Hugo Ledoux Geonovum Springplank Amersfoort, the Netherlands 2017-11-27 CityGML is dood, lang leven CityJSON! as an encoding 

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I personally convert immediately to OBJ 3 and I’m not the only one 

CityGML as a data model is ! Its GML encoding is 

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CityJSON v0.5 is already out! 6 

CityJSON v0.5 is already out! 7 All CityGML modules have been mapped 

yeah yeah, I’m fully aware 8 

JSON 9 • JavaScript Object Notation • *not* linked to Java language • Lightweight data-interchange format. • It is easy for humans to read and write. • It is text-based • It is easy for machines to parse and generate. 

Virtually all languages have support for it 10 It is built on two (very common) data structures: 1. collection of name-value pairs • Python dictionaries • hashes • C++ std::map 2. arrays 

I did it by hand… a few observations 11 1. no automatic conversion: that would have yielded the same complexity 2. flattened the schema as much as possible 3. chose City Objects (Buildings, Vegetations, LandUse, etc) and omitted all abstract classes and others 4. chose a geometric model with vertices and references to these (à la OBJ, OFF, etc.) 5. chose to simplify things, eg: • no raster DTM • all primitives in the same CRS • *one* way to represent something 

CityGML Core module, part 1 Copyright © 2012 Open Geospatial Consortium, Inc. All Rights Reserved. 7 +creationDate : xs::date [0..1] +terminationDate : xs::date [0..1] +relativeToTerrain : RelativeToTerrainType [0..1] +relativeToWater : RelativeToWaterType [0..1] <> _CityObject +informationSystem : xs::anyURI [0..1] <> ExternalReference <> CityModel +name : gml::CodeType [0..*] <> gml::_Feature +name : xs::string [1] +uri : xs::anyURI [1] <> ExternalObjectReference <> gml::_FeatureCollection <> Address <> xAL::AddressDetails <> gml::MultiPoint +mimeType : gml::CodeType +transformationMatrix : TransformationMatrix4x4Type +libraryObject : xs::anyURI <> ImplicitGeometry <> gml::_Geometry <> gml::Point +name : xs::string[1] +codeSpace : xs::anyURI[0..1] <> gml::CodeType +entirelyAboveTerrain +substantiallyAboveTerrain +substantiallyAboveAndBelowTerrain +substantiallyBelowTerrain +entirelyBelowTerrain <> RelativeToTerrainType +entirelyAboveWaterSurface +substantiallyAboveWaterSurface +substantiallyAboveAndBelowWaterSurface +substantiallyBelowWaterSurface +entirelyBelowWaterSurface +temporarilyAboveAndBelowWaterSurface <> RelativeToWaterType +gml::doubleList [16] <> TransformationMatrix4x4Type * * cityObjectMember 1 * 0..1 * * 1 externalReference 0..1 * 1 1 externalObject 1 1 * * generalizesTo referencePoint relativeGMLGeometry xalAddress multiPoint Visual Paradigm for UML Standard Edition(Technical University Berlin) 

CityGML geometry model, part 1 Copyright © 2012 Open Geospatial Consortium, Inc. All Rights Reserved. 5 <> gml::_GeometricPrimitive <> gml::_Solid <> gml::_Surface <> gml::_Curve +position : gml::DirectPosition [1] <> gml::Point <> gml::CompositeSolid <> gml::Solid <> gml::CompositeSurface <> gml::TriangulatedSurface <> gml::Triangle +stopLines : gml::LineStringSegment [0..*] +breakLines : gml::LineStringSegment [0..*] +maxLength : gml::LengthType [1] +controlPoint : gml::posList [1] <> gml::TIN <> gml::Polygon +orientation : gml::SignType [0..1] <> gml::OrientableSurface <> gml::CompositeCurve +position : gml::DirectPosition [2..*] <> gml::LineString <> gml::_Ring +position : gml::DirectPosition [4..*] <> gml::LinearRing <> gml::Surface <> gml::_SurfacePatch <> gml::_Geometry <> gml::Rectangle 0..* 0..1 interior * * 1..* * solidMember 1 * * 1 trianglePatches 0..2 1 baseSurface 1 * 1..* * curveMember 1 0..1 exterior 1..* 1 patches 1 * exterior 1..* * surfaceMember interior exterior exterior Visual Paradigm for UML Standard Edition(Technical University Berlin) 

