Index Page
EXPRESS Definition |
EXPRESS-G Diagram |
IDL Definition |
This part of the Industry Foundation Classes specifies the resources for the geometric and topological representation of the shape of a product. The specifications within the IfcGeometryResource include:
The explicit geometric and topological representation of the shape is defined following an adaptation of the ISO/CD 10303-42:1992, Industrial Automation Systems and Integration: Product Data Representation and Exchange – Part 42: Integrated Generic Resources. Geometric and Topological Representation. The type, class, and function semantic definition sections follow the adapted wording of the working draft, which is clearly indicated and quoted at each reference. The definitions on explicit geometric and topological representation are explicitly excluded from the copyright of the International Alliance of Interoperability
For more information on the definitions as defined in the formal ISO standard please refer to: ISO/IS 10303-42:1994, Industrial Automation Systems and Integration: Product Data Representation and Exchange – Part 42: Integrated Generic Resources. Geometric and Topological Representation. The formal standard can be obtained through the local publishers of standards in each individual country.
The following is within the scope of the explicit geometric and topological representation in IFC Release 1.5.1:
In Geometry:
In Topology:
In Geometric Shape Models:
The attribute driven representation of standard shapes and shape characteristics is defined as the IFC enhancement of the geometry resource. It provides the definition of standard shapes, like extruded area segments or revolved area segments, and characteristics, in particular for the profile and path used within sweep operations to create solid models. The attributes of standard shape characteristics will later be linked to the semantic property definition of the product, so that the product's shape properties will drive the creation of the appropriate shape representation.
The following is within the scope of the attribute driven representation in IFC Release 1.5.1:
In Attribute Driven Geometric Shape Models:
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: A dimension count is a positive integer used to define the coordinate space dimensionality.
NOTE: Corresponding STEP type: dimension_count, please refer to ISO/IS 10303-42:1994, p. 14 for the final definition of the formal standard. Formal Propositions:
WR1 |
The dimension count should be an integer between 1 and 3 NOTE: This is a further constraint by IFC, the upper limit does not exist in STEP |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: This type defines the three Boolean operators used in the definition of CSG solids.
NOTE: Corresponding STEP type: boolean_operator, please refer to ISO/IS 10303-42:1994, p.167 for the final definition of the formal standard.
NOTE: New Type in IFC Release 1.5.1
ISSUE: See I-330 for changes made in IFC Release 1.5.1 Enumeration:
Union |
The operation of constructing the regularized set theoretic union of the volumes defined by two solids. |
Difference |
The operation of constructing the regularized set theoretic intersection of the volumes defined by two solids. |
Intersection |
The set theoretic difference between volumes defined by two solids. |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: This type conveys the continuity properties of a composite curve or surface. The continuity referred to is geometric, not parametric continuity. For example, in ContSameGradient the tangent vectors of successive segments will have the same direction, but may have different magnitude.
NOTE: Corresponding STEP type: transition_code, please refer to ISO/IS 10303-42:1994, p. 14 for the final definition of the formal standard. Enumeration:
Discontinuous |
The segments do not join. This is permitted only at the boundary of the curve or surface to indicate that it is not closed. |
Continuous |
The segments join but no condition on their tangents is implied. |
ContSameGradient |
The segments join and their tangent vectors or tangent planes are parallel and have the same direction at the joint: equality of derivatives is not required. |
ContSameGradientSameCurvature |
For a curve, the segments join, their tangent vectors are parallel and in the same direction and their curvatures are equal at the joint: equality of derivatives is not required. For a surface this implies that the principle curvatures are the same and the principle directions are coincident along the common boundary. |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: This type is used to describe the preferred way of trimming a parametric curve where the trimming is multiply defined.
NOTE: Corresponding STEP type: trimming_preference, please refer to ISO/IS 10303-42:1994, p. 18 for the final definition of the formal standard. Enumeration:
Cartesian |
Indicates that trimming by Cartesian point is preferred. |
Parameter |
Indicates the preference for the parameter value. |
Unspecified |
Indicates that no preference is communicated. |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: This select type collects together both versions of the placement as used in two dimensional or in three dimensional Cartesian space. This enables entities requiring this information to reference them without specifying the space dimensionality.
NOTE: Corresponding STEP type: axis2_placement, please refer to ISO/IS 10303-42:1994, p. 19 for the final definition of the formal standard.
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: This select type identifies all those types of entities which may participate in a Boolean operation to form a CSG solid.
Definition from IAI: In the current IFC Release 1.5.1 only Boolean results (IfcBooleanResult), half space solids (IfcHalfSpaceSolid), faceted B-Rep, extruded solids and revolved solids (IfcSolidModel) are defined for being valid Boolean operands. CSG primitives are out of scope for the current IFC Release 1.5.1
NOTE: Corresponding STEP type: boolean_operand, please refer to ISO/IS 10303-42:1994, p.167 for the final definition of the formal standard.
