IFC 4.3.x development IfcBlock Semantic definitions at the entity

The IfcBlock is a Construction Solid Geometry (CSG) 3D primitive. It is defined by a position and a positve distance along the three orthogonal axes. The inherited Position attribute has the IfcAxisPlacement3D type and provides:

  • SELF\IfcCsgPrimitive3D.Position: The location and orientation of the axis system for the primitive.
  • SELF\IfcCsgPrimitive3D.Position.Location: The block has one vertex at location and the edges are aligned with the placement axes in the positive sense.

The XLength, YLength, and ZLength attributes define the size of the IfcBlock along the three axes.


Figure 1 illustrates geometric parameters of a block where the block positioned within its own placement coordinate system. The values for XLength, YLength, and ZLength are applied to the positive direction of the X, Y, and Z axis.

Figure 1 — Block geometry


NOTE  Definition according to ISO/CD 10303-42:1992
A block is a solid rectangular parallelepiped, defined with a location and placement coordinate system. The block is specified by the positive lengths x, y, and z along the axes of the placement coordinate system, and has one vertex at the origin of the placement coordinate system.

NOTE  Entity adapted from block defined in ISO 10303-42.

HISTORY  New entity in IFC2x3.

Texture definition

On each side face, textures are aligned facing upright. On the top and bottom faces, textures are aligned facing front-to-back. Textures are stretched or repeated to the extent of each face according to RepeatS and RepeatT.

Figure 2 illustrates default texture mapping with a clamped texture (RepeatS=False and RepeatT=False). The image on the left shows the texture where the S axis points to the right and the T axis points up. The image on the right shows the texture applied to the geometry where the X axis points back to the right, the Y axis points back to the left, and the Z axis points up.


Side Normal Origin X Origin Y Origin Z S Axis T Axis
Left -X 0 +YLength 0 -Y +Z
Right +X +XLength 0 0 +Y +Z
Front -Y 0 0 0 +X +Z
Back +Y +XLength +YLength 0 -X +Z
Bottom -Z 0 +YLength 0 +X -Y
Top +Z 0 0 +ZLength +X +Y

Figure 2 — Block textures Attributes

# Attribute Type Description
LayerAssignmentSET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItemsAssignment of the representation item to a single or multiple layer(s). The LayerAssignments can override a LayerAssignments of the IfcRepresentation it is used within the list of Items.

> IFC2x3 CHANGE  The inverse attribute LayerAssignments has been added.

> IFC4 CHANGE  The inverse attribute LayerAssignment has been restricted to max 1. Upward compatibility for file based exchange is guaranteed.
StyledByItem SET [0:1] OF IfcStyledItem FOR Item Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve.

> IFC2x3 CHANGE  The inverse attribute StyledByItem has been added.
1 Position IfcAxis2Placement3D The placement coordinate system to which the parameters of each individual CSG primitive apply.
Dim INVALID The space dimensionality of this geometric representation item, it is always 3.
2 XLength IfcPositiveLengthMeasure The size of the block along the placement X axis. It is provided by the inherited axis placement through _SELF\IfcCsgPrimitive3D.Position.P[1]_.
3 YLength IfcPositiveLengthMeasure The size of the block along the placement Y axis. It is provided by the inherited axis placement through _SELF\IfcCsgPrimitive3D.Position.P[2]_.
4 ZLength IfcPositiveLengthMeasure The size of the block along the placement Z axis. It is provided by the inherited axis placement through _SELF\IfcCsgPrimitive3D.Position.P[3]_. Entity inheritance

dot_inheritance IfcBlock IfcBlock IfcCsgPrimitive3D IfcCsgPrimitive3D IfcBlock->IfcCsgPrimitive3D IfcCsgPrimitive3D_children 4 more... IfcCsgPrimitive3D_children->IfcCsgPrimitive3D IfcGeometricRepresentationItem IfcGeometricRepresentationItem IfcCsgPrimitive3D->IfcGeometricRepresentationItem IfcGeometricRepresentationItem_children 24 more... IfcGeometricRepresentationItem_children->IfcGeometricRepresentationItem IfcRepresentationItem IfcRepresentationItem IfcGeometricRepresentationItem->IfcRepresentationItem IfcRepresentationItem_children 3 more... IfcRepresentationItem_children->IfcRepresentationItem Formal representations

 SUBTYPE OF (IfcCsgPrimitive3D);
	XLength : IfcPositiveLengthMeasure;
	YLength : IfcPositiveLengthMeasure;
	ZLength : IfcPositiveLengthMeasure;