+class : gml::CodeType [0..1] +function : gml::CodeType [0..*] +usage : gml::CodeType [0..*] +yearOfConstruction : xs::gYear [0..1] +yearOfDemolition : xs::gYear [0..1] +roofType : gml:CodeType [0..1] +measuredHeight : gml::LengthType [0..1] +storeysAboveGround : xs::nonNegativeInteger [0..1] +storeysBelowGround : xs::nonNegativeInteger [0..1] +storeyHeightsAboveGround : gml::MeasureOrNullListType [0..1] +storeyHeightsBelowGround : gml::MeasureOrNullListType [0..1] <> _AbstractBuilding <> _BoundarySurface <> CeilingSurface <> InteriorWallSurface <> FloorSurface <> RoofSurface <> WallSurfacee <> ClosureSurface +class : gml::CodeType [0..1] +function : gml::CodeType [0..*] +usage : gml::CodeType [0..*] <> BuildingInstallation +class : gml::CodeType [0..1] +function : gml::CodeType [0..*] +usage : gml::CodeType [0..*] <> IntBuildingInstallation +class : gml::CodeType [0..1] +function : gml::CodeType [0..*] +usage : gml::CodeType [0..*] <> Room +class : gml::CodeType [0..1] +function : gml::CodeType [0..*] +usage : gml::CodeType [0..*] <> BuildingFurniture <> _Opening <> Window <> Door <> Building <> BuildingPart <> core::_CityObject <> gml::MultiCurve <> gml::MultiSurface <> core::_Site <> gml::_Solid <> gml::_Geometry <> core::ImplicitGeometry <> GroundSurface <> OuterCeilingSurface <> OuterFloorSurface <> core::Address * lod4MultiSurface * lod3MultiSurface * * boundedBy * 0..1 * 0..1 * * lod4TerrainIntersection * * lod3MultiSurface * lod2MultiSurface * lod4MultiSurface * lod4MultiCurve * 0..1 interiorFurniture * * address 0..1 * 0..1 * lod3MultiSurface * * interiorRoom 0..1 * lod2MultiSurface * lod4MultiSurface * lod4Geometry * * boundedBy * * outerBuildingInstallation * lod3MultiCurve * 0..1 * lod3ImplicitRepresentation 0..1 * lod4Geometry * * lod4ImplicitRepresentation 0..1 * 0..1 * lod0FootPrint * 0..1 boundedBy 0..1 * lod2MultiCurve * lod0RoofEdge * lod3TerrainIntersection * 0..2 opening 0..1 * lod1MultiSurface * * boundedBy * 0..1 roomInstallation 0..1 * lod4MultiSurface 0..1 * * lod3Geometry * * consistsOfBuildingPart * * interiorBuildingInstallation 0..1 * lod4Geometry * * * address 0..1 * lod1TerrainIntersection 0..1 * lod2Geometry * lod2TerrainIntersection lod4ImplicitRepresentation lod3ImplicitRepresentation lod2ImplicitRepresentation lod4ImplicitRepresentation lod4ImplicitRepresentation lod4Solid lod4Solid lod1Solid lod2Solid lod3Solid 

A CityJSON file 15 { "type": "CityModel", "version": “0.5", "metadata": { "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": [] } } 

A CityJSON file 16 { "type": "CityJSON", "version": “0.5", "metadata": { "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": [] } } version CityJSON 

A CityJSON file 17 { "type": "CityJSON", "version": “0.5", "metadata": { "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": [] } } metadata, ISO19115 “compliant” CityGML has no mechanism, but I felt this is needed ALL geometries have the same CRS, unlike (City)GML 

A CityJSON file 18 { "type": "CityJSON", "version": “0.5", "metadata": { "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": [] } } All City Objects listed here, indexed by their ID Each have geometries + attributes 

A CityJSON file 19 { "type": "CityJSON", "version": “0.5", "metadata": { "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": [] } } Geometry is ID of the vertex, global list compression + more “topology” 

A CityJSON file 20 { "type": "CityJSON", "version": "http://www.cityjson.org/version/0.2", "metadata": { "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": [] } } material + texture possible 

Semantics surfaces, with attributes 21 “geometry": [ { "type": "Solid", “lod": 2.2, "boundaries": [ [ [[0, 3, 2, 1]], [[4, 5, 6, 7]], [[0, 1, 5, 4]], [[1, 2, 6, 5]], [[2, 3, 7, 6]], [[3, 0, 4, 7]] ] ], "semantics": { "surfaces" : [ { "type": "RoofSurface", "slope": 33.4 }, { "type": "RoofSurface", "slope": 66.6 }, { "type": "WallSurface", "paint": "blue" } ], "values": [ [0, 1, null, 2, 2, 2] ] } ] 

