2020 Volume 45 Issue 275 Pages 17-23
The IFC specification developed by buildingSMART has been accepted as an ISO standard for building information modeling since March 2013. IFC data have been used directly in many projects. It is important to get the information about geometric shape and local placement of walls in heating and cooling load calculation and CFD simulation. In this article, according to the specification of IFC2x3, the tree structure of the IFC classes is illustrated, especially the information related to the geometric shape and local placement of the IfcProduct class. First, the IFC data of a sloped wall are exported by ArchiCAD. Then, the shape representation and local placement attributes of the IfcWall are exemplified. Next, the coordinates of vertexes of the sloped wall are calculated using the coordinate transformation matrix defined by the position attribute of the IfcAxis2Placement3D class, according to the attributions of SweptArea, ExtrudedDirection, and Depth of the IfcExtrudedAreaSolid. The local placement of the wall is calculated using the coordinate transformation matrices defined by the coordinate systems of the related building story and building, as well as the extruded direction. Finally, the calculated coordinates of vertexes of the sloped wall are confirmed with those modeled in the BIM software. Furthermore, care should be taken to ensure the precision of real numbers during the calculation. The IfcExtrudedAreaSolid is a typical shape-representation class in the IFC specification. And the proposed coordinate transformation method is available for the other shape-representation IFC entities, which will be helpful for the use of IFC data of building elements in heating and cooling load calculation and CFD simulation.