NOTE: New Type in IFC Release 1.5.1
ISSUE: See I-330 for changes made in IFC Release 1.5.1
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: This type identifies the types of entity which may be selected as the root of a CSG tree including a single CSG primitive as a special case (not in IFC1.5).
Definition from IAI: In the current IFC Release 1.5.1 only Boolean result (IfcBooleanResult) is defined for being a root tree expression (at IfcCsgSolid). CSG primitives are out of scope for the current IFC Release 1.5.1
NOTE: Corresponding STEP type: csg_select, please refer to ISO/IS 10303-42:1994, p.168 for the final definition of the formal standard.
NOTE: New Type in IFC Release 1.5.1
ISSUE: See I-330 for changes made in IFC Release 1.5.1
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: This select type identifies the two possible ways of trimming a parametric curve; by a Cartesian point on the curve, or by a REAL number defining a parameter value within the parametric range of the curve.
NOTE: Corresponding STEP type: trimming_select, please refer to ISO/IS 10303-42:1994, p. 20 for the final definition of the formal standard.
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: This type is used to identify the types of entity which can participate in vector computations.
NOTE: Corresponding STEP type: vector_or_direction, please refer to ISO/IS 10303-42:1994, p. 20 for the final definition of the formal standard.
EXPRESS Definition
The enumeration defines whether the attribute driven definition of a profile shape shall be geometrically resolved into a curve or into a surface.
Enumeration:
Curve |
The resulting geometric item is of type IfcBoundedCurve and being closed. The resulting swept solid will then define only the bounding surfaces. This can be used to define shapes with thin sheets, such as ducts, where the thickness is not appropriate for geometric representation. |
Area |
The resulting geometric item is of type IfcCurveBoundedPlane. The resulting swept solid will be a three-dimensional body with defined volume. |
NOTE: New type in IFC Release 1.5.
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: The direction and location in three dimensional space of a single axis. An IfcAxis1Placement is defined in terms of a locating point (inherited from IfcPlacement supertype) and an axis direction: this is either the direction of Axis or defaults to (0.0,0.0,1.0). The actual direction for the axis placement is given by the derived attribute Z.
NOTE: New entity in IFC Release 1.5, Corresponding STEP name: axis1_placement, please refer to ISO/IS 10303-42:1994, p. 28 for the final definition of the formal standard.
ISSUE: See issue I-008 for changes made in IFC Release 1.5.
See issues I-332, I-344 for changes made in IFC Release 1.5.1
Example
|
Definition of the IfcAxis1Placement within the three-dimensional coordinate system. |
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
OPT |
Axis |
The direction of the local Z axis |
n/a |
n/a |
NIL |
|
DER |
Z |
The normalized direction of the local Z axis. It is either identical with the Axis value, if given, or it defaults to [0.,0.,1.] |
n/a |
n/a |
(0.,0.,1.) |
Formal Propositions:
WR1 |
The Axis when given should only reference a three-dimensional IfcDirection |
WR2 |
The Cartesian point defining the Location shall have the dimensionality of 3. |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: The location and orientation in two dimensional space of two mutually perpendicular axes. An IfcAxis2Placement2D is defined in terms of a point, (inherited from the IfcPlacement supertype), and an axis. It can be used to locate and originate an object in two dimensional space and to define a Placement Coordinate System. The class includes a point which forms the origin of the Placement Coordinate System. A direction vector is required to complete the definition of the Placement Coordinate System. The reference direction defines the placement X axis direction, the placement Y axis is derived from this.
Definition from IAI: If the RefDirection attribute is not given, the placement defaults to P[1] (x-axis) as [1.,0.] and P[2] (y-axis) as [0.,1.].
NOTE: New entity in IFC Release 1.5, the IFC Release 1.0 entity IfcPlacement_2D was using two normalized and orthogonal axes. This definition is replaced in IFC Release 1.5 by the STEP definition of axis placement. Corresponding STEP name: axis2_placement_2d, please refer to ISO/IS 10303-42:1994, p. 28 for the final definition of the formal standard.
ISSUE: See issue I-008 for changes
made in IFC Release 1.5.
