A Data Model for Representing Cities in Three Dimensions · Models may be encapsulated as COLLADA...

Harvard UniversityGraduate School of Design

A Data Model for Representing Cities in Three Dimensions

Presented by Paul CoteESRI User Conference August 2008


AbstractThis talk will describe an ArcGIS Geodatabase model and model-builder toolkit for organizing and visualizing three-dimensional city models. This simple relational database schema provides means of organizing 3d model assets and retrieving logically consistent visualizations of the city at different time periods, proposed development scenarios, and at appropriate levels of detail. The presentation will discuss the extension of this model with reference to the emerging Building Information Spatial Data Model BIM Standards and CityGML.

2Paul Cote. ESRI UC 2008


Findings:

To build a data model for buildings, campuses and cities, requires that we build a schema to represent many different types of features that are inter-related. We should:

Avoid the usual home-grown, seat-of-the-pants problem solving strategy and participate in community-based data modeling work Anticipate the need to exchange data between different specialized software toolsEncourage our vendors to support community based data modeling efforts and vendor neutral formats for data exchange!



Acknowledgement

This work was made possible by funding by the Town of Brookline, Massachusetts Department of Management Information Systems. Feng Yang, Director.



Evolution and SustainabilityWe’ve seen plenty of demos, but how can we evolve our municipal GIS infrastructure to incorporate 3d building models that are a solid, sustainable part of our infrastructure? Sustainable evolution of municipal infrastructure will:

Make use of existing GIS layersBuild on the scalable relational (table-based) data structure of GISExtend GIS data models to deal with true 3d data Require interoperability with 3d modeling tools and new Building Information Modeling Tools

Reliable cross-vendor interoperability will depend on stable open interchange standards



Traditional layers in a municipal GIS infrastructure are two dimensional:

Property ParcelsBuilding FootprintsOrthophotographyEdge of PavementPhotogrammetric Contours

Today’s GIS Infrastructure



2.5 Dimensional Models From 2d GISHeight Information can be added to 2D GIS data to develop two and a half dimensional models for visualization

Buildings may be ExtrudedContours and Edge of Pavement may be turned into ground surface models as Triangulated Irregular Networks (TIN)Orthophotography or thematic information may be draped on surfaces



GIS as Basis for 3D Models

GIS tools like ArcGIS are not suited to making true 3d Models, but GIS information infrastructure is very useful as a basis for detailed 3d modeling.

Represents consistent, controlled geometry over broad areaProvides rough 2.5-D massing context



GIS -> 3D Modeling Interoperability

Transferring data (interoperability) between GIS and 3d Modeling tools has been a very difficult process until a few years ago.

Common CAD formats (DWG/DXF) does not pass information for extrusion

ESRI has no way of interchanging TIN information to DWG / DXF



Sketchup InteroperabilitySketchup is a 3d modeling tool that deals with georeferencing and interoperability with geospatial tools.

Capable of getting terrain with draped aerial photos from Google Earth or ArcGISCapable of getting extruded massing models from ArcGISVery rich capabilities for making 3d modelsModels may be encapsulated as COLLADA files COLLADA files may be dealt with as singular data objects in a database or Google 3d Warehouse

Vendors of 3d modeling tools are rushing to incorporate generic COLLADA import and export.



Incorporating true 3d models with GIS not only provides a rich visualization tool, but also a means of managing large collections of models.



Workflow for Developing City Model

Selection of Model Elements

Terrain, Massing, 3d BuildingsBased on Date or Scheme

Export to CAD or Rendering SystemRendering:

Hi Quality (e.g. 3d Studio)Web-Based (e.g. Google Earth)

Creating new model elementsUpload of new model elements to repository



Concern about Vendor-Specific Exchange Formats

Nobody should build an infrastructure that depends on vendor specific arrangements for interchanging proprietary data formats!

Despite the best intentions, interoperability may cease to work as software features changeCOLLADA is an exchange format maintained by a consortium (Khronos) that is regulated by a consortium of vendors, its specification is open and has stable well documented versions.At version 9.3 ArcGIS will be able to import a COLLADA file and convert it to its own 3d Data format (multipatch). YAY!


