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

Transcript

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 3 New York City (LoD2)
4. More and more 3D (open) data from cities 4 Switzerland: 70M 3D objects are now open
5. More and more 3D (open) data from cities 5 Helsinki: LoD2 with textures
6. More and more 3D (open) data from cities 6 56 cities in Japan
7. More and more 3D (open) data from cities/countries 7 41 cities/countries!
8. So, mission accomplished!? 8
9. Yeah, not so sure…
10. 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?
11. Where is the File/Open CityGML? 11
12. 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)
13. 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?
14. Why are the datasets seldom used?
15. 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
16. Standards don’t ensure usefulness (quite the contrary one might say…) 16
17. Quiz: you need to store 2D polygons, which one you choose? 17 GML 3.2.2 specs (427 pages) GeoJSON specs (28 pages )
18. 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
19. Little focus on usable datasets 19 • Assumed encoding (GML) can be automatically derived from schemas • Datasets are often hierarchical and have annoying quirks
20. “GML madness”: how many ways to store a simple square? 20 25 different ways
21. Complex formats usually have fewer software support 21 No known JavaScript parser for CityGML files!?
22. Real-life reactions of students in my course 22 When learning about semantic 3D city models Trying to read a CityGML file with Python
23. 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.
24. What can we do about it?
25. Shouldn’t we apply the Rule of Least Power? 25
26. 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”
27. Two projects where we applied those principles
28. 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
29. 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
30. Python parsing is very easy 30
31. CityJSON can be easily parsed with JavaScript 31 Developed by MSc students
32. CityJSON is “ready” for machine learning 32 new!
33. 3D BAG: all 10M+ buildings in the Netherlands 33 https://3dbag.nl
34. LoD 2.2 
 reconstruction 3D BAG is based on open datasets 34 Point cloud (AHN3) Footprint (BAG) + X 10,000,000 100% automatic
35. 3 different LoDs 35
36. 3D BAG is tiled into *small* and *manageable* datasets 36 BAG polygons Quadtree Max 3500 buildings per tile
37. Download is simple and fast 37 Stats last 2 weeks (~32000 downloads) CityJSON 56% OBJ 23% GPKG 21% PostgreSQL <1%
38. Very careful about geometric validity 38 ~98% valid
39. Amsterdam put our data in their Unity online platform within days 39
40. People outside our field used the data 40 Historical cadastre Shadow analysis
41. We reached non-geo people 41
42. thank you. h.ledoux@tudelft.nl 3d.bk.tudelft.nl/hledoux Hugo Ledoux https://cityjson.org https://3dbag.nl