See issues I-332, I-344 for changes
made in IFC Release 1.5.1
|
Definition of the IfcAxis2Placement2D within the two-dimensional coordinate system. |
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
OPT |
RefDirection |
The direction used to determine the direction of the local X Axis |
n/a |
n/a |
NIL |
|
DER |
P |
P[1]: The normalized direction of the placement X Axis. This is (1.0,0.0,0.0) if RefDirection is omitted. P[2]: The normalized direction of the placement Y Axis. This is a derived attribute and is orthogonal to P[1]. |
LIST[2:2] IfcDirection |
n/a |
n/a |
(1.,0.) (0.,1.) |
Formal Propositions:
WR1 |
The Axis when given should only reference a two-dimensional IfcDirection |
WR2 |
The Cartesian point defining the Location shall have the dimensionality of 2. |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: The location and orientation in three dimensional space of three mutually perpendicular axes. An IfcAxis2Placement3D is defined in terms of a point (inherited from IfcPlacement supertype) and two (ideally orthogonal) axes. It can be used to locate and originate an object in three dimensional space and to define a Placement Coordinate System. The class includes a point which forms the origin of the Placement Coordinate System. Two direction vectors are required to complete the definition of the Placement Coordinate System. The Axis is the placement Z axis direction and the RefDirection is an approximation to the placement X axis direction.
Definition from IAI: If the attribute values for Axis and RefDirection are not given, the placement defaults to P[1] (x-axis) as [1.,0.,0.], P[2] (y-axis) as [0.,1.,0.] and P[3] (z-axis) as [0.,0.,1.]
NOTE: New entity in IFC Release 1.5, the IFC Release 1.0 entity IfcPlacement_3D was using three normalized and orthogonal axes. This definition is replaced in IFC Release 1.5 by the STEP definition of axis placement. Corresponding STEP name: axis2_placement_3d, please refer to ISO/IS 10303-42:1994 for the final definition of the formal standard. The WR5 is added.
ISSUE: See issues I-008, I-311 for
changes made in IFC Release 1.5.
See issue I-332 for changes made
in IFC Release 1.5.1
|
Definition of the IfcAxis2Placement3D within the three-dimensional coordinate system. |
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
OPT |
Axis |
The exact direction of the local Z Axis |
n/a |
n/a |
NIL |
|
OPT |
RefDirection |
The direction used to determine the direction of the local X Axis. If necessary an adjustment is made to maintain orthogonality to the Axis direction. If Axis and/or RefDirection is omitted, these directions are taken from the geometric coordinate system. |
n/a |
n/a |
NIL |
|
DER |
P |
The normalized directions of the placement X Axis (P[1]) and the placement Y Axis (P[2]) and the placement Z Axis (P[3]) |
LIST[3:3] IfcDirection |
n/a |
n/a |
(1.,0.,0.) (0.,1.,0.) (1.,0.,0.) |
Formal Propositions:
WR1 |
The dimensionality of the placement location shall be 3 |
WR2 |
The Axis when given should only reference a three-dimensional IfcDirection |
WR3 |
The RefDirection when given should only reference a three-dimensional IfcDirection |
WR4 |
The Axis and RefDirection shall not be parallel or anti-parallel |
WR5 |
Either both (Axis and RefDirection) are not given and therefore defaulted, or both shall be given. This is a further constraint in IFC Release 1.5. |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: A Boolean result is the result of a regularized operation on two solids to create a new solid. Valid operations are regularized union, regularized intersection, and regularized difference. For purpose of Boolean operations, a solid is considered to be a regularized set of points. The final Boolean result depends upon the operation and the two operands. In the case of the difference operator the order of the operands is also significant. The operator can be either union, intersection or difference. The effect of these operators is described below:
NOTE: Corresponding STEP entity: boolean_result. The derived attribute Dim has been added at this level and was therefore demoted from the geometric_representation_item. Please refer to ISO/IS 10303-42:1994, p.175 for the final definition of the formal standard.
NOTE: New Type in IFC Release 1.5.1
ISSUE: See I-330 for changes made in IFC Release 1.5.1
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
Operator |
The Boolean operator used in the operation to create the result. |
Union |
Intersection |
Union |
|
|
FirstOperand |
The first operand to be operated upon by the Boolean operation. |
n/a |
n/a |
n/a |
|
|
SecondOperand |
The second operand specified for the operation. |
n/a |
n/a |
n/a |
|
DER |
Dim |
The space dimensionality of this entity. |
2 |
3 |
3 |
Formal Propositions:
WR1 |
The dimensionality of the first operand shall be the same as the dimensionality of the second operand. |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: A bounded curve is a curve of finite arc length with identifiable end points.
NOTE: Corresponding STEP name: bounded_curve, only the following subtypes have been incorporated into IFC: polyline as IfcPolyline, trimmed_curve as IfcTrimmedCurve, composite_curve as IfcCompositeCurve. The derived attribute Dim has been added at this level and was therefore demoted from the geometric_representation_item. Please refer to ISO/IS 10303-42:1994, p. 44 for the final definition of the formal standard.
