Introduction to CityGML

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Department of Geoinformation Science



Technische Universität Berlin

2009/05/19

Introduction to CityGML

Thomas H. Kolbe

Alexandra Stadler


Chair of Geoinformation Methodology

Institute for Geodesy and Geoinformation Science

Berlin University of Technology

{ kolbe | stadler }@igg.tu
-
berlin.de


19th of May, 2009

EduServ7 Pre
-
Course Seminar in
Ås

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Copyright notice:

This is copyrighted material. It is not allowed to
distribute copies or parts of these slides and the video
clips without the written consent of the author.

Please note, that the presentation also contains third
-
party copyrighted material used with permission.

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CityGML Tutorial

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2009/05/19

Overview


Introduction: Urban Information Modelling


CityGML overview and status


CityGML details


Extending CityGML


Application examples


Summary

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2009/05/19

Urban

Information

Modelling

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Applications of Virtual 3D City Models

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

3D City Modelling

… is far more than

the 3D visualization

of reality


In fact, the
geometry

and its
appearance

are
only one aspect

of an entity!


Key issue:

Semantic Modelling


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CityGML Tutorial

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2009/05/19

Prospects of Semantic 3D City Models (I)

Query your 3D city model!

(Possibly even without 3D
visualization)


From which windows in which rooms of which buildings do I
have visible coverage of a certain place, road, or monument?


What is the best position for a new transmitter station such that
the propagation of the radio signal is optimal?


To what floors have all buildings in a flooded area been
affected?


Where are audience halls in a specific area of the town (or on
the campus) with more than 500 seats, 3D projection capabilities
and less than 15min to walk from a public transport stop?


Urban Data Mining, 3D cartography

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Example for 3D Label Placement & Symbols

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

3D Label Placement for Augmented Reality

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Information Hub


Ongoing virtualisation

of our environment


Semantic models

of all relevant
objects in urban space


Base models

include most
important feature classes and
attributes


Objects may have several
geometrical representations


Spatial reference

links data of
different disciplines, since they
refer to the same physical space



base model entities

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Prospects of a Common Ontology


Data providers (e.g. municipalities) create 3D models with
a
defined information level
, which they can be sure will
be
required or useful for a wide range of applications


this in turn
makes it feasible / profitable

for companies to create
more advanced applications

that exploit semantic information



Applications can
rely on a specific data quality


thematic and spatial
structure and


(a minimal set of thematic)
properties

of the geo
-
objects

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T. H. Kolbe, A. Stadler


CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Information Modelling at Different Scales


Model content, structure, and employed

modelling principles depend on


Scale


Scope (application contexts)

Taken from the Homepage of the Helmholtz Research Center Karlsruhe, © Karl
-
Heinz
-
Häfele

© NIBS 2007

QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
13

Scope of Real Property Industry

IAI
-
IFC Usage

Space

Natural Asset

Linear Structure

Structure

Building

Facility / Built

Theatre / World

Sub
-
Systems

System

Level

Site

Real

Property Asset

Country

State / Province

County

Installation /

Region

Node

Segment

Room

Space

System

Level

Sub
-
Systems

Room

Water / Sea

Land / Parcel

Underground

Air / Space

Overlay

Overlay

Components

Components

City

QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
CityGML

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Overview & Status

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Requirements for 3D City Modeling


Geometric

and
radiometric

modeling


3D Coord. Reference Systems (3D or 2D+1D / geo. or proj.)


Topology


Semantic modeling / Object classification


Distinct thematic models /
feature types

with thematic attributes

(DTM, Buildings, Transportation, Water bodies, Vegetation, etc.)


Common information model / standardized data model


Different but well
-
defined granularities

/ abstraction

levels


Multi
-
scale modeling; support for generalisation


Support for the
integration
of different datasets

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T. H. Kolbe, A. Stadler


CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Requirements for 3D City Modeling


Geometric

and
radiometric

modeling


3D Coord. Reference Systems (3D or 2D+1D / geo. or proj.)


Topology


Semantic modeling / Object classification


Distinct thematic models /
feature types

with thematic attributes

(DTM, Buildings, Transportation, Water bodies, Vegetation, etc.)


