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.

Transcript

1. 18-20 August
   VALIDATION AND INFERENCE OF GEOMETRICAL
   RELATIONSHIPS IN IFC
   3B.5
   Thomas Krijnen, Delft University of Technology, NL
   Francesca Noardo, Ken Arroyo Ohori, Hugo Ledoux, and Jantien Stoter
   

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2. 18-20 August
   Inference, or from a dense graph to bag of elements
   for processing and manipulation
   2
   transactional update
   extract valid
   subgraphs
   

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3. 18-20 August
   The complete BIM as a set of aspect models
   in a federated work environment
   3
   

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4. 18-20 August
   How to export relationships (e.g space boundaries)
   when the elements are in disjoint models?
   4
   Application 1 Application 2
   ?
   

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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
   

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6. 18-20 August
   6
   Boundary Representation (BRep)
   u (periodic) ⟶
   v ⟶
   0 2π
   

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

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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
   

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9. 18-20 August
   Relationships in IFC
   9
   

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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
    

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11. 18-20 August
    Minkowski sum
    11
    https://www8.cs.umu.se/kurser/TDBAfl/VT06/algorithms/BOOK/BOOK5/NODE199.HTM
    

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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
    

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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
    

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14. 18-20 August
    Results spatial containment
    two elements contained in wrong storey
    14
    

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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
    

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16. 18-20 August
    Results wall connectivity (Duplex)
    16
    wrong connection type is supplied | no connectivity information | not touching but for which connection information
    

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17. 18-20 August
    Results space boundaries (Duplex)
    17
    

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

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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
    

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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.
    

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