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
DER |
Dim |
The space dimensionality of this class, defined differently for all subtypes |
2 |
3 |
3 |
Informal Propositions:
IP1 |
A bounded curve has finite arc length. |
IP2 |
A bounded curve has a start point and an end point. |
EXPRESS Definition
Definition from IAI: Every semantic object showing a physical extent will have a minimum default representation of a bounding box. The bounding box is the one representation that will always exist and be available. Even if more specific representations are associated with an object, the IfcBoundingBox should be updated and made consistent so that applications which may only want this minimal representation will have a valid view of the object geometry.
The general purpose bounding box is therefore used as minimal geometric representation for any geometrically represented object. Represents the minimal box which fully combines said object. ISSUE: See issue I-021 for changes made in IFC Release 1.5. Example
|
The IfcBoundingBox is defined with an own location which can be used to place the IfcBoundingBox relative to the local coordinate system, given by the IfcLocalPlacement Class. The IfcBoundingBox is defined by the lower left corner (Corner) and the upper right corner (XDim, YDim, ZDim measured within the parent co-ordinate system). |
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
Corner |
Location of the bottom left corner (having the minimum values). |
see type |
see type |
[0.,0.,0.] |
|
|
XDim |
Length attribute (measured along the edge parallel to the X Axis) |
0 |
see type |
1 |
|
|
YDim |
Width attribute (measured along the edge parallel to the Y Axis) |
0 |
see type |
1 |
|
|
ZDim |
Height attribute (measured along the edge parallel to the Z Axis) |
0 |
see type |
1 |
|
DER |
Dim |
The space dimensionality of this class |
3 |
3 |
3 |
No formal and informal propositions defined at this level.
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: This entity is a subtype of the half space solid which is trimmed by a surrounding rectangular box. The box has its edges parallel to the coordinate axes of the geometric coordinate system.
NOTE: Corresponding STEP entity : boxed_half_space, please refer to ISO/IS 10303-42:1994, p. 185 for the final definition of the formal standard. The IFC class IfcBoundingBox is used for the definition of the enclosure, providing the same definition as box_domain.
NOTE: New Type in IFC Release 1.5.1
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
Enclosure |
The box which bounds the half space for computational purposes only |
see type |
see type |
- |
Formal Propositions:
WR1 |
The BaseSurface defining the half space shall not be a bounded surface. |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: A point defined by its coordinates in a two or three dimensional rectangular Cartesian coordinate system, or in a two dimensional parameter space. The class is defined in a two or three dimensional space.
NOTE: Corresponding STEP entity : cartesian_point, please refer to ISO/IS 10303-42:1994, p. 23 for the final definition of the formal standard. The derived attribute Dim has been added at this level and was therefore demoted from the geometric_representation_item. The WR1 was added to constrain the usage of IfcCartesianPoint in the context of IFC Geometry. For the purpose of defining geometry in IFC only two and three dimensional Cartesian points are used. This complies to the Note in ISO/IS 10303-42:1994.
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
Coordinates |
The first, second, and third coordinate of the point location. If placed in a two or three dimensional rectangular Cartesian coordinate system, Coordinates[1] is the X coordinate, Coordinates[2] is the Y coordinate, and Coordinates[3] is the Z coordinate. |
LIST[1:3] IfcLengthMeasure |
see type |
see type |
(0.,0.,0.) |
DER |
Dim |
The space dimensionality of this class, determined by the number of coordinates in the List of Coordinates. |
2 |
3 |
3 |
Formal Propositions:
WR1 |
Only two or three dimensional points shall be used for the purpose of defining geometry in this IFC Resource. |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: An IfcCircle is defined by a radius and the location and orientation of the circle. Interpretation of data should be as follows: C = SELF\IfcConic.Position.Location
x = SELF\IfcConic.Position.P[1]
y = SELF\IfcConic.Position.P[2]
z = SELF\IfcConic.Position.P[3]
R = Radius and the circle is parameterized as
The parameterization range is 0 £ u £ 2p (or 0 £ u £ 360 degree). In the placement coordinate system defined above, the circle is the equation C = 0, where
The positive sense of the circle at any point is in the tangent direction, T, to the curve at the point, where
A circular arc is defined by using the IfcTrimmedCurve entity in conjunction with the IfcCircle entity as the BasisCurve.
NOTE: Corresponding STEP entity: circle, please refer to ISO/IS 10303-42:1994, p. 38 for the final definition of the formal standard.
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
Radius |
The radius of the circle, which shall be greater than zero |
see type |
see type |
1 |
No formal and informal propositions defined at this level.
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: A closed shell is a shell of the dimensionality 2 which typically serves as a bound for a region in R3. A closed shell has no boundary, and has non-zero finite extent. If the shell has a domain with coordinate space R3, it divides that space into two connected regions, one finite and the other infinite. In this case, the topological normal of the shell is defined as being directed from the finite to the infinite region.
