Geometric representation

Version : 001 (18/06/00)

Definition

The concept of 'Geometric representation' describes the method for assigning geometric representations to an object. In theory it is possible to attach any number of different geometric representations to an object, where each object creates its own instance of the 'Geometric representation' concept. I practice we have to agree what type of geometric representation is used with each object type - this is done through the Geometry Use Definitions that are defined in the IFC documentation. In addition to these pre defined representation it is possible to define custom geometry use definitions for specific uses.

The following is a list of all specified geometric representations. This is a subset from all the possibilities in the IFC model. Also other representations can be used, but they have to be used in addition to the ones specified here. As a minimum the bounding box geometry has to be provided with any unspecified geometry type.

Geometry type
Extrusion
Profile
Segments
Clipped
Slanted
 BoundingBox
 Extruded solid  Linear  Rectangular  1  No  No
 Extruded solid  Linear  Circular  1  No  No
 Extruded solid  Linear  Arbitrary  1  No  No
 Extruded solid  Linear  Curved  1  No  No
 Extruded solid  Linear  Rectangular  n  No  No
 Extruded solid  Linear  Circular  n  No  No
 Extruded solid  Linear  Arbitrary  n  No  No
 Extruded solid  Linear  Curved  n  No  No
 Extruded solid  Linear  Rectangular  1  No  Yes
 Extruded solid  Linear  Circular  1  No  Yes
 Extruded solid  Linear  Arbitrary  1  No  Yes
 Extruded solid  Linear  Curved  1  No  Yes
 Extruded solid  Linear  Rectangular  1  Yes  No
 Extruded solid  Linear  Circular  1  Yes  No
 Extruded solid  Linear  Arbitrary  1  Yes  No
 Extruded solid  Linear  Curved  1  Yes  No
 Extruded solid  Linear  Rectangular  1  Yes  Yes
 Extruded solid  Linear  Circular  1  Yes  Yes
 Extruded solid  Linear  Arbitrary  1  Yes  Yes
 Extruded solid  Linear  Curved  1  Yes  Yes
 Extruded solid  Revolved  Rectangular  1  No  No
 Extruded solid  Revolved  Rectangular  1  Yes  No
 Brep
 2D Geometry

The IFC model contains several identification values for geometry, but unfortunately they can't really be used to identify the geometry. On one side the IFC specifications define how some of these identifiers should be used, but those specifications are rather in the way of using the identifiers than helping to use them. On the other hand the R1.5.1 implementations are made such, that using intelligent identifiers is not possible if we want to maintain compatibility with R1.5.1. These are the IAI defined identifiers that should be used for R1.5.1 compatibility

Identifying the geometry we find in an IFC file is important, because the geometry needs to be mapped to a internal representation in the programs. Different types of geometry require a different mapping and the geometry has to be identified in order to use the right mapping in each case. The following is a list of identification values and methods that can be used:

View considerations

Used by views

Data structure

IfcProductDefinitionShape
GlobalId
OwnerHistory
Owner history [all]
ShapeRepresentations
IfcShapeRepresentation
ContextOfItems
IfcGeometricRepresentationContext
GlobalId
ContextIdentifier
ContextType
CoordinateSpaceDimension
RepresentationIdentifier
RepresentationType
Items
2D geometry [1,5]
Bounding box geometry [all]
Brep geometry [3,5]
Extruded solid: arbitrary [all]
Extruded solid: arbitrary, clipped [3,5]
Extruded solid: arbitrary, clipped, slanted [3,5]
Extruded solid: arbitrary, multiple segments [3,5]
Extruded solid: arbitrary, slanted [3,5]
Extruded solid: circular [1,3,5]
Extruded solid: circular, clipped [3,5]
Extruded solid: circular, clipped, slanted [3,5]
Extruded solid: circular, multiple segments [3,5]
Extruded solid: circular, slanted [3,5]
Extruded solid: curved [1,2,3,5]
Extruded solid: curved, clipped [3,5]
Extruded solid: curved, clipped, slanted [3,5]
Extruded solid: curved, multiple segments [3,5]
Extruded solid: curved, slanted [3,5]
Extruded solid: rectangular [1,3,5]
Extruded solid: rectangular, clipped [3,5]
Extruded solid: rectangular, clipped, slanted [3,5]
Extruded solid: rectangular, multiple segments [3,5]
Extruded solid: rectangular, slanted [3,5]
Revolved solid: rectangular [1,3,5]
Revolved solid: rectangular, clipped [3,5]
2D boundary: arbitrary [1,3,5]

Uses concepts

Owner history [all]

Used by concepts

Beam
Cabinet
Column
Counter or shelf
Electrical appliance
Electrical fixture
Floor slab
Flow controller
Flow equipment
Flow fitting
Flow segment
Flow terminal
Furniture
Opening element
Plumbing fixture
Proxy [product with geometry]
Roof slab
Simple door
Simple window
Space
Space boundary
Stair
Wall

Copyright © 2000-2002 BLIS-Project [BLIS, Registered Organization]
Author: Jiri Hietanen (jiri.hietanen@qpartner.com)
All rights reserved.