Common information model / standardized data model


Different

but

well
-
defined
granularities

/ abstraction

levels


Multi
-
scale modeling; support for generalisation


Support for the
integration
of different datasets

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T. H. Kolbe, A. Stadler


CityGML Tutorial

Department of Geoinformation Science



2009/05/19

CityGML


Modelling Urban Spaces

Content


Data model and exchange format for virtual 3d city models


GML 3 application schema


Modelling of all relevant parts of the virtual city according to their

semantics
,
geometry
,
topology

and
appearance


XML

ALKIS ATKIS

[NAS]

...

CityGML

GML

ISO 191xx

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

CityGML Development


Developed since 2002 by the Special Interest Group 3D (NorthRhine
Westphalia, Germany)


Members from >70 companies, municipalities and research institutes


Adopted as international OGC standard since 08/2008


Application backgrounds

of the participants


Cadastre and Topographic Mapping


Urban Planning


Building Information Modelling, AEC/FM


Mobile Telecommunication


Environmental Simulation


Training Simulation and Car Navigation


Tourism and City Business Development


Geoinformation and Computer Science


(at its beginning) Real Estate Management

Broad

spectrum

of different

modeling

requirements

Good base

for a

multi
-

functional

standard

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Details

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Modularisation

CityGML consists of


a
core module


several
extension modules




癥v瑩捡c 獵bdi癩獩on

CityGML Core
GML 3.1.1
Building
CityFurniture
CityObjectGroup
LandUse
Relief
Transportation
Vegetation
WaterBody
Appearance
Generics


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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Coherence of semantics and geometry



Semantic object

e.g. Building

Associated geometry

e.g. Solid




Use of
Boundary Representation

(B
-
Rep) for geometry
modelling


Explicit relations between semantic objects and their
geometrical representations

*

*

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Department of Geoinformation Science



2009/05/19

„Availability“ of semantics

CityGML
: (Up to) Complex objects with structured geometry

Semantics

Geometry


Geometric entities know
WHAT

they are


Semantic entities know
WHERE

they are and what their
spatial extents are

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Thematic Modelling in CityGML

ExternalReference


-

informationSystem: anyURI


-

externalReference:


ExternalObjectReferenceType

Relief

Feature


loD1Geometry


loD3Geometry


loD2Geometry

Geometry

<<FeatureCollection>>

CityModel

_Vegetation

<<Feature>>

_CityObject

_Site

_Water
Bodies

_City
Furniture

_Transpor
-
tation

Objects

CityObject

Group

*

*

*

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Multi
-
scale modelling: 5 levels of details

LOD 4


Interior model

„Walkable“ architectural models

LOD 3


City / Site model

Detailed architectural model

LOD 2


City / Site model

Explicit roof structures

LOD 1


City / Site model

„Block model“ without roof structures

LOD 0


Regional model

2.5d Digital Terrain Model

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Digital Terrain Models

DTM for each Level of Detail can be composed of


TINs

(Triangulated Irregular Network),
Grids
,

3D Breaklines
, and
3D Mass Points



Each DTM component may be restricted to be valid in a
specific region by providing a
validity extent

polygon



Validity extent

polygon can
have holes

which allow

nested DTMs!

coarse

Grid

detailed

TIN

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2009/05/19

Digital Terrain Model: UML Diagram

MassPointRelief

BreaklineRelief

City

Object

gml:TriangulatedSurface

_ReliefComponent

+ lod: integer [1]

gml:

MultiPoint

gml:

MultiCurve

gml:

Polygon

TIN

Relief

ReliefFeature

+ lod: integer [1]

extent

1

1

1

0..1

gml:GridCoverage

1

*

Raster

Relief

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CityGML Tutorial

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2009/05/19

Example for a Nested DTM

Image: PhD work of G. Agugiaro, TU Berlin

Embedding of a high resolution DTM from Archeological Excavation

Hole within the validity
extent polygon of the low
resolution surrounding DTM

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CityGML Tutorial

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2009/05/19

Example for a Nested DTM

Image: PhD work of G. Agugiaro, TU Berlin

Embedding of a high resolution DTM from Archeological Excavation

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CityGML Tutorial

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2009/05/19

Building Model


Coherent aggregation of spatial and

semantical components


(recursive) composition of
building parts


thematic surfaces

(roof surface,

wall surface, etc.) [from LOD2]


building installations

like dormers, stairs, balconies [from LOD2]


openings
like doors and windows [from LOD3]


rooms

and
furniture

[in LOD4]


