BIM, CityGML, and Related Standardization · 2 T. H. Kolbe – BIM, CityGML, and Related...

Department of Geoinformation Science

Technische Universität Berlin

1/6/2012

BIM, CityGML, and

Related Standardization

Thomas H. Kolbe

Director

Institute for Geodesy and Geoinformation Science

Berlin University of Technology

[email protected]

1st of June, 2012

Digital Landscape Architecture Conference 2012 in Bernburg/Dessau

2 T. H. Kolbe – BIM, CityGML, and Related Standardization


1/6/2012

Overview

Motivation: 3D information integration

data integration on the visualization level

data integration on the geodata level

Standardization of 3D geodata exchange

The different modeling approaches and paradigms

Computer graphics approach

AEC / CAAD / BIM approach

GIS approach

A short look at data formats (IFC, CityGML) / comparison



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City B

City Model

Level-of-Detail 1-3

City A

City Model

Level-of-Detail 1-3

Authority A (DTM)

Regional Model

Level-of-Detail 0

Company C

City Model

Level-of-Detail 3-4

Application Model

A B „Zonal

Fragmentation“ B

C

B

C C C

Application Model

„Layer

Fragmentation“

Internet /

Intranet

User

Provider

Key Issue: 3D Information Integration



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Different Stages of Information Integration

OGC Web

Feature Service

CityGML

OGC Web 3D

Service, WVS

VRML / X3D / KML

System A

Geodata

graphical

Elements

System B

Geodata

graphical

Elements

Geodata level

Visualization level

Web Client C



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Visualization Level Geodata Level

Interoperability on the geodata level requires

standardised base model and exchange format for

spatial (3D) objects e.g. ISO 191xx / GML3; ISO Step; XML

common application / information model (ontology):

consensus on terms, entities, their properties and relations, and: their meanings

conceptual schema and implementation schema

appropriate data services e.g. Web Feature Service

Interoperability on the visualization level requires

combinable graphical elements (3D geometries +

styling / appearance information) and interaction elements

standardised model and exchange format

for (3D-) graphical elements e.g. KML, X3D, VRML97, COLLADA

appropriate portrayal services e.g. W3DS, WPVS



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Standards are Key

for the integration / combination of (3D geo) data

from different data sources



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Who standardizes (geo)virtual 3D worlds?

Open Geospatial Consortium (OGC)

Exchange formats GML; CityGML; KML; Web Services: WFS, WTS, W3DS

buildingSMART Alliance (formerly called IAI)

Product model for AEC/FM: Industry Foundation Classes (IFC)

Web 3D Consortium (W3D)

Originator of VRML, GeoVRML, X3D

3D Industry Forum (3DIF)

Graphics format “Universal 3D“ (U3D) -> direct embedding in PDF

Khronos Group

Exchange format COLLADA (used within Playstation, Google Earth)

International “De Jure“ Standardisation: ISO

ISO standards of the 191xx family ( OGC Standards), X3D, IFC



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Standardization of 3D Geodata Exchange

Data formats

encoding of geometry, topology, appearance, and semantics

recent developments specify meta formats (e.g. GML3, COLLADA)

meta formats are only the basis or container model for the specification of user-defined application schemas

Application schemas

domain specific (semantic) modeling / ontology

result of a consensus process within an application community

are mapped to concrete data formats

examples: CityGML ( GML), IFC ( Step),

INSPIRE Data Specifications ( GML), ALKIS / ATKIS ( GML)

Data access & processing

Web Services (currently mainly by the Open Geospatial Consortium)

specific for 3D: data and visualization services (WFS & W3DS, WVS)



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Determining Factors on 3D Data Standards

Required or intended data characteristics / quality

details and structure of geometry, topology, semantics, and

appearance

scope and scale

Original application domain in which a standard is

being developed (AEC, GIS, Simulation, Gaming)

determines the 3D modeling paradigm; also affects the scale

Intended applications

e.g. visualization only; environmental or training simulations;

facility management, complex spatio-semantic analyses

Type of usage (stand-alone, linked to/over the web)

