IFC geometrical concepts

IFC is a standard with a rich set of geometric primitives, with core concepts defined in the geometry, presentation, material, topology and profile resource subschemas. But also outside of these modules, there are various concepts that have geometrical implications such as openings and space boundary relationships in the productextension subschema. This listing below tries to provide a comprehensive overview broken down per the categories below:

Relational; typically IfcRelationship between elements subtypes, but also clearance geometry which is a potential additional shape representation identifier
Product-level; resources applicable the IfcProduct such as material-based styling; openings
Item-level; the individual items that make up representation of the element; which are in turn potentially affected by product-level features such as openings and styling
Context; provides additional information on individual items such as precision, target scale and semantic use of the geometry
Geo-referencing;

Level Concept Notes Related terms from ISO / OGC (SFA, GeoSPARQL, GML, …)

Level	Concept	Notes	Related terms from ISO / OGC (SFA, GeoSPARQL, GML, …)
Relational	Space boundaries (connection geometry)	`IfcRelSpaceBoundary`: Surfaces representing adjacencies between spaces and building elements primarily intended for thermal simulation.	`geof:sfTouches`
Relational	Interferences	`IfcRelInterferesElements`: Primarily intended for modelling clash detection outcomes and over- and underpasses in infrastructure models. Likely has seen little use in practice.	`ST_Intersects`
Relational	Metric constraints	`IfcMetric`: distances, parametric expressions between properties and geometry; supported in the schema (has limitations on indexing into unordered aggregates) and rarely used in practice.	`ST_Distance` `owl:sameAs` `rdfs:seeAlso`
Relational	Clearance geometry	`IfcShapeRepresentation[RepresentationIdentifier='Clearance']`: Dedicated shapes encoding minimum clearances (e.g., around equipment, maintenance envelopes, door swings); a separate representation with its own context
Product	Relative positioning	`IfcLocalPlacement` provides hierarchical local coordinate systems for products. Informal proposition are in place to define a placement hierarchy that follows the project decomposition structure	gml:AffineCS
Product	Linear positioning	`IfcLinearPlacement` provides linear positioning that derives an orientation and positioning frame from a length measure along an (IfcAlignment) curve	ISO 19148:2021
Product	Grid placement	`IfcGridPlacement` provides placement by means of the computed intersection between two grid axes with underlying curve geometry
Product	Openings	`IfcRelVoidsElements` + `IfcOpeningElement`/`IfcVoidingFeature` models a subtractive boolean operation applied to host elements (walls, slabs, etc.); in principle extensible to other feature kinds such as `IfcProjectionElement`. In IFC2X3 CoordinationView these were to be processed by the importer. In IFC4 ReferenceView, in principle, these are precomputed at export time.	`ST_Difference`
Product	Material association	`IfcRelAssociatesMaterial`, layered / list / constituent / profile-based Links product geometry to material models: layered elements, material lists, constituents, profile-based materials. Especially layered materials (IfcMaterialLayerSet[Usage]) have geometric implications because it semantically slices the geometry by means of planes defined from offsets along a reference curve (for vertical elements) or along the extrusion direction.
Product	Parametric geometry as geometry-related semantics via property sets (e.g. `Pset_MechanicalFastenerBolt`, `IfcWindowLiningProperties`)	Semantic parameters that can be used to drive or reconstruct geometry when explicit representations are absent.
Product	Product-level composite curves defining the 'business-logic' of parametric alignment segment nesting within a curve	Decomposition of IfcAlignment into IfcAlignmentSegment with parametric geometry (typically redundant with item-level curves).	OGC LandInfra/InfraGML alignment model
Product	Aggregation of product into assemblies: composition (`IfcElementAssembly`) / nesting (ports, alignment segments)	Product-level aggregation (e.g., ports, sub-elements, segments)
Item	Basic 0D/1D/2D items: points, curves, faces (IfcCartesianPoint, IfcPolyline, IfcCompositeCurve, IfcFace)	Simple representations or underlying points, polylines, composite curves (including circular/arc segments), and faces used in higher-level geometry.	SFA: Point, LineString, MultiLineString, Polygon; GML: gml:Point, gml:Curve, gml:LineString
Item	Profiles: parametric (e.g I shape) / arbitrary / derived / composite (IfcProfileDef, IfcArbitraryProfileDef, IfcDerivedProfileDef, IfcCompositeProfileDef) [Note: not strictly an independent IfcRepresentationItem]	Cross-section definitions used by sweeps and structural members; parametric catalog profiles and arbitrary section shapes.
Item	Annotation geometry: text literals, hatches and fills	`IfcTextLiteral`, `IfcFillAreaStyle` etc. 2D annotation geometry, symbolization and fills; mostly for documentation, not primary 3D model.