Components contain relevant
thematic attributes


name, class, function, usage, construction and demolition date,
roof type, address


no. of storeys above / below ground, storey heights

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CityGML Tutorial

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2009/05/19

Building Model in LoD1: UML Diagram


loD1Solid


Solid

Geometry

Address

+ zipCode: int

+ city: String

+ street: String

+ houseNumber: String

0..*

1

BuildingPart

_AbstractBuilding


+ function: BuildingFunction[0..*]

+ yearOfConstruction:integer[0..1]

+ roofType: RoofType[0..1]

+ measuredHeigth: LengthType[0..1]

+ …

Building

0..*

0..1

Implemented in
CityGML using the
xNAL standard from
OASIS

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2009/05/19

Building Model in LoD2


loD1Solid


loD2MultiSurface


loD2MultiCurve

Surface

Geometry

Line

Geometry

loD2MultiSurface

_CityObject

_BoundarySurface

RoofS.

WallS.

GroundS.

ClosureSurface


loD2Solid

Solid

Geometry

_AbstractBuilding


+ function: BuildingFunction[0..*]

+ yearOfConstruction:integer[0..1]

+ roofType: RoofType[0..1]

+ measuredHeigth: LengthType[0..1]

loD2Terrain

IntersectionCurve

LoD1

LoD2

exterior

Building

Installation

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2009/05/19

Building Model in LoD3+4

loD4Multi
-

surface


loD4Solid

loD4Solid


interior

Building

Furniture

interior

interior

Room

LoD4

CeilingS
.

Interior

WallS.

FloorS.

RoofS.

WallS.

GroundS.

Closure

Surface

loD3Multi
-

Surface

LoD3

Window

Door

Opening

exterior

Building

Installation


loD3Solid

Solid

Geometry

_Abstract

Building

LoD1

LoD2

_BoundarySurface

Surface

Geometry

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2009/05/19

Building in LoD4


Interior Model

Entrance door

„Hallway“

„Back room“

„Living room“

Doorway

(with door)

Passage

(w/o door)


Topology implies Accessibility Graph !

Rooms

Can be used e.g. for
escape route

planning in disaster
management or

for mobile robotics

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2009/05/19

Spatio
-
semantical Composition

Building

BuildingInstallation
(Dormer)

BuildingPart

BuildingPart

Building

Building surface
(WallSurface)

3D
-
Modell: Stadt Coburg

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CityGML Tutorial

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2009/05/19

Spatio
-
semantical Coherence (I)

MultiSurface

(„MultiPatch“)

Surface

Surface

Geometry

Semantics


1st case:
structured / unstructured geometry only, possibly
along with appearance properties


typical models based on 3D graphics formats like VRML,

X3D, KML, U3D or legacy CAD geometry formats


usable (in fact tailored) for visualizations; simple visibility
computations

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CityGML Tutorial

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2009/05/19

Spatio
-
semantical Coherence (II)

MultiSurface

(„MultiPatch“)

Surface

Surface

Building

Geometry

Semantics


2nd case:
simple object with unstructured geometry


identifiable objects with a set of simple thematic properties

(this is the modeling capability level of e.g. Shapefiles)


typical result of (current) photogrammetrical registration systems


usable für visualizations & simple thematic queries; simple visibility
computations

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Spatio
-
semantical Coherence (III)

Geometry

Semantics

Composite
-

Solid

Solid

Solid

Surface

Surface

Building


3rd case:
simple object with structured geometry


typical result of 3D modelling tools, but also from (a few)
photogrammetrical registration systems

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CityGML Tutorial

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2009/05/19

Spatio
-
semantical Coherence (IV)

MultiSurface

(„MultiPatch“)

Surface

Surface

Geometry

Semantics

Building


House

Garage

Stairs

WallSurface

RoofSurface


4th case:
complex object with
unstructured geometry


Data is typically derived from
Building Information Models like
IFC or retrieved from Facility
Management

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2009/05/19

Spatio
-
semantical Coherence (V)

Composite
-

Solid

Solid

Solid

Surface

Surface

Building


House

Garage

Geometry

Semantics

RoofSurface


5th case:
spatio
-
semantical coherently structured object


Highest quality level; can be obtained e.g. by careful derivation

from Building Information Models like IFC

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

External references

Objects may


Refer to their original data sources


Refer to other external data sources containing additional
data, e.g.


