International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
Non-spatial information is introduced into the system as road
event. The road event includes all non-spatial information
including attributes, time of occurrence, state and physical
components of the road. Examples of typical road events are:
traffic accident, construction project, road facility, video image,
pavement type and road type. Road Events are assigned to
geometry. The thematic road data has no spatial character
including the third-dimension. The geometrical properties of the
road data is provided by referencing the geometry component of
the model fully in third dimension. The ‘Road Event’ object
stores all non-spatial information according to the provided road
event identifiers in the event catalogue. Having agreed on the
standards for identification, associations between road events
and geometrical elements were made. There was a 0.1: 0..*
relationship between the Geometry (‘Point Geometry’, ‘Linear
Geometry’ and ‘Area Geometry’) and Road Event objects.
Every ‘Road Event’ should be assigned to one of the geometry
types and many road events may be assigned to one geometrical
object. All non-spatial properties of Road Event were stored in
the object ‘Road Event Properties’. This object has a tree
structure with which it is possible to expand properties of road
events to any desired level. Every road event may have many
road event properties and every road event property must be
assigned to only one road event, where 1:0..1 association was
used for describing this. With the objects introduced above, the
requirements of road administrations were fulfilled in multi
dimensional space, including planar and vertical sections.
In order to integrate 1-D, 2-D and 3-D coordinates, the member
method Dynamic Reference Transformation of the ‘Road Event’
object was introduced. As all linear reference systems are based
on the specification of the direction and distance from a known
point to an unknown point, every linear reference system can be
defined using the (/, q) system, where (/) is the distance along
the road between the origin and the start point of the road event,
and (g) the distance normal to the linear element at the start
point of the road event, called linear element system. The linear
element system is a planar system (2-D), where (/) coordinates
are identical with the projection of road alignment in (, y)
plane. Since road administrations consider the use of linearly
referenced methods to be inevitable, the transformation from (x,
y, 2) to (I, q) systems was modeled. During this transformation,
linearly referenced data was not stored in 1-D, but rather in 3-D.
The transformation needs to be realized dynamically, in order to
prevent data inconsistencies and redundancy. The geometrical
properties of a road axis in the (x, y) plane are described using
the linear elements in 3-D and the usage of a three-step
transformation (Gielsdorf, 1998) was adapted for the
requirements of road administrations (Demirel, 2002).
The metadata component includes integrity constraints, history
and quality. In GIS, due to redundancy, integrity constraints are
required wherever geometry interacts. Several additional
integrity constraints are defined externally in order to validate
geometry and topology. The history for all objects and
relationships is stored in the ‘History’ object, adopting the
transaction log approach. One event type can have many history
objects, for instance an operator can update many objects at one
time (before the transaction), and every history object is
associated with only one event type. All these processes arc
controlled by transaction rules. By using the history object, it is
possible to report or re-create a required transaction and to
model the current, past and future situations. Using the defined
history objects, the time component is covered by the designed
conceptual data model (Demirel, 2004). The quality aspect is
implemented using member methods of the individual objects.
The history approach is not followed, since it is very unlikely
that errors or poor quality data needs to be regenerated. Using
this approach the quality of the current data is reproducible at
any time in the form of documents or tables. During the
proposed data model, the quality control, error trapping, data
consistency checks and acceptance tests are designed which will
definitely increase acceptance and the success level of the
system. The generic data model was described using the Unified
Modelling Language (UML), where relationships are classified
as dependency, association, generalization and realization
(Booch et al., 1999) and illustrated in Figure 2.
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In order to increase the efficiency and highlight the benefits of
GIS-T, this study considered a progressive approach appropriate
to the conceptual data modeling requirements of an entire
highway agency. The main features of the proposed conceptual
data model can be summarized as follows:
= Topology, geometry and thematic information is
conceptually independent
= Multiple topologic representations, supporting
different abstraction levels, are realized with two
abstraction levels of topology, in order support
diverse applications in highway agencies.
= With the incorporation of height information and the
designed objects in the conceptual data model, non-
planar topological model is achieved. In order to
achieve non-planar topology, other techniques were
also proposed including, introducing constraints by
means of adjustment techniques.
" Road information, such as data collected through
linear referencing systems or cross-sectional design
information, is modeled with decomposition of spatial
ànd non-spatial characteristics.
= Highway business-rules are modeled using integrity
constraints, user defined methods and triggers.
= Existing road information was be integrated into the
system without redundancy through defined methods
and adjustment techniques.
= Metadata, including history information was modeled.
Quality specifications, including accuracy
certification, were defined in the conceptual data
model for objects and introduced methods.
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