Item	Explicit (BRep) representations of 3D faceted solids and surfaces	`IfcFacetedBrep`	SFA: PolyhedralSurface
Item	Explicit (BRep) representations of 3D curved solids and surfaces	Advanced BRep: with (e.g) NURBS faces (IfcAdvancedFace)
Item	Explicit mesh/polyhedron representations (called tessellation)	`IfcTessellatedFaceSet` `IfcTriangulatedFaceSet` `IfcPolygonalFaceSet` Indexed face sets representing triangulated or polygonal surfaces/solids; compact storage via point lists and indices.	SFA: PolyhedralSurface gml:TriangulatedSurface
Item	TIN / surface models	`IfcTriangulatedIrregularNetwork` Specialized tessellated representation for terrain and horizontal surfaces (single f(X,Y)→Z for any X,Y); typical for infrastructure and terrain models.	gml:Tin
Item	Swept / procedural solids: extrusion, revolution, sweeps along curve (disk, arbitrary, fixed reference), sectioned solids and surfaces	3D solids defined by sweeping profiles along vectors or curves: straight/linear extrusions, revolutions, sweeps along curves (swept disk, arbitrary orientation, fixed reference), tapered forms, sectioned solids/surfaces. Note that this is a fairly large category with many items and combinatorial possibilities lumped into one.
Item	Boolean operations (CSG trees)	Solids defined as binary trees combining operands via union, intersection, difference; often nested and require recursive traversal.	SFA: ST_Union, ST_Intersection, ST_Difference
Item	CSG primitives	`IfcCsgPrimitive3D` Are only part of the CSG expressions, but include things like cylinder and sphere which are 'harder' to produce otherwise (as revolutions)
Item	Surface-only geometry for connection / space boundaries and advanced face surfaces (extrusion, revolution, bounded, NURBS)	Surfaces used without explicit solid closure, e.g. for space boundaries or analytical/architectural surfaces.	gml:Surface
Item	Styling by item as a whole (IfcStyledItem, IfcSurfaceStyle, IfcCurveStyle)	Assignment of colors, line styles to geometric items or tessellated faces as a whole
Item	Granular styling by sub-item (IfcSurfaceStyle, IfcIndexedColourMap)	E.g the application of a different color to a face within a shell, or per-face colors in tesselations using IfcIndexedColourMap, or retaining distinct surface styles after applying boolean operations
Item	Styling by item: Textures	`IfcSurfaceStyleWithTextures` and three subtypes of `IfcSurfaceTexture` for a specialization of the above with texture as a binary blob, a compressed inline literal or an external URI reference. The complexity of supporting textures is mostly related to handling and defining texture coordinates (UV) on the procedural geometries (such as sweeps and booleans). Most likely `IfcReparametrisedCompositeCurveSegment` is also intended for supporting textures so that the U space of the profile prior to extrusion can be controlled.
Item	Mapped items / reusable definitions	`IfcMappedItem` and type object occurrences: Instancing and transformations: one definition, multiple placed occurrences with transforms. In IFC2X3 it was not allowed to re-use the full representation as a whole, later in IFC4 that is possible.
Item	(Non-)uniform scaling and mirroring	`IfcMappedItem` is also the only mechanism in IFC that supports scaling and mirroring.
Item	Composite representations (IfcGeometricSet, IfcCompositeProfileDef, multiple shape representation items)	Sets of curves, surfaces, and points combined into a single representation; multi-rep shape representations for one object.	gml:MultiCurve, gml:MultiSurface, gml:CompositeCurve, gml:CompositeSurface
Item	Topological representations for analytical structures	`IfcEdge` `IfcVertex` `IfcFace` `IfcTopologyRepresentation` Explicit topology (vertices, edges, faces) as top-level items; often used in structural/analytical models.
Item	Point clouds and coverages	`IfcShapeRepresentation` + `IfcCartesianPointList3D`
Context	Representation context (IfcGeometricRepresentationContext): identifier, target scale, clearance geometries, subcontexts	Defines modeling context: dimensionality, precision, world coordinate system, true north, representation identifiers; may host clearance contexts.
Context	Tolerance and precision settings	`IfcGeometricRepresentationContext.Precision` Model-level precision and tolerances that influence how geometry is interpreted and when elements are considered coincident. Only linear tolerance, no angular setting and no local (e.g per-vertex) possibilities.
Georeferencing	Local engineering CRS (IfcGeometricRepresentationContext.WorldCoordinateSystem, true north)	Defines the local engineering coordinate system
Georeferencing	Map/projection-based georeferencing incl. vertical reference	`IfcMapConversion`, `IfcProjectedCRS` Conversion from local model coordinates to a map/projected CRS; explicit link to EPSG or other CRS identifiers; since IFC4/IFC4x3.	ISO 19111 referencing by coordinates and transformations; SFA: SRID on geometries.
Georeferencing	Postal address	`IfcPostalAddress`, `Pset_Address`
Georeferencing	IfcSite reference coordinates	`IfcSite` has DMS reference coords for latitude and longitude

