a step toward interoperability: managing 3d urban data with gml

Andrea Scianna DIRAP – University of Palermo – Italy


Goals

This work is aimed to:

• definition of an interoperable and multi-scale cartographic model, both for urban planning and management of risk events, accordingto a national project (PRIN2004) titled ‘Evolution of cartography for GIS and WEB-GIS applications’;

• creation of GIS and WEB_GIS applications for management of group of public buildings (university campus, hospitals, sports ground, etc.) and related infrastructures.


Guidelines

Guidelines of whole national project are:

• finding best solutions to improve quality standards for numerical cartography in the Italian contest;

• defining criteria for generalization of multi-scale cartography;

• developing a model of 3D vector cartography;

• investigating methods for structuring numerical interoperable cartography, both for Internet Web applications and as traditional exchange format too;

• experimenting the application of the cartography structure on real cases study;

• writing a GIS model to be used either on commercial and open source software .


Methodology

Methodological approach is based on:

• the analysis of existing 3D GIS models;

• a comparison between the theoretical enunciation of different analyzed international models and applications actually derived from them.

On this basis, our model has been developed taking also in account some requirements of national traditional cartographic standards.

The new model comprises both the innovative aspects of interoperability, based on a structure with 3D contents, and more traditional thematic content with emphasis on aspects of urban planning and management of risk situations.


Methodological aspects3D cartographic

structure3D topological

structureImplementation

approach

Comparison between proposals

Analysis of someproposals

In Italy In Europe

Analysis of main3D topological models

Selection of a suitabletopological models

Analysis of 2Dtopological functionalities

Check of featuresof many formats

Analysis of filesstructure

Analysis of mainfunctions

Data managementin DXF, GML3, etc.

commercial open

Exchange formats Softwareimplementation

Selection of a fewGIS software

Identification of mainexchange formats

In Europe

Definition of a new cartographic model

At medium and large scale


Main steps

1. analyzing characteristics of the most diffused formats in Europe for geographical data interchange;

2. performing tests on different GIS software in handling DXF and GML, to investigate their capabilities to manage geometrical and topological structures, as well as 3D and geographical data;

3. analyzing various proposal for structuring numerical cartography;

4. definition of the cartographic model;

5. building of a software capable to handle geographical data, able to produce cartography, structured in GML 3 format;

6. building of a three-dimensional visualization software, that allows exporting and importing cartography in several formats (not started).


Is GML standard the answer to our needs?

• GML 3 is suitable to define 3D objects.• The structure can handle semantic data with respect to CAD

interchange format as DXF.• It is possible to structure information at different level of detail (not yet

implemented at this stage in our model).• GML files relating to the whole geographic database are very large, but

transferring of blocks of data with complex topological structure using streaming techniques is allowed.

• There are great flexibility and freedom in the implementation ofschemas, that however cause many problems about interoperability(saving and reading with existing GIS software is not always possible).

• Geospatial data encoded in GML format can be downloaded and uploaded from clients by multiple Web Feature Services.


Cartography requirementsNumerical cartography must satisfy a large number of purposes and it has to be provided with specific features to make it suitable for certain uses.

fundamental for the tasks that it

must accomplish to

Nominal scale

Topology support

Generalization

3D support

LBS support

data must be topologically structured to be used

or processed in advancedapplication

two types of generalization,

named “first level”

and “second level”

presence of thirddimension is useful

both for visualization and

analysis, for geoprocessing

and computation (like volume calculation,

visibility charts, cost's evaluation,

etc.)

the way to structure multiscale

cartography has a great influence over the creation

of LocationBased Systems


Main national Italian standard proposal, called “IntesaIntesa GIS GIS model” (IntesaStato Regioni Enti-Locali) has been examined: this cartographic model was written by a working group composed of several members of the main public Italian bodies.

Using this model it's impossible to directly define objects with three dimensions, or volumes: surface are represented in two dimensions only, but there is an “hybrid” way to model 3D surfaces, using a class of spatial attribute called “B3D surface”, that is constituted by a 2D surface joined with a 3D ring that is the boundary of the surface. Level of detail are not defined.

Analysis of existing models

“CityGMLCityGML” is another of examined model: it’s a very interesting cartographic model, mainly oriented to structure 3D models of cities.It is an application profile for GML3 which encodes a multi-level representation of cities, also including elevation, vegetation, water bodies, city furniture and more. Among its characteristics: the use of “Level of details”, that allows use of cartography from a medium to a building scale; topological rules joined with geometrical ones; use of textures (derived from X3D) whose definition is not present in GML standard.


