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(CityJSON == CityGML) && (CityGML == CityJSON) Geonovum sessie over 3D Amersfoort 2023-10-03 Hugo Ledoux TUDelft

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(CityJSON == CityGML) && (CityGML == CityJSON) Geonovum sessie over 3D Amersfoort 2023-10-03 Hugo Ledoux TUDelft Full disclosure: I started CityJSON and I’m still an editor

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2 International standard (from OGC) for representing and storing semantic 3D city models v1.0 in 2008 v2.0 in 2012 v3.0 in 2021 & 2023

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3 Data model XML/GML encoding 4 encodings 3D City DB cjdb

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4 Data model == UML Encoding == XML or JSON or … { "type": “CityJSON", "version": “2.0”, "transform": { "scale": [1.0, 1.0, 1.0], "translate": [0.0, 0.0, 0.0] }, "metadata": { "referenceSystem": "https://www.opengis.net/def/crs/EPSG/0/7415" }, "CityObjects": { "id-1": { "type": "Building", "attributes": { "measuredHeight": 22.3, "owner": “Elvis Presley" }, "geometry": [ { "type": “MultiSurface", "lod": “2.1", "boundaries": [ [[0, 3, 2, 1]], [[4, 5, 6, 7]], [[0, 1, 5, 4]] ] } ] } }, "vertices": [ [231, 2321, 11], [1111, 321, 12], ... ], "appearance": { "materials": [], "textures":[] } }

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CityGML v3.0 5 • Adds interior of buildings (rooms, storeys, etc) • no more LoD4 • Adds point clouds, versioning, etc. • Revamp of the ADE mechanism Data model released in 2021

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CityGML-XML v3.0 6 XML encoding released in June 2023 • No software support at the moment: FME will **not** work • Except citygml4j (from the main CityGML developer)

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CityGML files are very complex 7 • files are deeply nested, and large • many “points of entry” • many di ff ways to do one thing ➡ few software packages correctly read/write CityGML-XML ➡ no parsers in JavaScript ➡ I personally get 😩 each time I get a new file it makes the life of developers very unpleasant

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CityGML files are very complex 7 • files are deeply nested, and large • many “points of entry” • many di ff ways to do one thing ➡ few software packages correctly read/write CityGML-XML ➡ no parsers in JavaScript ➡ I personally get 😩 each time I get a new file it makes the life of developers very unpleasant

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v2.0 just released! Approved by CityGML v3.0 conformant

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CityJSON v2.0 implements most of CityGML data model 9 • all core modules of CityGML data model v3.0 are mapped 💪 • Subset of CityGML core (~97% of features) • Modules not supported is on purpose (to keep it simple)

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GIS specialists do not all use/have FME: Python parsing is very easy 10 CityJSON makes developers happy (and thus productive)

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It’s ready for the web 11

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It’s ready for the web 11

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Compression of files: Zürich LoD2 buildings 12 CityGML-XML v2.0 = 3.0GB (but 1GB of spaces/CRs/tabs!) CityJSON v2.0 = 292MB Compression == 7.1X

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Compression of files: Zürich LoD2 buildings 12 CityGML-XML v2.0 = 3.0GB (but 1GB of spaces/CRs/tabs!) CityJSON v2.0 = 292MB Compression == 7.1X

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CityJSON support in software 13 Good list of software Most are open-source Many written by students at TUDelft

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(CityJSON == CityGML) && (CityGML == CityJSON)

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citygml4j + citygml-tools 15 full conversion CityGML <-> CityJSON • Supports CityGML-XML v3.0 • Bidirectional conversion • Open-source

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CityJSON 🔄 CityGML 16

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CityJSON 🔄 CityGML 16

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Certainly it can’t be that simple? Indeed, there are 2 caveats 17 #1. ADEs != Extensions #2. CityGML modules not supported in CityJSON

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thank you. h.ledoux@tudelft.nl 3d.bk.tudelft.nl/hledoux Hugo Ledoux https://cityjson.org https://citygml.org 3DBAG has all 10M buildings in NL in CityJSON