IFC4 Addendum 1

BACnet MVD

#### F.2 IFC4 Addendum 1

The first Addendum of the IFC4 release has the main scope to provide documentation improvements, resolve issues that had occurred since the official release of IFC4 in March 2013, and to addresses implementation issues and concerns.

The main change incorporated into IFC4 ADD1 schema is:

- Improvement and simplification of the explicit geometric representation of composite curves: addition of a new geometric item for indexed based poly curves. It requires the addition of the following entities and types:
  - entities IfcIndexedPolyCurve, IfcCartesianPointList2D
  - select type IfcSegmentIndexSelect
  - defined types IfcArcIndex, IfcLineIndex

Minor corrections and improvements to the IFC4 ADD1 schema include:

- Use of defined types throughout the schema, i.e. using IfcInteger instead of , including the addition of IfcBinary
- Use of the new type IfcPositiveInteger to restrict the indices used e.g. for tessellated items to positive, one-based integers
- Adding the missing attribute LongName to IfcBuildingSystem in order to make it consistent with IfcDistributionSystem.
- Promoting the inverse attribute HasCoverings from IfcBuildingElement to IfcElement to enable the inverse navigation also for IfcDistributionElement
- Adding the inverse attribute HasCoordinateOperation to IfcGeometricRepresentationSystem and IfcCoordinateReferenceSystem to enable the inverse navigation to the GIS coordinate transformation
- Making the indespensible Name attribute mandatory at IfcCoordinateReferenceSystem while making the GeodeticDatum optional
- Changing the cardinality of the inverse attribute DefinesOccurrence at IfcPropertySetDefinition to allow property sets to be shared by many such relationships
- Adding the where rule NoCoordOperation to IfcGeometricRepresentationSubContext to prevent the use of conflicting GIS transformations of sub contexts
- Adding the where rule UnboundedSurface to IfcBoxedHalfSpace to prevent the use of bounded surfaces as clipping planes
- Adding the where rule UniquePropertySetNames at IfcObject and IfcTypeObject to enforce property sets attached to a single object to have unique names
- Remove the where rule HasOwnerHistory at IfcProject to enable model views not using owner history information
- Remove the where rule CorrectShapeDecomposition at IfcRamp, IfcRoof, IfcStair to enable model views to determine correct use of geometric shape representations

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