Harvard UniversityGraduate School of Design Paul Cote. ESRI 14

Vendor Neutral Exchange: COLLADACOLLAborative Design ActivityStandards Consortium:

Khronos GroupCommunities:

VisualizationGaming

Capabilities:Very rich visual and physical simulation: photorealistic shaders, cameras, movementNo semantic modelNo georeferencing

Modeling / EncodingUML / XML

Adoption:Many 3d authoring tools, 3d Studio, Sketchup …The vehicle for textured models in Google Earth


GIS Management of 3D Building ModelsThe availability of sketchup and the interoperability with Google Earth and ArcGIS is leading to the development of lots of georeferenced 3d building models. We need a systematic means of organizing these assets

Visualizing large models requires different levels of detail for distant or up-close rendering: Cities change, we need to be able to render temporal scenarios buildings based on year built and year demolishedNeed fictitious design schemes with proposed buildings and demolitions



Building Model Management Schema

Abstract BuildingsBuilding IDAttributes…

Massing Parts

Building ID

Part ID

Attributes…

Skin PartsBuilding ID

Part ID

Attributes…

SchemesScheme ID

Name

Scheme Parts

Scheme_IDPart IDRender

n

1

n

n

n

1 n

1

1



17

New Table: Abstract Buildings

Abstract BuildingsTerritory Cambridge

Building Cam_P364234_B0

Owner Harvard

Built Date 1870

Demo Date

Null

Address 49 Quincy St

Stories 5

The Parcels table can form a table of information about buildings. Unique Building IDs are created from Parcel IDs. This table has no geometry associated with it. Any building associated with a parcel are designated Building 0. This lumping is inaccurate, but sufficient for an initial buildings table.

B0

Cam_P364234


18

New Layer: Building Massing Parts

Building Massing PartsPart_ID Cam_P364234_B0_M1

Owner Null

Built Date

1998

Demo Date

Null

Address Null

Stories 2

B0_M0

Cam_P364234

Where individual building parts vary in terms of their attributes, they may be distinguished with unique IDs and individual build and demo dates, etc. The Building Massing Part IDs are formed by appending a Massing Part ID to the Building ID.

B0_M1


19

3d Building Massing Parts Model


Owner Null

Built Date

1998

Demo Date

Null

Address Null

Built Yes

Stories 2

B0_M0

B0_M1

The Massing Parts Layer forms a complete model of every building in the metro area at a low level of detail (CityGML LOD2). Building parts may have more specific attributes from their parent Abstract Buildings.


20

3d Building Skin Models

Building Skin PartsShape Multipatch

Model Sketchup or Collada Blob

Part_ID Cam_P364234_B0_S0

Owner Null

Build Date

1870

Demo Date

Null

Built Yes

B0_S0

Cam_P364234

Using a 3D authoring tool, models of building exterior skins can be encapsulated as sketchup or collada models and placed into relational tables as georeferenced objects. Like Massing Parts, Skin Parts have unique IDs linking them to abstract buildings and may have more specific attributes.


21

3d Building Skin Parts

Cam_P364234




Owner Null

Buid Date

2001

Demo Date

Null

Built Yes

B0_S1

Skin parts and massing parts for a given building may have independent dates. The Model field holds a Binary Large Object that can be downloaded to a 3d authoring tool for editing.


22

Built and Unbuilt Scenarios




Owner Null

Built Date

2001

Demo Date

Null

Built Yes

Cam_P364223_B0_S0

The Built attribute is set to Yes for buildings that were actually built. Unbuilt buildings can be represented in the schema to allow experimentation with proposed scenarios.


23

Built and Unbuilt Scenarios




Owner Null

Built Date

2001

Demo Date

Null

Built No

Cam_P364223_B0_S1

The Built attribute is set to Yes for buildings that were actually built. Unbuilt buildings can be represented in the schema to allow experimentation with proposed scenarios.


24

NullYear Demo

Abstract Buildings

5Stories

49 Quincy StAddress

1870Year Built

HarvardOwner

Cam_P364234_B0Building

CambridgeTerritory

Relational Queries Create Views Based on Dates or Scenarios

Building Skin PartsShape MultipatchModel Sketchup or Collada

BlobPart_ID Cam_P364234_B0_S1Owner NullBuilt 2001Demo Null

Built Yes


Owner Null

Built 1998

Demo Null

Address Null

Stories 2

Harvard UniversityGraduate School of Design Paul Cote, 2008 25

The Scheme View Tool

A tool has been created with all of the SQL to create the three views necessary to portray a Date and Scheme Specific Scenario based on the user’s privileges. One needs only to double-click on the tool and fill in the blanks.


26

Current Built View


27

1998 Historic View


28

Unbuilt Scheme: Turn Gund Hall Around


View From Proposed Design Scheme




Massing Parts

Building ID

Part ID

Attributes…


Part ID

Attributes…

SchemesScheme ID

Name

Scheme Parts

Scheme_IDPart IDRender

1

n

1

n

n

n

1 n

1

1


The Scheme View Tool

A tool has been created with all of the SQL to create the three views necessary to portray a Date and Scheme Specific Scenario based on the user’s privileges. One needs only to double-click on the tool and fill in the blanks.