The shell is represented by a collection of faces. The domain of the shell, if present, contains all those faces, together with their bounds. Associated with each face in the shell is a logical value which indicates whether the face normal agrees with (TRUE) or is opposed to (FALSE) the shell normal. The logical value can be applied directly as a BOOLEAN attribute of an oriented face, or be defaulted to TRUE if the shell boundary attribute member is a face without the orientation attribute.
Definition from IAI: In the current IFC Release 1.5 only poly loops (IfcPolyLoop) are defined for Bounds of face bound (IfcFaceBound). This will allow for faceted B-rep only.
NOTE: Corresponding STEP entity: closed_shell, please refer to ISO/IS 10303-42:1994, p.149 for the final definition of the formal standard.
No attributes and no formal propositions defined at this level.
Informal Propositions:
IP1 |
Every edge shall be referenced exactly twice by the loops of the face. |
IP2 |
Each oriented edge shall be unique. |
IP3 |
No edge shall be referenced by more than two faces. |
IP4 |
Distinct faces of the shell do not intersect, but may share edges or vertices. |
IP5 |
Distinct edges do not intersect but may share vertices. |
IP6 |
Each face reference shall be unique. |
IP7 |
The loops of the shell shall not be a mixture of poly loop and other loop types. Note: this is given, since only poly loop is defined as face bound definition. |
IP8 |
The closed shell shall be an oriented arcwise connected 2-manifold. |
IP9 |
The Euler equation shall be satisfied. Note: Please refer to ISO/IS 10303-42:1994, p.149 for the equation. |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: An IfcCompositeCurve is a collection of curves joined end-to-end. The individual segments of the curve are themselves defined as IfcCompositeCurveSegment. The parameterization of the composite curve is an accumulation of the parametric ranges of the referenced bounded curves. The first segment is parameterized from 0 to l1, and, for i ³ 2, the ith segment is parameterized from
where lk is the parametric length (i.e., difference between maximum and minimum parameter values) of the curve underlying the kth segment.
NOTE: Corresponding STEP entity: composite_curve, please refer to ISO/IS 10303-42:1994, p. 56 for the final definition of the formal standard. The WR2 is added to ensure consistent Dim at all segments.
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
Segments |
The component bounded curves, their transitions and senses. The transition attribute for the last segment defines the transition between the end of the last segment and the start of the first; this transition attribute may take the value discontinuous, which indicates an open curve. |
List [1:N] IfcCompositeCurveSegment |
1 |
N |
1 |
|
SelfIntersect |
Indication of whether the curve intersects itself or not; this is for information only. |
LOGICAL |
see type |
see type |
FALSE |
DER |
NSegments |
The number of component curves. |
INTEGER |
1 |
see type |
1 |
DER |
ClosedCurve |
Indication whether the curve is closed or not; this is derived from the transition code of the last segment. |
LOGICAL |
see type |
see type |
TRUE |
Formal Propositions:
WR1 |
No transition code should be Discontinuous, except for the last code of an open curve. |
WR2 |
Ensures, that all segments used in the curve have the same dimensionality. |
Informal Propositions:
IP1 |
The SameSense attribute of each segment correctly specifies the senses of the component curves. When traversed in the direction indicated by SameSense, the segments shall join end-to-end. |
EXPRESS Definition
Definition from IAI: An Ifc2DCompositeCurve is an IfcCompositeCurve that is defined within the coordinate space of an IfcPlane. Therefore the dimensionality of the Ifc2DCompositeCurve has to be 2.
NOTE: New class in IFC Release 1.5, this class has been introduced to get a more straight forward definition of surface boundaries that its counterpart in STEP: composite_curve_on_surface and boundary_curve. Since the only basis elementary surface in IFC1.5 is the plane surface, a two dimensional composite curve provides enough capability to define the boundary.
No attributes defined at this level.
Formal Propositions:
WR1 |
The composite curve shall be closed. |
WR2 |
The dimensionality of the composite curve shall be 2 |
Class IfcCompositeCurveSegment
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: An IfcCompositeCurveSegment is a bounded curve together with transition information which is used to construct an IfcCompositeCurve.
NOTE: Corresponding STEP entity: composite_curve_segment. The derived attribute Dim has been added at this level. Please refer to ISO/IS 10303-42:1994, p. 57 for the final definition of the formal standard.