Relational

Space boundaries (connection geometry)

IfcRelSpaceBoundary: Surfaces representing adjacencies between spaces and building elements primarily intended for thermal simulation.

geof:sfTouches

Relational

Interferences

IfcRelInterferesElements: Primarily intended for modelling clash detection outcomes and over- and underpasses in infrastructure models. Likely has seen little use in practice.

ST_Intersects

Relational

Metric constraints

IfcMetric: distances, parametric expressions between properties and geometry; supported in the schema (has limitations on indexing into unordered aggregates) and rarely used in practice.

ST_Distance owl:sameAs rdfs:seeAlso

Relational

Clearance geometry

IfcShapeRepresentation[RepresentationIdentifier='Clearance']: Dedicated shapes encoding minimum clearances (e.g., around equipment, maintenance envelopes, door swings); a separate representation with its own context

Product

Relative positioning

IfcLocalPlacement provides hierarchical local coordinate systems for products. Informal proposition are in place to define a placement hierarchy that follows the project decomposition structure

gml:AffineCS

Product

Linear positioning

IfcLinearPlacement provides linear positioning that derives an orientation and positioning frame from a length measure along an (IfcAlignment) curve

ISO 19148:2021

Product

Grid placement

IfcGridPlacement provides placement by means of the computed intersection between two grid axes with underlying curve geometry

Product

Openings

IfcRelVoidsElements + IfcOpeningElement/IfcVoidingFeature models a subtractive boolean operation applied to host elements (walls, slabs, etc.); in principle extensible to other feature kinds such as IfcProjectionElement. In IFC2X3 CoordinationView these were to be processed by the importer. In IFC4 ReferenceView, in principle, these are precomputed at export time.

ST_Difference

Product

Material association

IfcRelAssociatesMaterial, layered / list / constituent / profile-based Links product geometry to material models: layered elements, material lists, constituents, profile-based materials. Especially layered materials (IfcMaterialLayerSet[Usage]) have geometric implications because it semantically slices the geometry by means of planes defined from offsets along a reference curve (for vertical elements) or along the extrusion direction.

Product

Parametric geometry as geometry-related semantics via property sets (e.g. Pset_MechanicalFastenerBolt, IfcWindowLiningProperties)

Semantic parameters that can be used to drive or reconstruct geometry when explicit representations are absent.

Product

Product-level composite curves defining the 'business-logic' of parametric alignment segment nesting within a curve

Decomposition of IfcAlignment into IfcAlignmentSegment with parametric geometry (typically redundant with item-level curves).

OGC LandInfra/InfraGML alignment model

Product

Aggregation of product into assemblies: composition (IfcElementAssembly) / nesting (ports, alignment segments)

Product-level aggregation (e.g., ports, sub-elements, segments)

Item

Basic 0D/1D/2D items: points, curves, faces (IfcCartesianPoint, IfcPolyline, IfcCompositeCurve, IfcFace)

Simple representations or underlying points, polylines, composite curves (including circular/arc segments), and faces used in higher-level geometry.

SFA: Point, LineString, MultiLineString, Polygon; GML: gml:Point, gml:Curve, gml:LineString

Item

Profiles: parametric (e.g I shape) / arbitrary / derived / composite (IfcProfileDef, IfcArbitraryProfileDef, IfcDerivedProfileDef, IfcCompositeProfileDef) [Note: not strictly an independent IfcRepresentationItem]

Cross-section definitions used by sweeps and structural members; parametric catalog profiles and arbitrary section shapes.

Item

Annotation geometry: text literals, hatches and fills

IfcTextLiteral, IfcFillAreaStyle etc. 2D annotation geometry, symbolization and fills; mostly for documentation, not primary 3D model.

Item

Explicit (BRep) representations of 3D faceted solids and surfaces

IfcFacetedBrep

SFA: PolyhedralSurface

Item

Explicit (BRep) representations of 3D curved solids and surfaces

Advanced BRep: with (e.g) NURBS faces (IfcAdvancedFace)

Item

Explicit mesh/polyhedron representations (called tessellation)

IfcTessellatedFaceSet IfcTriangulatedFaceSet IfcPolygonalFaceSet Indexed face sets representing triangulated or polygonal surfaces/solids; compact storage via point lists and indices.

