IFC Data Transfer

The data transfer is based on the IFC version IFC 2x3.

Coordinate System

In the IFC product model the z axis of the global coordinate system typically runs from below to above. This is counter to the convention used in InfoCAD. To avoid all objects standing on their heads after an export or import, they are turned 180° around the global x axis. If this proves to be problematic during practical use, it is possible to depart from the normal convention and change the direction of the z axis using a suitable program extension.

Import

The data import consists of two functional areas:

• Importing Frameworks
• Importing the Geometry of Building Elements

1. Importing Frameworks

The import of frameworks is carried out for the static calculation models (IfcStructuralAnalysisModel) saved in the transfer file and selected by the user. The following table displays the relevant objects.

Example

The following illustrations display the import of a framework from file ’gtstrudl_physical.ifc’. Source: http://cic.nist.gov/vrml/cis2.html (NIST, National Institute of Standards and Technology)

Dialog for selecting the import data	Imported framework

The file contains a analysis model with the name ’Loads and Results Exported from GTSTRUDL’ and also building elements of various types that have been deselected for import. To import frameworks, either the FEM or the RSW static mode must be active.

2. Importing the Geometry of the Building Elements

This functional area calls for construction model objects saved in the transfer file whose type is derived from IfcBuildingElement. They include, for example, IfcBeam, IfcColumn, IfcSlab and IfcWall(StandardCase). Only objects with the geometric display ‘SweptSolid,' 'Clipping,' 'Brep,' and 'MappedRepresentation' are considered. In InfoCAD special drawing objects are generated from these that make it possible to continue to use the geometry of the building elements. The snap modes ’End’, ’Middle’, and ’Normal’ allow you to use, for instance, characteristic points for measurements or for the design of model objects.

Example

Building elements from the ’gtstrudl_physical.ifc’ file. Source: http://cic.nist.gov/vrml/cis2.html
(NIST, National Institute of Standards and Technology)

The figure above shows several further characteristics that are imported in addition to the geometry of the building elements. These include

• GlobalId: identification of the building element
• Name, Descrip.: description
• Material: assossiated material description
• LoadBe(aring): displays whether the element bears load (1) or not (0)

Transformation into Model Objects

Imported drawing objects whose geometric display is based on the extrusion of a base area (IfcExtrudedAreaSolid) and who originate from

• IfcBeam
• IfcColumn
• IfcMember
• IfcSlab
• IfcWall(StandardCase)

can be transformed, with the help of the program, into model objects (select ’Transform’ from the shortcut menu, FEM static mode). As part of this process, linear elements are turned into edges with the meaning ’Free beam’. The generated beam section corresponds to the profile definition used for the base area. Objects originating from IfcSlab and IfcWall whose base area consists of a traverse with exactly four points are converted into model surfaces.

The following illustration displays some of the building elements from the file ’AC-90Smiley-West-14-07-2005.ifc’, as well as the resulting model surfaces.
Source: http://www.iai.fzk.de.

Geometry of the building elements

Model objects, not joined

Because the model objects are created based on the wall or plate axis surfaces, gaps usually exists between neighboring objects (see detail). As a remedy, all objects are joined with one another during the transformation and, if necessary, marginally reduced or enlarged. If for walls standing on top of each other the wall axes do not match up, for instance due to differing wall thickness, it might be necessary to add transition surfaces that are not perpendicular. In addition, openings that are close to the edge are adjusted.

The described operations help to improve the continuity between the model objects. This can eliminate the need for manual corrections in many cases. The following illustrations show the joined model objects and the element mesh that has been created as a result.

Model objects, joined

Generated element mesh

Export

The export function currently only applies to the data from 3D frameworks:

• Static calculation model without results
• Construction model with the objects IfcBeam, IfcColumn

Framework exported with InfoCAD displayed in IfcStoreyView (Forschungszentrum Karlsruhe, Institut für angewandte Informatik)

InfoCAD_IFC