Building: Link to cadastre, information about owners


Door: Link to facility management systems


Antenna: Link to mobile communication databases

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2009/05/19

Appearances


Materials (similar to X3D)


Textures


Standard textures (explicit texture coordinates)


Aerial images (georeferenced)


Projected photos





Multiple appearances (
themes
) per object





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CityGML Tutorial

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2009/05/19

Georeferenced Textures

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CityGML Tutorial

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2009/05/19

Further CityGML Concepts


Support for
Topology


Shared geometric primitives can be referenced using XLinks


Support for
generalization of 3D data


Generalized objects are linked to the original objects on the
larger scale


Support for spatial homogenization / integration


e.g.
Terrain Intersection Curves

(for integration of 3D
objects with the terrain)

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CityGML Tutorial

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2009/05/19

Extending

CityGML

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CityGML Tutorial

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2009/05/19

Application Specific Extensions to CityGML


CityGML is considered a
base or core information
model

for virtual 3D city models


But:

Specific applications need specific extra information


typically in close interaction with CityGML base information


Examples


Environmental simulations

like noise immission mapping need
information about noise absorption of surfaces


Cultural heritage

needs to augment objects by their heritage and
history, and has to consider the development along time


Utility networks

need to represent pipes, pipe tunnels,
connectors, transforming devices

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2009/05/19

Extending CityGML

1.
Generic Attributes

& GenericCityObjects


every
CityObject

can have an arbitrary number of
extra attributes


allows to augment objects like Buildings, Roads, etc.
without the need of new application schemas


GenericCityObjects

can have arbitrary geometries
(and generic attributes) for every LOD


“extension during runtime“

2.
Application Domain Extensions (ADE)


extra XML schemas referring to the CityGML

XML schema (defined by
information communities
)


extensions to be
formally specified in XML schema

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2009/05/19

Generic Objects and Attributes


Simple to use extension mechanism


GenericCityObject

is used as
proxy

to model and
exchange features which are not provided by CityGML


Generic Attributes

can be used to establish (informal)
application specific
property

sets
for feature types



Some disadvantages


No further semantic structuring of generic objects and
attributes


Possible naming conflicts


Limited number of predefined attribute types:

integer, double, string, date, URI

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2009/05/19



<Building gml:id=“Building0815">




<!
--

generic attributes
--
>





<
stringAttribute

name
=“
BuildingOwner
">





<
value
>
Mr. Smith
</
value
>




</
stringAttribute
>





<
doubleAttribute

name
=“
Value
">





<
value
>
3500000.0
</
value
>




</
doubleAttribute
>





<!
--

specified properties of feature type “Building”
--
>





<lod2Solid> ... </lod2Solid>




<
/
Building>

Example for Generic Attributes

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2009/05/19

Application Domain Extensions (ADE)


Information Communities

should be able to define
extensions on their own


they must be able to associate new attributes to concrete
CityGML feature types


formal definition of new properties / feature types in XML schema


similar situation to the specification of GML application schemas


Different extensions should be usable

simultaneously


e.g.

CityGML

Building features augmented both by properties
from real estate and noise pollution simulation


Requires
combinable application schemas


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CityGML Tutorial

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2009/05/19

Example of application specific attributes

Example

for a CityGML
Building feature with

application
specific
extra information
(qualified by extra namespaces):



<Building>



<function>1000</function>


<lod2Solid> ... </lod2Solid>



...



<noise:
immissionPoints
>



<gml:MultiPoint> ... </gml:MultiPoint>


</noise:
immissionPoints
>


<noise:b
uildingHabitants
>8</noise:
buildingHabitants
>


<realEstate:value









currency=“EUR“>400000</realEstate:value>

</Building>

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Application Domain Extensions (ADE)


Well
-
defined mechanism to extend CityGML with application
specific information


Additional spatial and non
-
spatial properties, relations, associations,
new feature types


Semantic and geometric structuring follows the data needs


ADE hooks allow for augmenting the predefined CityGML features


No formal standardization process needed



Specification within their own XML Schema


Allows for XML validation of ADE enriched documents


Ensures semantic and syntactic interoperability


Globally unique XML namespace prevents naming conflicts


ADEs can be used simultaneously within one instance documents

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2009/05/19

CityGML

ADEs

Application Domain Extensions (ADE)

XML

NoiseSimul.