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
Transition |
The state of transition (i.e., geometric continuity from the last point of this segment to the first point of the next segment) in a composite curve. |
Dis continuous |
Cont SameGradient SameCurvature |
Continuous |
|
|
SameSense |
An indicator of whether or not the sense of the segment agrees with, or opposes, that of the parent curve. If SameSense is false, the point with highest parameter value is taken as the first point of the segment. |
BOOLEAN |
see type |
see type |
TRUE |
|
ParentCurve |
The bounded curve which defines the geometry of the segment. |
n/a |
n/a |
n/a |
|
DER |
Dim |
The space dimensionality of this class, defined by the dimensionality of the first ParentCurve |
2 |
3 |
3 |
|
INV |
UsingCurves |
The set of composite curves which use this composite curve segment as a segment. This set shall not be empty. |
BAG[1:?] IfcCompositeCurve |
1 |
N |
1 |
Formal Propositions:
WR1 |
The parent curve shall be a bounded curve. |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: An IfcConic is a planar curve which could be produced by intersecting a plane with a cone. A conic is defined in terms of its intrinsic geometric properties rather than being described in terms of other geometry. A conic class always has a Placement Coordinate System defined by a two or three dimensional placement. The parametric representation is defined in terms of this Placement Coordinate System.
NOTE: Corresponding STEP entity: conic, only the following subtypes have been incorporated into IFC 1.5: circle as IfcCircle, ellipse as IfcEllipse. The derived attribute Dim has been added at this level and was therefore demoted from the geometric_representation_item. Please refer to ISO/IS 10303-42:1994, p. 38 for the final definition of the formal standard.
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
Position |
The location and orientation of the conic. |
n/a |
n/a |
n/a |
|
DER |
Dim |
The space dimensionality of this class, defined by the dimensionality of the IfcAxis2Placement |
2 |
3 |
3 |
No formal propositions defined at this level.
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: An IfcConnectedFaceSet is a set of IfcFace such that the domain of faces together with their bounding edges and vertices is connected.
NOTE: Corresponding STEP entity: connected_face_set, only the subtype closed_shell is included as IfcClosedShell. Please refer to ISO/IS 10303-42:1994, p. 144 for the final definition of the formal standard.
ISSUE: See issue I-227 for changes made in IFC Release 1.5.
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
CfsFaces |
The set of faces arcwise connected along common edges or vertices. |
SET[1:?] IfcFace |
1 |
N |
1 |
No formal propositions defined at this level
Informal Propositions:
IP1 |
The union of the domains of the faces and their bounding loops shall be arcwise connected.
|
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: A solid represented as a CSG model is defined by a collection of so-called primitive solids, combined using regularized Boolean operations. The allowed operations are intersection, union, and difference. As a special case a CSG solid can also consists of a single CSG primitive (not in IFC1.5). A CSG solid requires two kinds of information for its complete definition: geometric and structural:
Definition from IAI: The following primitive volumes can be parts of the CSG tree: solid models, i.e. faceted B-Rep (IfcFacetedBrep, IfcFacetedBrepWithVoids) or swept area solid (IfcExtrudedAreaSolid, IfcRevolvedAreaSolid). CSG primitives are out of scope for current IFC Release 1.5.1
NOTE: Corresponding STEP entity: csg_solid, please refer to ISO/IS 10303-42:1994, p.174 for the final definition of the formal standard.
ISSUE: New Type in IFC Release 1.5.1
See I-330 for changes made in IFC
Release 1.5.1
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
TreeRootExpression |
Boolean expression of regularized operators describing the solid. The root of the tree of Boolean expressions is given explicitly as an IfcBooleanResult (the only item in the Select IfcCsgSelect). |
1 |
1 |
1 |
No formal or informal propositions defined at this level.
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: A curve can be envisioned as the path of a point moving in its coordinate space.
NOTE: Corresponding STEP entity: curve, only the following subtypes have been incorporated into IFC 1.5: line as IfcLine, conic as IfcConic, bounded_curve as IfcBoundedCurve. Please refer to ISO/IS 10303-42:1994, p. 37 for the final definition of the formal standard.
No attributes and no formal propositions defined at this level.
Informal Propositions:
IP1 |
A curve shall be arcwise connected. |
IP2 |
A curve shall have an arc length greater than zero. |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: The curve bounded surface is a parametric surface with curved boundaries defined by one or more boundary curves. The bounded surface is defined to be the portion of the basis surface in the direction of N x T from any point on the boundary, where N is the surface normal and T the boundary curve tangent vector at this point. The region so defined shall be arcwise connected.
Definition from IAI: The IfcCurveBoundedPlane is a specialized bounded surface class that deals only with bounding basis plane surfaces. The definition varies from STEP as outer and inner boundaries are separated attributes and reference the special IFC type Ifc2DCompositeCurve. Only basis surfaces of type IfcPlane are allowed, and the implict_outer attribute has not been incorporated, since only unbounded surfaces are used as basis surface.
