IfcBlock是一个构造实体几何（CSG）三维基本体。它由三个正交轴上的位置和正定距离来定义。继承的Position属性具有IfcAxisPlacement3D类型，并提供：
①SELF\IfcCsgPrimitive3D.Position：基本体的轴系统的位置和方向。
②SELF\IfcCsgPrimitive3D。位置。位置：块在位置上有一个顶点，边与放置轴正对齐。
XLength、YLength和ZLength属性定义IfcBlock沿三个轴的大小。
注释定义符合ISO/CD 10303-42:1992
块是实心矩形平行六面体，由位置和放置坐标系定义。块由正长度x、y和z沿放置坐标系的轴指定，并且在放置坐标系的原点处有一个顶点。
注：实体改编自ISO 10303-42中定义的块。
纹理定义
在每个侧面上，纹理都是垂直对齐的。在顶面和底面上，纹理前后对齐。纹理根据重复和重复被拉伸或重复到每个面的范围。
图说明了使用钳制纹理的默认纹理映射（RepeatS=False和repeat=False）。左侧的图像显示了S轴指向右侧而T轴指向上方的纹理。右侧的图像显示应用于几何体的纹理，其中X轴指向右侧，Y轴指向左侧，Z轴指向上方。
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Block textures |
| # | Attribute | Type | Cardinality | Description | C |
|---|---|---|---|---|---|
| IfcRepresentationItem | |||||
| LayerAssignment | IfcPresentationLayerAssignment @AssignedItems |
S[0:1] | Assignment 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. | X | |
| StyledByItem | IfcStyledItem @Item |
S[0:1] | Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve. | X | |
| IfcGeometricRepresentationItem | |||||
| IfcCsgPrimitive3D | |||||
| 1 | Position | IfcAxis2Placement3D | [1:1] | The placement coordinate system to which the parameters of each individual CSG primitive apply. | X |
| Dim :=3 |
IfcDimensionCount | [1:1] | The space dimensionality of this geometric representation item, it is always 3. | X | |
| IfcBlock | |||||
| 2 | XLength | IfcPositiveLengthMeasure | [1:1] | The size of the block along the placement X axis. It is provided by the inherited axis placement through SELF\IfcCsgPrimitive3D.Position.P[1]. | X |
| 3 | YLength | IfcPositiveLengthMeasure | [1:1] | The size of the block along the placement Y axis. It is provided by the inherited axis placement through SELF\IfcCsgPrimitive3D.Position.P[2]. | X |
| 4 | ZLength | IfcPositiveLengthMeasure | [1:1] | The size of the block along the placement Z axis. It is provided by the inherited axis placement through SELF\IfcCsgPrimitive3D.Position.P[3]. | X |
块几何可以用构造性实体几何模型来表示，表示为CSG基元。
EXPRESS Specification
ENTITY IfcBlock
SUBTYPE OF (IfcCsgPrimitive3D);
XLength : IfcPositiveLengthMeasure;
YLength : IfcPositiveLengthMeasure;
ZLength : IfcPositiveLengthMeasure;
END_ENTITY;
原文：https://www.cnblogs.com/herd/p/13186275.html