List-IfcArcIndex">
<xs:attribute ref="ifc:itemType" fixed="ifc:IfcPositiveInteger"/>
<xs:attribute ref="ifc:cType" fixed="list"/>
<xs:attribute ref="ifc:arraySize" use="optional"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
<xs:simpleType name="List-IfcArcIndex">
<xs:restriction>
<xs:simpleType>
<xs:list itemType="ifc:IfcPositiveInteger"/>
</xs:simpleType>
<xs:minLength value="3"/>
<xs:maxLength value="3"/>
</xs:restriction>
</xs:simpleType>
`
EXPRESS Specification
`TYPE IfcArcIndex = LIST [3:3] OF IfcPositiveInteger;
END_TYPE;

EXPRESS-G diagram

`

References: IfcSegmentIndexSelect

Link to this page