BuildingParts: links between City Objects 22 "CityObjects": { "id-1": { "type": "Building", "attributes": { "roofType": "gable" }, "Parts": ["id-56", "id-832"], "Installations": ["mybalcony"] }, "id-56": { "type": "BuildingPart", ... }, "mybalcony": { "type": "BuildingInstallation", ... } } 

BuildingParts: links between City Objects 23 "CityObjects": { "id-1": { "type": "Building", "attributes": { "roofType": "gable" }, "Parts": ["id-56", "id-832"], "Installations": ["mybalcony"] }, "id-56": { "type": "BuildingPart", ... }, "mybalcony": { "type": "BuildingInstallation", ... } } 

Other City Objects 24 "oneparcel": { "type": "LandUse", "geometry": [{ "type": "MultiSurface", "lod": 1, "boundaries": [ [[0, 3, 2, 1]], [[4, 5, 6, 7]], [[0, 1, 5, 4]] ] }] } 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" 

“Is it not like GeoJSON?” 25 1. 3D types not supported (~MultiPatch) 2. Simple Features used (repetitions of coordinates) 3. can’t mix diff types/classes in one file 

I probably borrow more from TopoJSON 26 

JSON Schema: also possible and there’s already one 27 { "$schema": "http://json-schema.org/draft-04/schema#", "title": "CityJSON v0.5", "description": "CityJSON specifications v0.5”, "type": "object", "definitions": { "Building": { "type": "object", "properties": { "type": { "enum": ["Building"] }, "attributes": { "type": "object", "properties": { "creationDate" : {"type": "string"}, "terminationDate" : {"type": "string"}, "class": {"type": "string"}, "function": {"type": "string"}, "usage": {"type": "string"}, … "Solid": { "type": "object", "properties": { "type": { "enum": ["Solid"] }, "boundaries": { "type": "array", "items": { "type": "array", "items": { "type": "array", "items": { "type": "array", "items": {"type": "integer"} 

JSON Schema: also possible and there’s already one 28 { "$schema": "http://json-schema.org/draft-04/schema#", "title": "CityJSON v0.5", "description": "CityJSON specifications v0.5”, "type": "object", "definitions": { "Building": { "type": "object", "properties": { "type": { "enum": ["Building"] }, "attributes": { "type": "object", "properties": { "creationDate" : {"type": "string"}, "terminationDate" : {"type": "string"}, "class": {"type": "string"}, "function": {"type": "string"}, "usage": {"type": "string"}, … "Solid": { "type": "object", "properties": { "type": { "enum": ["Solid"] }, "boundaries": { "type": "array", "items": { "type": "array", "items": { "type": "array", "items": { "type": "array", "items": {"type": "integer"} 

I ate my own dog food 29 

CityJSON will compress ~4X-10X 

often unnecessary repetitions in CityGML 31 … 378548.909850201 5818775.0976939 30.2299995422363 378549.984676693 5818780.48705406 33.23 2014-07-10 378549.012008586 5818780.48695927 30.2299995422363 … … 

often unnecessary repetitions in CityGML 32 … 378548.909850201 5818775.0976939 30.2299995422363 378549.984676693 5818780.48705406 33.23 2014-07-10 378549.012008586 5818780.48695927 30.2299995422363 … … 

often unnecessary repetitions in CityGML 33 … 378548.909850201 5818775.0976939 30.2299995422363 378549.984676693 5818780.48705406 33.23 2014-07-10 378549.012008586 5818780.48695927 30.2299995422363 … … 

often unnecessary repetitions in CityGML 34 … 378548.909850201 5818775.0976939 30.2299995422363 378549.984676693 5818780.48705406 33.23 2014-07-10 378549.012008586 5818780.48695927 30.2299995422363 … … for each of the 19 surfaces of this single building Part of Berlin: • 22,771 buildings • 428,581 semantic surfaces 

Python parser is 1-line 35 import json fin = open('mycity.json') cm = json.loads(fin.read()) print "CRS:", cm['metadata']['crs']['epsg'] print "There are", len(cm['CityObjects']), "CityObjects" # list all ids for id in cm['CityObjects']: print "\t", id 

citygml4j == full conversion from CityGML (beta) 36 #+! to Claus Nagel from virtualcitySYSTEMS 

We need & want your input 

www.cityjson.org (all dev/discussions are open on GitHub) 

thank you. Hugo Ledoux 3d.bk.tudelft.nl/hledoux [email protected]