SFA: PolyhedralSurface gml:TriangulatedSurface

Item

TIN / surface models

IfcTriangulatedIrregularNetwork Specialized tessellated representation for terrain and horizontal surfaces (single f(X,Y)→Z for any X,Y); typical for infrastructure and terrain models.

gml:Tin

Item

Swept / procedural solids: extrusion, revolution, sweeps along curve (disk, arbitrary, fixed reference), sectioned solids and surfaces

3D solids defined by sweeping profiles along vectors or curves: straight/linear extrusions, revolutions, sweeps along curves (swept disk, arbitrary orientation, fixed reference), tapered forms, sectioned solids/surfaces. Note that this is a fairly large category with many items and combinatorial possibilities lumped into one.

Item

Boolean operations (CSG trees)

Solids defined as binary trees combining operands via union, intersection, difference; often nested and require recursive traversal.

SFA: ST_Union, ST_Intersection, ST_Difference

Item

CSG primitives

IfcCsgPrimitive3D Are only part of the CSG expressions, but include things like cylinder and sphere which are 'harder' to produce otherwise (as revolutions)

Item

Surface-only geometry for connection / space boundaries and advanced face surfaces (extrusion, revolution, bounded, NURBS)

Surfaces used without explicit solid closure, e.g. for space boundaries or analytical/architectural surfaces.

gml:Surface

Item

Styling by item as a whole (IfcStyledItem, IfcSurfaceStyle, IfcCurveStyle)

Assignment of colors, line styles to geometric items or tessellated faces as a whole

Item

Granular styling by sub-item (IfcSurfaceStyle, IfcIndexedColourMap)

E.g the application of a different color to a face within a shell, or per-face colors in tesselations using IfcIndexedColourMap, or retaining distinct surface styles after applying boolean operations

Item

Styling by item: Textures

IfcSurfaceStyleWithTextures and three subtypes of IfcSurfaceTexture for a specialization of the above with texture as a binary blob, a compressed inline literal or an external URI reference. The complexity of supporting textures is mostly related to handling and defining texture coordinates (UV) on the procedural geometries (such as sweeps and booleans). Most likely IfcReparametrisedCompositeCurveSegment is also intended for supporting textures so that the U space of the profile prior to extrusion can be controlled.

Item

Mapped items / reusable definitions

IfcMappedItem and type object occurrences: Instancing and transformations: one definition, multiple placed occurrences with transforms. In IFC2X3 it was not allowed to re-use the full representation as a whole, later in IFC4 that is possible.

Item

(Non-)uniform scaling and mirroring

IfcMappedItem is also the only mechanism in IFC that supports scaling and mirroring.

Item

Composite representations (IfcGeometricSet, IfcCompositeProfileDef, multiple shape representation items)

Sets of curves, surfaces, and points combined into a single representation; multi-rep shape representations for one object.

gml:MultiCurve, gml:MultiSurface, gml:CompositeCurve, gml:CompositeSurface

Item

Topological representations for analytical structures

IfcEdge IfcVertex IfcFace IfcTopologyRepresentation Explicit topology (vertices, edges, faces) as top-level items; often used in structural/analytical models.

Item

Point clouds and coverages

IfcShapeRepresentation + IfcCartesianPointList3D

Context

Representation context (IfcGeometricRepresentationContext): identifier, target scale, clearance geometries, subcontexts

Defines modeling context: dimensionality, precision, world coordinate system, true north, representation identifiers; may host clearance contexts.

Context

Tolerance and precision settings

IfcGeometricRepresentationContext.Precision Model-level precision and tolerances that influence how geometry is interpreted and when elements are considered coincident. Only linear tolerance, no angular setting and no local (e.g per-vertex) possibilities.

Georeferencing

Local engineering CRS (IfcGeometricRepresentationContext.WorldCoordinateSystem, true north)

Defines the local engineering coordinate system

Georeferencing

Map/projection-based georeferencing incl. vertical reference

IfcMapConversion, IfcProjectedCRS Conversion from local model coordinates to a map/projected CRS; explicit link to EPSG or other CRS identifiers; since IFC4/IFC4x3.

ISO 19111 referencing by coordinates and transformations; SFA: SRID on geometries.

Georeferencing

Postal address

IfcPostalAddress, Pset_Address

Georeferencing

IfcSite reference coordinates

IfcSite has DMS reference coords for latitude and longitude