Type of access (filesystem based, web services)



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Elements of (3D) Spatial & Semantic Modeling

Geometry

Topology

Da

ta m

od

elin

g

Me

tad

ata

Appear-

ance

Semantics

• themat.

structure

„(Geo)Spatial Information Modeling“



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3D

Approaches to 3D City / Landscape Modeling

Computer Graphics

Scene Graphs

Geospatial / GIS

(Semantic) City and

Landscape Models

AEC / CAAD

Building Information

Models

Computer Games /

Simulation

Simulation and

Interaction Models



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Computer Graphics Approach

Real world Abstraction wrt. visual characteristics 3D model

Only visible elements and properties of objects are relevant

restriction on geometry and graphical appearance

efficient visualization; modeling of graphical characteristics

scene graph models (B-Rep + primitive instancing)

typically no consideration of object semantics



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Computer Graphics Approach

What is modelled?

geometry (parametric primitives; boundary representation)

material / appearance

typically no semantic information; limited topology

interaction methods and object behaviour

all elements are structured within scene graphs

elements have local 3D coordinates (mostly in Euclidean CS)

aggregation using group nodes; transformation nodes

allows to define prototypes / reuse object definitions

some exchange formats support georeferencing

GeoVRML, X3D, KML, COLLADA (from V1.5), OpenFlight

but: models often are restricted to one coordinate system (type)



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Underneath the surface…

Computer graphics models are generated predominantly for the

„nice“ (often realistic) and efficient visualization

only visible parts are trustworthy!

Wire frame visualization

dormers are extruded

through the whole building

Textured visualization

visualization does not reveal over-lapping building and dormer bodies



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AEC / CAAD Approach

Buildings Abstraction on design (plans) Real world

Mapping of the constructive elements

component oriented modeling:

Constructive Solid Geometry (CSG)

Building Information Modeling: Semantic objects with geometries



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AEC / CAAD Approach

What is modelled?

geometry (parametric primitives; boundary representation;

constructive solid geometry; sweep volumes)

topology

limited material / appearance

explicit semantics within building information models (BIM)

(but not with legacy CAD formats like DXF)

Most important BIM exchange format is IFC (Industry

Foundation Classes)

IFC defines a product data model for buildings / sites (only)

Elements of a BIM dataset are aggregated within a project

BIM / CAAD models have very limited support for georeferencing

models are restricted to an Euclidean, cartesian coordinate system



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Geospatial / GIS Approach

Real world Topographic abstraction Surveying

generally, only the object surfaces are observable:

Boundary representation (B-Rep)

Points and surfaces are surveyed / registered using sensors

Urban Information Modeling: Semantic objects with geometries



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Geospatial / GIS Approach

What is modelled?

geometry (3D in ISO 19107: only boundary representation)

topology

semantic information

limited appearance / material properties

Models are based on the notion of geographic features

(according to ISO 19109); exchange format is GML

Application schemas define ontologies, i.e. taxonomies

and partonomies of feature types (using OO concepts)

Ontology for 3D city models: CityGML

always georeferenced; any 3D coordinate reference system

(CRS) can be used (and mixed within the same dataset)

all geometries must belong to a CRS; nesting is possible



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Differing Modeling Paradigms

Volumetric, parametric primitives

representing the structural components

of buildings

IfcWallStandardCase

IfcBeam

IfcSlabIfcWindow

BIM (e.g., IFC) Constructive Solid Geometry

Accumulation of observable surfaces of

topographic features

WallSurface

InteriorWallSurface

FloorSurface

IntBuildingInstallation

GroundSurface

Window

3D GIS (e.g., CityGML) Boundary Representation



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Differing Modeling Paradigms

