Conversion of IFC to CityGML

Transcription

1 Technische Universität Berlin Conversion of IFC to CityGML Claus Nagel Thomas H. Kolbe Institute for Geodesy and Geoinformation Science Technische Universität Berlin OGC 3DIM WG, Paris

2 Agenda Part I: Talk about Master s thesis Research task: Development of an algorithm allowing for the fully automated transformation of IFC building models into a geometrically and semantically valid representation for the Level-of-Detail (LOD) of CityGML Research Center Karlsruhe, Institute for Applied Computer Science Hochschule Karlsruhe, University of Applied Sciences Part II: Live demonstration of the software application IfcExplorer developed at the Research Center Karlsruhe 2 Claus Nagel

3 IFC building model (informal UML diagram) IfcProject 0.. IfcSite 0.. IfcObject IfcProduct <<Relation>> IfcPropertyXXX <<Geometry>> IfcShapeRepresentation <<Geometry>> IfcLocalPlacement IfcWall IfcCurtainWall IfcBeam IfcWindow IfcSlab IfcRamp 0.. IfcBuilding 0.. IfcBuildingStorey IfcSpatialStructureElement IfcElement IfcFlowTerminal IfcDoor IfcColumn IfcCovering IfcRampFlight IfcStairFlight IfcRailing 0.. IfcSpace IfcOpeningElement 0.. IfcBuildingElement IfcStair IfcRoof based on ISO Claus Nagel

4 CityGML building model (excerpt) _CityObject <<Geometry>> gml::_solid _Site <<Geometry>> gml::multisurface <<Geometry>> gml:: MultiCurve lodx, lodx, X [..4] lodx, X [..4] X [2..4] Room _AbstractBuilding lod4 lodx, X [2..4] 0.. lodx, X [3..4] CeilingSurface InteriorWallSurface FloorSurface RoofSurface BuildingFurniture IntBuildingInstallation lod4 lod <<Geometry>> gml::_geometry BuildingInstallation lodx, 0.. X [2..4] _BoundarySurface 0..2 WallSurface GroundSurface ClosureSurface Door Window _Opening based on ISO 907 and ISO Claus Nagel

5 Comparison of IFC and CityGML 5 Claus Nagel

6 Model transformation Element-based volume model IFC Model transformation semantic level geometric level Surface model CityGML 6 Claus Nagel

7 Model transformation Objective: Derivation of a valid representation for the LOD of CityGML Characteristics of LOD: Blocks model Prismatic buildings Approximated exterior shell Flat roofs No roof overhangs No slab overhangs 7 Claus Nagel

8 Model transformation Step : Simplification on the semantic model level Focusing on building elements forming the exterior shell. Horizontal building elements e.g. IfcSlab 2. Vertical building elements e.g. IfcWall, IfcColumn, IfcBeam 3. Roof elements Result: Simplified view of the IFC building model 8 Claus Nagel

9 Model transformation Step 2: Two-dimensional approach Projection of the 3D silhouette of each horizontal and vertical building element onto the x-y plane Each building storey is considered separately Allows for the identification of shape changes of the exterior shell Result: Element-based contour polygons 9 Claus Nagel

10 Model transformation Step 3: Determination of storey footprints Union of the element-based contour polygons using 2D Boolean operations Element-based view of the IFC is resolved Result: Separate footprints for each building storey 0 Claus Nagel

11 Model transformation Step 4: Linear extrusion of storey footprints Transformation of the 2D storey footprints into 3D extruded solids Extrusion profile is defined by the storey footprint Extrusion axis is pointing into the direction of the z-axis Extrusion height is determined by the extension of the building storey Result: Boundary surfaces for each building storey Claus Nagel

12 Model transformation Step 5: Generalization of roof elements Transformation into 3D extruded solids according to the steps applied to the building storeys Extrusion height is generally equivalent to the ridge height Roof structures such as dormers are generalized Trimming of roof overhangs using 2D Boolean operations 2 Claus Nagel

13 Model transformation Step 6: Composition of the resulting surface model Merging of adjacent extruded solids with the same footprint Identification of the boundary surfaces Result: Final LOD surface model 3 Claus Nagel

14 Subsets of the transformation steps 4 Claus Nagel

15 Subsets of the transformation steps 2 5 Claus Nagel

16 Subsets of the transformation steps Claus Nagel

17 Example Transformation of a city scene composed of 95 separate IFC building models Building models Data volume 28.0 MB.24 MB Computation time [sec] Solids Claus Nagel

18 Conclusions Need for transformation of IFC building models into semantically and geometrically valid representations for CityGML Development of a transformation algorithm Derivation of LOD building models Formal mapping rules allowing for a fully automated model transformation Realized in the software application IFCExplorer of the Research Center Karlsruhe Outlook Derivation of LOD2 building models based on the presented transformation steps is also possible Generalization of roof elements using prototypical roof models Semantic differentiation of the boundary surfaces 8 Claus Nagel

19 Contact details Technical University of Berlin Institute for Geodesy and Geoinformation Science Claus Nagel, Thomas H. Kolbe {nagel Web: Research Center Karlsruhe Institute for Applied Computer Science Karl-Heinz Haefele Web: 9 Claus Nagel

20 Technische Universität Berlin Thank you Claus Nagel Thomas H. Kolbe {nagel OGC 3DIM WG, Paris