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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Inference, or from a dense graph to bag of elements
for processing and manipulation
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transactional update
extract valid
subgraphs
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The complete BIM as a set of aspect models
in a federated work environment
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How to export relationships (e.g space boundaries)
when the elements are in disjoint models?
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Application 1 Application 2
?
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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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Boundary Representation (BRep)
u (periodic) ⟶
v ⟶
0 2π
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CGAL Nef Polyhedra
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https://doc.cgal.org/latest/Nef_3/index.html
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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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Relationships in IFC
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Egenhofer spatial predicates
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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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Minkowski sum
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https://www8.cs.umu.se/kurser/TDBAfl/VT06/algorithms/BOOK/BOOK5/NODE199.HTM
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Methodology (e.g wall connectivity)
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wall axis (for qualifying start/end)
wall body
wall boundary volume (computed)
boundary intersection (computed)
legend
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Validation of three public building models
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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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Results spatial containment
two elements contained in wrong storey
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Results wall connectivity
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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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Results wall connectivity (Duplex)
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wrong connection type is supplied | no connectivity information | not touching but for which connection information
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Results space boundaries (Duplex)
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Results space boundaries (Smiley)
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Performance (Duplex)
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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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Conclusion
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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.