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Validation and Inference of Geometrical Relationships in IFC

Validation and Inference of Geometrical Relationships in IFC

Presentation of the paper available at http://dx.doi.org/10.46421/2706-6568.37.2020.paper008

Abstract: The Industry Foundation Classes are a prevalent open standard to exchange Building Information Models. In such a model, geometric representations are provided for individual building elements along with semantic information, including a significant amount of properties related to geometry and explicit topological relationships. These relationships and quantities introduce redundancies and often inconsistencies as well. Moreover, they introduce complexity in down-stream processing. Combining multiple aspect models into a single model has non-trivial consequences for the connectivity graphs. Programmatic mutations are complicated because of the relationships that need to be updated as a result of changes.
In order to alleviate these issues, this paper provides a theoretical framework and implementation for both validating and inferring semantic and topological con-structs from the geometric representations, rooted on Egenhofer spatial predicates and extended with the IFC modelling tolerance. Combining these two concepts, wall connectivity is equivalent to the intersection of the wall representation boundaries, where a boundary is not a surface, but rather a hollow solid with a thickness derived from the modelling tolerance.
The algorithms presented in this paper are implemented in fully open source software based on the IfcOpenShell software library and the CGAL computational geometry library using Nef polyhedra. We provide a formalization of space boundaries, spatial containment and wall connectivity relationships. The validation and inference rules are applied to a public set of building models. We conclude that exported models have geometric flaws and that several relationships can indeed be inferred by means of generic geometric intersection logic.


Thomas Krijnen

August 19, 2020



    3B.5 Thomas Krijnen, Delft University of Technology, NL Francesca Noardo, Ken Arroyo Ohori, Hugo Ledoux, and Jantien Stoter
  2. 18-20 August Inference, or from a dense graph to bag

    of elements for processing and manipulation 2 transactional update extract valid subgraphs
  3. 18-20 August The complete BIM as a set of aspect

    models in a federated work environment 3
  4. 18-20 August How to export relationships (e.g space boundaries) when

    the elements are in disjoint models? 4 Application 1 Application 2 ?
  5. 18-20 August 5 Implementation https://github.com/tudelft3d/IfcOpenShell/blob/cgal/src/ifcconvert/validate_wall_connectivity.cpp IfcOpenShell the open source ifc

    toolkit and geometry engine
  6. 18-20 August 6 Boundary Representation (BRep) u (periodic) ⟶ v

    ⟶ 0 2π
  7. 18-20 August CGAL Nef Polyhedra 7 https://doc.cgal.org/latest/Nef_3/index.html

  8. 18-20 August 8 Boundary Representation matches IFC geometry model curved

    surfaces and semantics (like radii) CGAL Nef Polyhedra arbitrarily precise number types lazy exact evaluation: propagating rounding errors to interval | fallback to exact when uncertain closed under all binary set operations
  9. 18-20 August Relationships in IFC 9

  10. 18-20 August Egenhofer spatial predicates 10 EGENHOFER & FRANZOSA (1991)

    Point-set topological spatial relations, International Journal of Geographical Information System, 5:2, 161-174, DOI: 10.1080/02693799108927841
  11. 18-20 August Minkowski sum 11 https://www8.cs.umu.se/kurser/TDBAfl/VT06/algorithms/BOOK/BOOK5/NODE199.HTM

  12. 18-20 August Methodology (e.g wall connectivity) 12 wall axis (for

    qualifying start/end) wall body wall boundary volume (computed) boundary intersection (computed) legend
  13. 18-20 August Validation of three public building models 13 Duplex1,

    Fzk2, and Smiley3; 1 IFC2X3; Autodesk Revit Architecture 2011; U.S Army, Corps of Engineers 2 IFC2X_FINAL; Autodesk Architectural Desktop; Automation and Applied Informatics (IAI) / Karlsruhe Institute of Technology (KIT) 3 IFC4; Archicad 20; IAI / KIT
  14. 18-20 August Results spatial containment two elements contained in wrong

    storey 14
  15. 18-20 August Results wall connectivity 15 Duplex Fzk Smiley missing

    relation 2 2 0 invalid relation: wrong connection type 4 6 0 invalid relation: walls not touching 8 0 0
  16. 18-20 August Results wall connectivity (Duplex) 16 wrong connection type

    is supplied | no connectivity information | not touching but for which connection information
  17. 18-20 August Results space boundaries (Duplex) 17

  18. 18-20 August Results space boundaries (Smiley) 18

  19. 18-20 August Performance (Duplex) 19 Task Time (s) a. IFC

    parsing (tokenization and storage) 0.7174 b. Geometry mapping 0.0364 c. Geometry creation 0.5732 d. Conversion to Nef polyhedron 1.4116 e. Minkowski sum with small cube 7.0064 f. 3D Box intersection pairs 0.0006 g. Boolean intersection on Nef 16.5032 h. Conversion of result back to polyhedron 1.5342
  20. 18-20 August Conclusion 20 Infered connections to enable distributed and

    transactional working Geometrical validation shows all assessed models contain flaws Calculate predicates and quantities to comply to local norms Exact CGAL Nef Polyhedra are robust, but the Minkowski sum is slow on concave inputs.