Volumetric, parametric primitives

representing the structural components

of buildings

IfcWallStandardCase

IfcBeam

IfcSlabIfcWindow

BIM (e.g., IFC) Constructive Solid Geometry

Accumulation of observable surfaces of

topographic features

WallSurface

InteriorWallSurface

FloorSurface

IntBuildingInstallation

GroundSurface

Window

3D GIS (e.g., CityGML) Boundary Representation

Well suited to

support (generative)

design processes,

hence, to create

models for

planned objects

Well suited to

support model

generation from

surveying /

observation,

hence, to create

models for existing

objects



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3D Standards / Data (Exchange) Formats

Differentiation between general purpose exchange

formats and information model standards

General purpose: X3D, VRML, U3D, COLLADA, KML, GML,

Shapefiles, DXF, OpenFlight

Information models: CityGML, IFC

Different categories / fields of origin

CG / VR / Simulation: X3D, VRML, U3D, COLLADA, OpenFlight

Geospatial / GIS / UIM: Shapefiles, KML, GML, CityGML

AEC/FM / CAAD / BIM: IFC, DXF

The expressivity of a standard limits its representation

capabilities (important wrt. prevention of information loss)

Complementary use of GIS, AEC, and CG standards!



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Industry Foundation Classes (IFC)

ISO standard 16739 for semantic site/building models

developed by the buildingSMART Alliance

representation of site / building models with respect to

their geometry, topology & semantics

comprehensive 2D & 3D geometry support: B-Rep, CSG, Sweep

integrates diverse crafts; incl. material & cost calculations

most used and most comprehensive data model and

exchange format for Building Information Modeling

no representation of (graphical) appearances,

simple georeferencing (starting from IFC 2.3)

exchange format is based on STEP; ifcXML is

an XML-based mapping



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City Geography Markup Language – CityGML

Application independent Geospatial Information Model

for virtual 3D city and landscape models

comprises different thematic areas

(buildings, vegetation, water, terrain,

traffic, tunnels, bridges etc.)

Internat‘l Standard of the Open Geospatial Consortium

V1.0.0 adopted in 08/2008; V2.0.0 adopted in 3/2012

Data model (UML) + Exchange format (based on GML3)

CityGML represents

3D geometry, 3D topology, semantics, and appearance

in 5 discrete scales (Levels of Detail, LOD)



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Semantic 3D City Model of Berlin

>550,000 buildings;

• fully-automatically generated

from 2D cadastre footprints &

airborne laserscanning data.

• textures (automatically

extracted from aerial images)

• semantic information (includes

data from cadastre)

• 3D utility networks from the

energy providers

• modeled according to CityGML www.virtual-berlin.de

© NIBS 2007

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are needed to see this picture.26

Scope of Real Property Industry IA

I-IFC

Usag

e

Space

Natural Asset

Linear Structure

Structure

Building

Facil ity / 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 aTIFF (LZW) decompressor

are needed to see this picture.

City

GM

L

http://www.gsa.gov/Portal/gsa/ep/home.do?tabId=0



3D City/Landscape Model Exchange Formats

X3D COLLADA KML Shape CityGML IFC DXF

general purpose / information model gp gp gp gp im im gp

3D geometry + + + ++

georeferencing + + ++

appearance ++ ++ +

3D topology + +

semantics ++ ++

levels of detail + + ++

links/embedding + ++ ++ ++

extensibility + ++ + ++

fast rendering ++ ++ + + + /+ +

Legend: = basic, + = sophisticated, ++ = comprehensive; empty = not supported

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Summary

A range of 3D standards is available

concerning 3D data models and data exchange formats

concerning web services for data access, registry & visualization

Data standards differ significantly wrt. expressivity and

modeling paradigms geometry, topology, appearance, semantics

Facilitation depends on general application needs exchange of 3D presentations / visualization results versus

exchange of geospatial information, i.e. semantic models

CityGML and IFC model real world objects with specified

semantics (and spatial characteristics, of course) but with different scope, scales, and advantages

BIM, CityGML, and Related Standardization · 2 T. H. Kolbe – BIM, CityGML, and Related...

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