the 3D structuring cartography in GML3 to support interoperable generation, distribution and condivision
on network of GeoDataBases.
The work it has been articulated, in a first phase of methodological analysis, in order to characterize the existing standard that can
be used to improve the quality requirement of the cartographic structure.
Particulary beggining from legislative reference points such as: the detailed lists of written up content of the Technical Committee of
Intesa Stato Regioni for the contents of the GeoDatabase, the ISO TC/211 normative for the standardization criteria, the documents
about the use of XML/GML and the Open Gis Consortium (OGC). It has been therefore predisposed homogenous cartographic data
and it has been verified their quality about the previous standard; particularly it has been analyzed the follow aspects: the definition
of geometric-semantic congruence and coherence, and the definition of the 3D information data.
Subsequently, from this technical specifics, it has been investigated the translation in formal contents, using an owner interchange
software (ESRI), to support some guide lines implementations to generate a GIS3D structured in GML3.
The research focused on conceptual models such as spatial and logic relationship, typologies of geometric object and the ties and
relations between the objects which allows to define a geometric structure based on topologic proprieties.



1
. INTRODUCTION

Codifying and uniforming informatic data is one of two bigger
problems for data producers and employers. Therefore, also the
field of geographic information shows its proper needs of
uniformity and interoperability among different types of data.
In particular in the cartographic field, it has been moved from
the traditionally paper-drawn cartography to a numerical one
and then to the management of structured topographic
DataBase. From this moment on, we have the need to solve the
problem of the physical structure of the dataset.
In fact, even if DXF and DWG format is universally known for
numerical cartography diffusion, the same format is inadequate
to transferring data in the new form of GeoDatabase.
Therefore, Open Gis (OGC) Consortium has developed the
Geography markup Language (GML), apposite to memorize
and transfer ( via Web too) geographical data.
Thanks to this new language, various actors could share samely
codified data even if very heterogeneous inside themselves
because of the different interface software and owner data
structure.
At the same time, users should be able to have a transparent
access to all data structures developed by software employer, in
which the sequence string program has to remain at a higher
level: for the next future we cant imagine to teach to all the
users to program in XML language and in GML language to
generate a base GIS. The research in the future will be
implemented to create an elementary graphic interface to filter
the string even in case of complex 3d data structure.
1.1

Intro to GML

The Geography Markup Language (GML) is a specific
language, based on XML eXentisible Mark-up Language
coding, to memorize and transfer geographical data. GML has
been formuled in accord with the data conceptual model
traced and defined by ISO 19100 specific.
XML technology, very diffused today, can memorize and
represent data in a very flexible way, according to a proper
syntax, completely independent from the data producer.
An essential property of XML standard is the capability to
distinguish the content from its layout, so that the coding refers
exclusively to data structure.
So, GML, as every XML encoding, records geographical data in
a textual form, indipendently from their visual outcoming. Any
user can read these documents, so that using and modifying the
given data is therefore easy.
Gml is based on geographic data model developed by OGC.
This model describes the reality like geographical entities called
features; the feature is a finished list of properties and
geometrical elements.
The properties (attributes) are usually composed by a name, a
type and a value. The geometric properties are composed by
elementary entities defined at base level from: points, lines,
curves, surface and polygons.
The particular structure of this language allows to model even
complex objects: in this way, an articulated structure like an
airport can be codified through the set of simple object, such as:
the terminal, the runway, the car ways and the pedestrian ones.
KEY WORDS: Cartography, Digital mapping, Gis, GML, Interoperability ________CIPA 2005 XX International Symposium, 26 September 01 October, 2005, Torino, Italy________
The basic concept of GML is the feature which is an abstraction
of the reality phenomena and components.
As the result, all the elements in which the reality is composed
can be explained through set of different features: particularly a
geographic feature is a feature to which is associated a position
on the Earth.
A property of the GML is the possibility to group all the
elements with similar characteristics. These data structures are
specified in the GML Application schema which is a particular
XML grammar developed to describe the structure and the
contents of the XML documents.
At an advanced level there is the GML Schema which establish
the concepts and the construction used in all the application
field.
Lot of these elements implemented inside the XML Schema of
the GML base schema are object type defined in the specific
ISO 19100. The GML base schema establishes a set of pre-
defined schema and object which can be used inside the GML
Application schema.
To describe a specific geographic model trough GML an
Application schema has to be created extending or limiting the
data type defined inside the GML Base schema. For these aim
it can be used elements and attributes as defined inside the
GML Base schema.
The Application schema, as said, is of use to validate the GML
document and to define the data structure, and it can be built
using a text editor or specialized software in the XML schema
editing. In practice using the GML schema as conceptual
language it can also be translated directly the XML from a
conceptual model defined inside another conceptual language,
such as UML.
The GML language defines different entities such as elements,
geometries, and so on, through an object hierarchical structure
as shown in the UML diagram in the Figure 1.
The most part of applies will use only a part of the objects
defined in the Schema at Figure 1. For example if it will have to
model geographic elements, it will have to manage the feature
schema (feature.xsd), if the features will have measurable
properties, it will has to import basicType.xsd o measure.xsd.




Figura 1. GML hierarchical Class

As the reality, which must be represented, becomes more
complicated, more elements will increase the Application
schema.
A typical GML document will be therefore an XML document
consisting of a GML features series: this document is validate
through a GML application schema that defining the data
structure and that is built using and modifying the various
objects defined in the GML Base schema

1.2

The GML base schema

GML base schema, reached to 3.1.0 release, defines several
entities as: geometrical forms, elements, topologies with a
hierarchical structure of chart in figure 1
This base schema gives a simple data whole to represent the
elements and the connection between them. Its possible to take
tools and method also from this schema defining like this new
complex kind of data.
For example, feature schema (feature.xsd) is content in the base
schema. Using the feature.xsd its possible to build GML
feature and featuresCollection, that are the most important
elements of a GML document.


Figure 2 UML diagram of feature schema

1.3

GML Application schema creation

A XML/GML schema describes the structure of a XML/GML
document, which was to convalidated by an apposite diagram to
verify its accordance to the features of the supposed diagram; on
this basis, well have a valid or invalid document.
This Application schema lets the XML/GML document
developers to specify structures and contents of a given
document and to convalidate it at the sometime.
A GML schema was very complex structure and syntax: the
diagram is itself a document written with a GML grammar and
has to conform to the GML basic schema specified rules.
Developing a GML application schema allows the exentinsion
or the limitations of basic types and, according to the field of
application, the GML application schema defines time a time
new types of data.
Definitely the several steps for the scheme building are:

Namespace definition (including the root element)
Distinction parts between of a given basic schema
Addition of element to the basic schema, according to
the own needs

1.4

GML document creation

In GML, the whole of elements composing a map, can be
considered as a group of vectorial informative layer and can be
represented with the feature collection element which contains
information about all the different layer. ________CIPA 2005 XX International Symposium, 26 September 01 October, 2005, Torino, Italy________