After evaluation of existing models and cartographic needs, a model hasbeen defined in draft format: this model attempts to put together the requirement of old well-established rules (i.e. the ones coming from Commissione Geodetica Italiana) regarding a shared way of structuring entities of numerical cartography, and needs of three-dimensional visualization and analysis of urban and out-of-town landscape.

Definition of a cartographic model - 1

Classe02: Edifici pubbliciGruppo01: Perimetro Sottogruppo01: muro perimetrale esterno_1-5k02: muro perimetrale interno_1-5k03: dividente volumetrica_1k04: portico_1k05: linea di ingombro di scale esterne_1k06: cortili interni_1k07: …..……Gruppo02: CopertureSottogruppo01: linee perimetrali esterne dei tetti_1-5k02: linee perimetrali interne dei tetti_1-5k03: linee di falda dei tetti_1k04: lucernari_1k05: simbolo di inclinazione delle falde_1k06:…..….

Abstract of a first cartographic model derived from those onesof Italian Geodetic Commission and other italian model fornumerical cartography.

The model is hierarchically organized in classes, groups, sub-groups, and cover the most interesting geographical objectswhich are represented in a traditional analogical cartographyat medium and large scale. Classes defined in the model are railways, roads, buildings and artefacts, hydrography, vegetation, orography, administrative boundary.

To each feature class is assigned a code with four couple of numbers.

Besides this model is also organized to support a first simplygeneralization from 1:1000 to 1:5000 scale.



Feature class are grouped and linked into a schema that is splitted in different smaller schemas, depending on the main classes that are described as follows:

• vegetation: parks and gardens, rows of plants, single plants;

• utilities: networks and pipelines for carrying water, gas, electricity, etc.;

• orography: isohypses, spot heights, breaklines, natural shape;

• hydrography: rivers, lakes, sources;

• transportation infrastructures: roads, railways, undergrounds and their accessories (parking and depot areas, pavements, road axes, etc.);

• buildings: edifices and their accessories, set of buildings, other buildings (i.e. pylons, walls, etc.).


Definition of a cartographic model - 3Main features of this model are:• structure according to indication of rules coming from OGC and ISO 19100

series;• topological constraints defined together with the geometry;• features structured using 0, 1, 2, 3 dimensional primitives, with the constraint

that each higher primitive derives from the lower; • aggregate objects not defined;• edges composed by straight lines and planar faces;• orientation of faces stored explicitily, using the rule of the right hand;• terrain modelled using contour lines and spot elevations.

Topological schema of the modelModel derived from Kolbe and Groeger



UML Diagram of the “Construction” class



maximum_size

(3D face)

Crowning

(3D ring)roof

(3D oriented face)

wall

(3D oriented face)

ground_size

(3D face)

terrain-building_intersection

(3D ring)Representation of buildings elements


Definition of a cartographic model – 5-bis

Video-representation of an example model



cycle_path

street axis

parking

terrain-building_intersection

pedestrian

railway_area

Representation of three feature classes (raiways, roads, constructions)


Software implementation

In order to better reach the aims proposed, particularly regarding structuring cartography in accordance with the model defined, a software has been designed.

The software is implemented like an “ARX” (Autocad Runtime eXtensions) component, in AutoCAD environment.

It has been developed in C++ language, and it uses an mdb file as database to store information.

It can be used on many of recent versions of Autocad (100 % compliant with 2004, 2005, 2006 versions), including Autodesk Map too.


Software functionalities

After launching the application it is opened a popup window, with a multitabmenu structure essentially allows you:

- to define (“set” button) various components of a feature, like crowning, walls, roof, and so on, giving at the same time semantic attributes too and storing all them into an external database;

- to get information (“get” button) on single entities and on entities belonging to a particular feature, as defined above;

Today development concerns the capabilities to export so structured data in GML3 format, complying with our model, using a suitable application schema.

Subsequently a browser for this type of data will be implemented.


Software demo


Conclusions

The model will evolve when it will be used, but there are some important step in order to give life actually to the model. Some of them are:

• Browser implementation for 2D and 3D visualization in order to test the model for visual applications;

• Study the method to store objects’ updating;

• Studying methods to transfer 3D GML data in existing spatial database formats

• Exploring all the ways to query the model


University of Palermo CNR (National Research Council)

Italy

Thanks for your attention !

http://gislab.dirap.unipa.it

a step toward interoperability: managing 3d urban data with gml

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