How useful are current 3D city models?
Hugo Ledoux
102nd OGC Technical Committee
TU Delft, the Netherlands
2017-03-20
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Not only my work, but that of my research group
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Not only my work, but that of my research group
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•Mathematically easy but tools are needed
From multiple representation to
higher dimensional GIS
x
y
z
time scale
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More and more 3D (open) data from cities
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Whole North
Rhine-Westphalia:
10M+ LoD2
buildings
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More and more 3D (open) data from cities
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New York City
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More and more 3D (open) data from cities
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Helsinki: with
textures
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More and more 3D (open) data from cities
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Whole of the
Netherlands:
10M+ LoD1 buildings +
terrain, roads, forest
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More and more 3D (open) data from cities
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Why do cities reconstruct
their 3D city model?
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solar potential
shadow analysis
noise modelling
energy estimation
bomb detonation
wind turbulence
pollutant tracking
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3D in the mainstream: NY Times shadow analysis
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https://www.nytimes.com/interactive/2016/12/21/upshot/Mapping-the-Shadows-of-New-York-City.html
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Environmental law: from 2018 in NL
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Video “Stip op de horizon: Dynamisch 3D model” from Municipality of The Hague
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How are geometric errors
affecting applications?
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Consequences of geometric errors in 3D city models
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1. for “simple” visualisation
2. for solar potential
3. for volume calculation
4. for advanced simulations
I ignore the semantic here
Solar potential
wrong orientation == no potential assigned
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Volume calculation
tiny problems == impossible to calculate
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Volume calculation
tiny problems == impossible to calculate
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Volume calculation
big problems == also impossible to calculate…
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Volume calculation
superstructures not topologically connected
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Volume calculation
superstructures not topologically connected
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Volume calculation
superstructures not topologically connected
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Advanced simulations
wind comfort for pedestrians
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Figure from CADFEM.de
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Advanced simulations
3D CFD methods: tetrahedralisation of volume
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computational fluid dynamics
Figure from CADFEM.de
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Advanced simulations
very strict input requirements
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Figure from CADFEM.de
• no holes
• no intersections
• triangles must have certain shape (no slivers)
• a “perfect” surface is thus required
• in practice, that still means several hours of
(semi-)manual repair
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Do current 3D city models
often contain these
geometric errors?
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tl;dl: YES.
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Our methodology
37 CityGML datasets from
9 countries
40 million polygons in 3.6
million buildings
(Solids + MultiSurfaces)
our software:
val3dity
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Summary of results
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• No CityGML dataset is 100% valid, not even LoD1
• Many simple errors, eg:
• repeated vertices
• non-planar polygons (most common error!)
• Notice that these are often not visible
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Summary of results
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• No CityGML dataset is 100% valid, not even LoD1
• Many simple errors, eg:
• repeated vertices
• non-planar polygons (most common error!)
• Notice that these are often not visible