Extending to Interior Spaces

This 3d Model Schema is compatible with the Penobscot Bay / ESRI data model for interior spaces.


This 3d Model Schema is compatible with the Penobscot Bay / ESRI data model for interior spaces.


Interior SpacesBuilding ID

Part ID

Attributes…

Paul Cote. ESRI



Massing PartsBuilding IDPart IDAttributes…


Part ID

Attributes…

1

n

1

n

n

n

Interior SpacesBuilding ID

Part ID

Attributes…

33


Expect Problems with Interrelated Models

Expect problems, and you will rarely be disappointed! What are some problems that we can expect with merging interior spaces with building exterior models

Opportunity for audience participation!



Building Information ModelsBuilding Information Modeling is essentially the application of GIS data modeling concepts to buildings.

Building information developed and used in Design, Construction, Facilities Operation, Demolition is integrated into a single modelMany tools are capable of creating and analyzing BIMThe ability to exchange information among these tools allows toolmakers to specialize and users to have a choice of tools



IFC

In order to have interoperability between the various specialized tools used in the Architecture Engineering, Construction and Facilities Management requires exchange of structured information.

The emerging exchange standard for interoperability in the BIM world is IFC: Industry Foundation ClassIFC is a stable, open specification of a consortium of vendors and large users of building data.Even though IFC is very thorough and complicated, simple profiles for interior spaces have been developed



Vendor Neutral Exchange: IFCIndustry Foundation ClassesStandards Consortium:

International Alliance for Interoperability (IAI BuildingSmart)

Communities: Architecture Engineering and ConstructionFacilities Management

Capabilities:Very rich semantic model for building systems and relationships

Modeling / EncodingEXPRESS / STEP, XML

Adoption: Very broad adoption in authoring tools for Building Information Modeling (BIM)Requirement for many big building customers e.g. U.S. General Services Administration


Harvard UniversityGraduate School of Design Paul Cote. ESRI

IFC Model Views may be Very Simple

Slide taken from NBIMS V1

38


Solution:

The makers of BIM authoring tools like Autodesk, Graphisoft and Bentley and others have implemented import and export of IFC for exchange of interior space data.

ESRI should make an IFC importer to populate the interior spaces model.BIM authoring tools should export COLLADA models of building skins at different levels of detail with attributes, ready for import into GIS data models.



More ProblemsWhat are some more problems that we can expect in integrating building models with other elements of city models?

Building models and terrain models need to meet each other at the right place witout awkward intersectionsWe need to model terrain at different levels of detailNeed to model vegetation at different levels of detail.Buildings and roads and other outdoor features have important relationships.Many different communities and specialized tools will be necessary to build these models.



Vendor Neutral Exchange: CityGMLCity Geographic Markup LanguageStandards Consortium:

Open Geospatial Consortium (Best Practice Specification)Communities:

PhotogrammetryMunicipal Geospatial Infrastructure (Mainly in Europe)

Capabilities:Very rich semantic model for city objects and relationships5 predefined levels of detailImage textures supported

Modeling / EncodingUML / XML / GML3 Profile

Adoption: Berlin, Bonn and many other German citiesCompatible with OGC Web Feature Services



CityGML is Adapted for Modeling Semantics of Observable Objects

Robot: Mobilerobots.com. Photo: DirectionsMagazine

www.aeromapss.com/lidar.htm

Paul Cote. ESRI UC 2008 42


CityGML: Engineered objects relate to various terrain surfaces

Image from OGC CityGML Discussion paper, Kolbe, Groeger, Czerwinski



CityGML: Objects May Honor Specific Levels of Detail




CityGML can provide a Spatially Exhaustive Semantically Rich model of the city




CityGML: Transportation Objects




Conclusion:

To build data models for buildings and cities, we will build a container for many different types of features that are inter-related. We should:

Avoid the usual home-grown, seat-of-the-pants problem solving strategy and participate in community-based data modeling work Anticipate the need to exchange data between different specialized software toolsEncourage our vendors to support community based data modeling efforts and vendor neutral formats for data exchange!



References and Resources

Demo Data and Full Documentation:http://www.gsd.harvard.edu/pbcote/research/brookline

Building Information Spatial Data Model:http://www.bisdm.org

Industry Foundation Classes (IFC):http://www.iai-international.orghttp://www.facilityinformationcouncil.org/bim/

City Geography Markup Language:http://www.citygml.org/

Contact: [email protected]


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