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Maybe it’s time to do something with all those ...

Hugo Ledoux
October 13, 2021

Maybe it’s time to do something with all those 3D city models?

Keynote given at 3DGeoInfo 2021 conference (https://3dgeoinfo2021.github.io/) on 2021-10-12

Recording of the talk is also available:
https://youtu.be/EGf3832F1B0

Hugo Ledoux

October 13, 2021
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  1. Hugo Ledoux Delft University of Technology Maybe it’s time to

    do something 
 with all those 3D city models? 3D GeoInfo 2021 at home in my pyjamas 2021-10-12
  2. solar potential shadow analysis noise modelling energy estimation bomb detonation

    wind turbulence pollutant tracking spatial planning • Goal of 3DGeoInfo conferences: push further 3D data modelling • So that 3D datasets are usable and interchangeable • is central as the semantic data model
  3. More and more 3D (open) data from cities 10 Whole

    of the Netherlands: 10M+ LoD1 buildings + terrain, roads, forest, etc. • 3D IMGeo: CityGML ADE • Government could produce the data, but very few could read it • Were the datasets really used?
  4. swisstopo downloads of their 3D model 12 -Raphaël Bovier, from

    his presentation at the 3D city modelling Workshop, Nordic Cooperation in the fi elds of Spatial Data and Land Administration (2021-09-29)
  5. Scientists in other communities are not really involved 13 •

    CFD/simulation community == OBJ/STL • Computer Graphics == OBJ/STL • Other communities have scientists involved in the ecosystem • Why so few here?
  6. UML shouldn’t be the main goal 15 • Many papers

    have as result UML • Most OGC standards focus on the data model • “Let’s model the full reality” → increases complexity • We stay at the theoretical level • Users are not central
  7. Quiz: you need to store 2D polygons, which one you

    choose? 17 GML 3.2.2 specs (427 pages) GeoJSON specs (28 pages )
  8. ADEs: where are the schemas? 18 Biljecki F, Kumar K,

    and Nagel C (2018). CityGML Application Domain Extension (ADE): overview of developments. Open Geospatial Data, Software and Standards (2018) 3:13 • Only 18/44 ADEs have XSD schemas available • Some don’t have UML, just a description Files with ADEs are way more difficult to read than “vanilla” ones ➡ custom code
  9. Little focus on usable datasets 19 • Assumed encoding (GML)

    can be automatically derived from schemas • Datasets are often hierarchical and have annoying quirks
  10. Real-life reactions of students in my course 22 When learning

    about semantic 3D city models Trying to read a CityGML file with Python
  11. Many of us promote semantic formats but use… OBJ/STL 23

    • OBJ and STL are super simple • They are used for decades in computer graphics, CFD, etc • Many software support them They. Just. Work.
  12. OK, but concretely here? 26 1. Make one usable profile

    of CityGML that supports most important parts (similar to Simple Features) 2. Please no GML for the encoding, no developers want this 3. Write parsers for the format (Python, JS, C++) so that others can just reuse/copy. Maybe an API to manipulate the data? 4. Think “like a designer” (how will the product be used?) 5. “Eat your own dog food”
  13. CityJSON v1.0 28 1. "Building" 2. "BuildingPart" 3. "BuildingInstallation" 4.

    "Road" 5. "Railway" 6. "TransportSquare" 7. "TINRelief" 8. "WaterBody" 9. "PlantCover" 10. "SolitaryVegetationObject" 11. "LandUse" 12. "CityFurniture" 13. "GenericCityObject" 14. "Bridge" 15. "BridgePart" 16. "BridgeInstallation" 17. "BridgeConstructionElement" 18. "Tunnel" 19. "TunnelPart" 20. “TunnelInstallation” 21. “CityObjectGroup” • community standard • all modules of CityGML v2.0 are mapped 💪 • Subset of CityGML (~97% of features) • software for full conversion CityGML <-> CityJSON • several software support it
  14. Same information as CityGML, but in JSON format 29 {

    "type": “CityJSON", "version": “1.0”, "metadata": { "referenceSystem": "urn:ogc:def:crs:EPSG::7415", }, "CityObjects": { "id-1": { "type": "Building", "attributes": { "measuredHeight": 22.3, "roofType": "gable", "owner": “Elvis Presley" }, "geometry": [ { "type": "MultiSurface", "boundaries": [ [[0, 3, 2, 1]], [[4, 5, 6, 7]], [[0, 1, 5, 4]] ] } ] } }, "vertices": [ [23.1, 2321.2, 11.0], [111.1, 321.1, 12.0], ... ], "appearance": { "materials": [], "textures":[], "vertices-texture": [] } } human-readable file computers prefer this over XML ~6X compacter than CityGML
  15. LoD 2.2 
 reconstruction 3D BAG is based on open

    datasets 34 Point cloud (AHN3) Footprint (BAG) + X 10,000,000 100% automatic
  16. 3D BAG is tiled into *small* and *manageable* datasets 36

    BAG polygons Quadtree Max 3500 buildings per tile
  17. Download is simple and fast 37 Stats last 2 weeks

    (~32000 downloads) CityJSON 56% OBJ 23% GPKG 21% PostgreSQL <1%