Storage, Maintenance and Dissemination of Massive 3D City Objects

by 3D4EM

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Storage, Maintenance and Dissemination of Massive 3D City Objects Kavisha 31-05-2016 3D4EM Meeting

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Terrain as TIN

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Terrain as Raster

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Terrain as TIN + Grid

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What we have??

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Challenges with current solution: CityGML

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Voluminous data • CityGML 3DTOPNL Terrains : TIN : ~700 GB (1 billion triangles) ( x 1 , y 1 , z 1) ( x 2 , y 2 , z 2) ( x 3 , y 3 , z 3) < gml : triangle > < gml : exterior > < gml : LinearRing > < gml : posList > x 1 y 1 z 1 x 2 y 2 z 2 x 3 y 3 z 3 x 1 y 1 z 1 < /gml : posList > < gml : LinearRing > < gml : exterior > < gml : triangle > OGC Simple Feature No referencing No TIN topology

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No distinct LODs

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Problems • No support for terrain topology in: • CityGML TINRelief and • CityGML MassPointRelief

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Nothing for Tiling Unsafe Triangles Tile 1 Tile 2 Tile 3 Tile 4 Tile Boundary Triangles spanning multiple tiles

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Skeptical TIN !! Why separate class??

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Grids : vague!! • Raster/Grid terrains in CityGML. GML schema Vague?? No sample data!!

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Terrain as TIN + Grid TIN Relief Grid Coverage validity polygon Not at the centre of grid cell

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Not suitable for 3D Viz

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Framework

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What needs to be done? • Redeﬁnition of conceptual model of geometry in the CityGML schema for terrains.

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What needs to be done? P1 P2 P3 …

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Terrains@CityGML

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Terrain@CityGML • CityGML 3DTOPNL Terrains : ~700 GB (1 billion triangles) • For 1 tile: • CityGML: ~ 740 MB • Terrains@CityGML: ~ 30 MB ~25x less storage space Compressed workable ﬁle (~5 to 7 MBs for 1 tile)

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CityGML vs Terrain@CityGML

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Really Triangles??: YES

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Terrains@CityGML with Cesium

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3D over Cesium • A s g e o m e t r y ( P o l y g o n / B o x / C y l i n d e r / Rectangle,..etc.)

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3D over Cesium • A s g e o m e t r y ( P o l y g o n / B o x / C y l i n d e r / Rectangle,..etc.) Coordinates

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3D over Cesium • A s g l T F ( G L Tr a n s m i s s i o n F o r m a t ) : Interoperability??

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A way around glTF Terrains@CityGML Parser JSON Description ﬁle Binary data ﬁle Textures Cesium API 30 MB 8 KB 24 MB

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As Quantized Mesh • At present: • only height maps for Rasters • No TIN implementation Terrains@CityGML Generate Quadtree Cesium API Generate header .terrain tiles Cesium Terrain Server

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Terrains @Cesium • As Quantized mesh • indexed triangles as quad pyramids of height maps