Disaster

management

ALKIS ATKIS

[NAS]

...

. . .

CityGML

GML

ISO 191xx

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CityGML Tutorial

Department of Geoinformation Science



2009/05/19

ADE implementations

ADE

Application domain

Proposed by

NoiseADE

Noise pollution simulation

SIG 3D

SubsurfaceADE

Underground features,
e.g. tunnels

SIG 3D

CAFM
-
ADE

Computer Aided Facility
Management

TU München

HydroADE

3D flood simulation

HFT Stuttgart

BridgeADE

(under development)

Comprehensive model for
bridges

SIG 3D

UtilityNetworkADE

(under development)

Utility networks, e.g.
water, electricity

SIG 3D

Available CityGML ADEs (excerpt)


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2009/05/19

Application

Examples

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2009/05/19

The Official 3D City Model of Berlin

www.3d
-
stadtmodell
-
berlin.de

3D visualization

is the result of

a portraying

of Berlin‘s

3D city model


(modeled

according to

CityGML)

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2009/05/19

Noise immision mapping

EU Directive: Minimisation of noise immissions


Calculation of noise immission maps for whole North Rhine
-
Westphalia


Data provision and exchange via CityGML using web
services (WFS, WCS, WMS):


8.4 million 3d buildings in LOD 1


3d street network in LOD 0, with additional noise related attributes


3d rail network in LOD 0


3d noise barriers in LOD 1


Digital terrain model (10 meter resolution)

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2009/05/19

Noise immision mapping

Noise immsion maps

reported to EU (via WMS service)

Noise immision simulation

3d geodata in CityGML as input for the
calculation of noise immision maps

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Department of Geoinformation Science



2009/05/19

Homeland security

Testbed OWS
-
4

of the Open Geospatial Consortium (OGC)


Setting:

Explosion of a „dirty bomb“

in the New York harbour


Task:

Support the planning committee

in the construction of an

emergency hospital


Find the appropriate location


Identify best fitting existing building (size, room layout, air
conditioning for decontaminations, etc.)


Thematic queries & visual inspections


Link different web services and client applications


Data formats:
CityGML

and
IFC

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2009/05/19

Homeland Security


CityGML building visualised using LandExplorer


from outside (left)


room
-
based representation of the security level (right)

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2009/05/19

http://www.opengeospatial.org/pub/www/ows4/index.html

Homeland Security

61

T. H. Kolbe, A. Stadler


CityGML Tutorial

Department of Geoinformation Science



2009/05/19


Coming to the end…

62

T. H. Kolbe, A. Stadler


CityGML Tutorial

Department of Geoinformation Science



2009/05/19

Summary

CityGML is a


Geospatial Information Model

(based on ISO 191xx)


and
Exchange Format

for virtual 3D city and regional
models (implemented as GML3 Application Schema)

CityGML represents

Geometry, Topology, Semantics, and Appearance


esp. semantic / structural information is needed for a range
of applications


gives city model data enough space to „grow“ with respect


to geometric, radiometric, and semantic contents & complexity


to semantic qualification / interpretation


to geometric / topological correctness

63

T. H. Kolbe, A. Stadler


CityGML Tutorial

Department of Geoinformation Science



2009/05/19

What is CityGML‘s Use for Research?


Base model

/ base ontology for


geodatabase developments


project specific extensions (like relations or new feature types)


Could be
target model

of 3D extraction methods


concerning feature types, aggregation structures


5 discrete scales usable for 3D generalisation


Exchange format


lossless information exchange between subsystems / GeoDB


increasing number of available implementations / 3D
-
GeoDB


Good amounts of
real testdata available


Berlin, Bonn, Bochum, Hamburg, Stuttgart, Recklinghausen, …


also 3 freely accessible Web Feature Services delivering CityGML

Department of Geoinformation Science



Technische Universität Berlin

2009/05/19

Introduction to CityGML

Thomas H. Kolbe

Alexandra Stadler


Chair of Geoinformation Methodology

Institute for Geodesy and Geoinformation Science

Berlin University of Technology

{ kolbe | stadler }@igg.tu
-
berlin.de


19th of May, 2009

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-
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