NOTE: This is a new class in IFC Release 1.5. The corresponding STEP entity curve_bounded_surface has been changed to meet the specific requirements of an easy representation of curve bounded planes. Only curve bounded planes are allowed in swept area solid, therefore this entity meets the specific requirements of the swept area solid with an easy implementation.
ISSUE: See issue I-225 for changes
made in IFC Release 1.5.
See issue I-333 for changes made
in IFC Release 1.5.1
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
BasisSurface |
The surface to be bound |
n/a |
n/a |
n/a |
|
|
OuterBoundary |
The outer boundary of the surface. |
n/a |
n/a |
n/a |
|
|
InnerBoundaries |
An optional set of inner boundaries. They shall not intersect each other or the outer boundary. |
SET[0:?] Ifc2DCompositeCurve |
0 |
N |
empty |
DER |
Dim |
The space dimensionality of this class, defined by the dimensionality of the basis surface. |
3 |
3 |
3 |
No formal propositions defined at this level.
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: This entity defines a general direction vector in two or three dimensional space. The actual magnitudes of the components have no effect upon the direction being defined, only the ratios X:Y:Z or X:Y are significant.
NOTE: Corresponding STEP entity: direction. The derived attribute Dim has been added at this level and was therefore demoted from the geometric_representation_item. Please refer to ISO/IS 10303-42:1994, p. 26 for the final definition of the formal standard.
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
DirectionRatios |
The components in the direction of X axis (DirectionRatios[1]), of Y axis (DirectionRatios[2]), and of Z axis (DirectionRatios[3]) |
LIST [2:3] REAL |
2 |
3 |
3 |
DER |
Dim |
The space dimensionality of this class, defined by the number of real in the list of DirectionRatios |
2 |
3 |
2 |
Formal Propositions:
WR1 |
The magnitude of the direction vector shall be greater than zero. |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: An IfcElementarySurface is a simple analytic surface with defined parametric representation.
NOTE: Corresponding STEP entity: elementary_surface. Only the subtype plane is incorporated as IfcPlane. The derived attribute Dim has been added at this level and was therefore demoted from the geometric_representation_item. Please refer to ISO/IS 10303-42:1994, p. 69 for the final definition of the formal standard.
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
Position |
The position and orientation of the surface. This attribute is used in the definition of the parameterization of the surface. |
n/a |
n/a |
n/a |
|
DER |
Dim |
The space dimensionality of this class, derived from the dimensionality of the Position |
3 |
3 |
3 |
Formal Propositions:
WR1 |
The magnitude of the direction vector shall be greater than zero. |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: An IfcEllipse is a conic section defined by the lengths of the semi-major and semi-minor diameters and the position (center or mid point of the line joining the foci) and orientation of the curve. Interpretation of the data shall be as follows: C = SELF\IfcConic.Position.Location
x = SELF\IfcConic.Position.P[1]
y = SELF\IfcConic.Position.P[2]
z = SELF\IfcConic.Position.P[3]
R1 = SemiAxis1
R2 = SemiAxis2 and the ellipse is parameterized as:
The parameterization range is 0 £ u £ 2p (or 0 £ u £ 360 degree). In the placement coordinate system defined above, the ellipse is the equation C = 0, where
The positive sense of the ellipse at any point is in the tangent direction, T, to the curve at the point, where
The inherited Position.Location from IfcConic is the center of the IfcEllipse, and the inherited Position.P[1] from IfcConic the direction of the SemiAxis1.
NOTE: Corresponding STEP entity: ellipse. Please refer to ISO/IS 10303-42:1994, p. 39 for the final definition of the formal standard.
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
SemiAxis1 |
The first radius of the ellipse which shall be positive. Placement.Axes[1] gives the direction of the SemiAxis1 |
>0 |
see type |
1 |
|
|
SemiAxis2 |
The second radius of the ellipse which shall be positive. |
>0 |
see type |
1 |
No formal propositions defined at this level.
EXPRESS Definition
Definition from IAI: The IfcExtrudedAreaSolid is defined by sweeping a planar bounded plane. The direction of the extrusion is given by the ExtrudedDirection attribute and the length of the extrusion is given by the Depth attribute. The only allowed area type to be swept is an IfcCurveBoundedPlane, given by the inherited SweptArea attribute from the IfcSweptAreaSolid. If the IfcCurveBoundedPlane has inner boundaries, i.e. holes defined, then those holes shall be swept into holes of the solid.
NOTE: This is a new class in IFC Release 1.5. Corresponding STEP entity: extruded_area_solid. Please refer to ISO/IS 10303-42:1994, p. 183 for the final definition of the formal standard. Note: the data type of the inherited SweptArea attribute is different, i.e. of type IfcCurveBoundedPlane. This complies to WR1 at the supertype swept_area_solid, defining that only planar bounded surfaces are allowed for swept area solids.
ISSUE: See issue I-019 for changes made in IFC Release 1.5.
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
ExtrudedDirection |
The direction in which the surface is to be swept. |
n/a |
n/a |
equal to normal |
|
|
Depth |
The distance the surface is to be swept |
>0 |
see type |
1 |
Formal Propositions:
WR1 |
The ExtrudedDirection shall not be perpendicular to the normal of the plane surface |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: A face is a topological entity of dimensionality 2 corresponding to the intuitive notion of a piece of surface bounded by loops. Its domain, if present, is an oriented, connected, finite 2-manifold in Rm. A face domain shall not have handles but it may have holes, each hole bounded by a loop. The domain of the underlying geometry of the face, if present, does not contain its bounds, and 0 < X < ¥ .
A face is represented by its bounding loops, which are defined as face bounds. A face has a topological normal n and the tangent to a loop is t. For a loop bounding a face with defined geometry, the cross product n x t points toward the interior of the face. That is, each loop runs counter-clockwise around the face when viewed from above, if we consider the normal n to point up. With each loop is associated a BOOLEAN flag to signify whether the loop direction is oriented with respect to the face normal (TRUE) or should be reversed (FALSE).
A face shall have at least one bound, and the loops shall not intersect. One loop is optionally distinguished as the outer loop of the face. If so, it establishes a preferred way of embedding the face domain in the plane, in which the other bounding loops of the face are inside the outer bound. Because the face domain is arcwise connected, no inner loop will contain any other loop. This is true regardless of which embedding in the plane is chosen.
NOTE: Corresponding STEP entity: face. No subtypes of face have been incorporated into this IFC Release. Please refer to ISO/IS 10303-42:1994, p. 140 for the final definition of the formal standard. The WR1 has not been incorporated, since it is always satisfied, due to the fact that only poly loops exist for face bounds.
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
Bounds |
Boundaries of the face. |
SET [1:?] IfcFaceBound |
1 |
N |
1 |
Formal Propositions:
WR2 |
At most one of the bounds shall be of the type IfcFaceOuterBound |
Informal Propositions:
IP1 |
No edge shall be referenced by the face more than twice, |
IP2 |
Distinct face bounds of the face shall have no common vertices. |
IP3 |
If geometry is present, distinct loops of the same face shall not intersect. |
IP4 |
The face shall satisfy the Euler Equation: (number of vertices) - (number of edges) - (number of loops) + (sum of genus for loops) = 0. |
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: A face bound is a loop which is intended to be used for bounding a face.
NOTE: Corresponding STEP entity: face_bound. Please refer to ISO/IS 10303-42:1994, p. 139 for the final definition of the formal standard.
Attributes and Relationships
|
Attribute / Relation |
Definition |
Data or Relation Type |
Min |
Max |
Default |
|
Bound |
The loop which will be used as a face boundary |
n/a |
n/a |
n/a |
|
|
Orientation |
This indicated whether (TRUE) or not (FALSE) the loop has the same sense when used to bound the face as when first defined. If sense is FALSE the senses of all its component oriented edges are implicitly reversed when used in the face. |
BOOLEAN |
see type |
see type |
TRUE |
No formal and informal propositions defined at this level.
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: A face outer bound is a special subtype of face bound which carries the additional semantics of defining an outer boundary on the face. No more than one boundary of a face shall be of this type.
NOTE: Corresponding STEP entity: face_outer_bound. Please refer to ISO/IS 10303-42:1994, p. 139 for the final definition of the formal standard.
No attributes and no formal propositions defined at this level.
EXPRESS Definition
Definition from ISO/CD 10303-42:1992: An IfcFacetedBrep is a simple form of boundary representation model in which all faces are planar and all edges are straight lines. Unlike the B-rep model, edges and vertices are not represented explicitly in the model but are implicitly available through the IfcPolyLoop entity. A faceted B-rep has to meet the same topological constraints as the manifold solid Brep.
NOTE: Corresponding STEP entity: faceted_brep. Please refer to ISO/IS 10303-42:1994, p. 173 for the final definition of the formal standard. Note: In IFC Release 1.5 faceted B-rep with voids is represented by an own subtype and not defined via an implicit ANDOR supertype constraint as in ISO/IS 10303-42:1994. This change has been made due to the fact, that only ONEOF supertype constraint is allowed within the IFC object model.
ISSUE: See issue I-019 for changes made in IFC Release 1.5.
No attributes and no formal propositions defined at this level.
Informal Propositions:
IP1 |
All the bounding loops of all the faces of all the shells in the IfcFacetedBrep shall be of type IfcPolyLoop. |
