yl CAN
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
4. Implementation of the Generic Data Model
In order to test the developed concepts, two different datasets
were used, being the 1:10.000 scaled data set of Brandenburg
State Office for Traffic and Roads (BLVS), Germany and
1:25.000 scaled data set from western Turkey. Within pilot
projects, the first abstraction level topology, geometry and
thematic components were implemented. The developed
approaches were successfully implemented using SQL scripts
directly into Oracle8i, after the physical design of the
conceptual data model. First, abstraction level topology,
geometry and thematic components were implemented. Two
different GIS software were used, GeoMedia Professional 3.0
and ArcInfo8™,
In GeoMedia Professional 3.0, the conceptual data model’s
thematic and geometry components were implemented. Two
methods, the Detecting Alignment Elements and Dynamic
Reference Transformation, were successfully implemented.
Within the proposed conceptual data model, it was assumed that
linear elements are defined by means of their parameters and
then generated without storage of any other geometrical
information. However, although it was possible to parameterize
defined geometric elements and introduce them to the system;
* It was not possible to generate these geometrical
clements automatically using their parameters,
without the storage of any other geometrical
information. Because, geometrical features must be
identified by their planar coordinates.
« It was not possible to visualize the clothoid.
The first mentioned problem was solved by implementing the
geometrical elements redundantly and controlling the
redundancy with the developed methods. The second problem,
the visualization of clothoid, was solved with the help of other
geometrical elements, since it was not possible to define
geometrical objects in the system.
The topology component can not be implemented in the manner
proposed in the conceptual data model. The main problem
encountered was the lack of user-defined types. meaning
implementation opportunities were limited due to software
vendor defined features, specifically spatial features. Topology
information is considered differently in GeoMedia. Only in the
“Maintain Coincidence Mode” ("On-the-Fly" topology
instruction), displacement of one point has the consequence
that, points which are situated within a determined distance will
follow this movement. Additionally, it is not considered
whether these points are assigned to topological nodes or not.
There are some additional reasons, which affect the
implementation of topology. The available mechanisms were
insufficient in controlling the redundancies. The versioning
concept is unavailable. A transaction is always automatically
terminated in the system after a new object is created. This
requires consistency checks to be realized immediately.
However, in the conceptual data model consistency checks are
pre-required for some entries, such as ‘Link’ and ‘Node’. There
are also situations where this is reversed, such as determining
‘Point Geometry’ and ‘Node’ relations. In this case control
mechanisms did not provide expected results. Additionally, it is
not certain whether the quantity of the consistency conditions
required is realizable using triggers. A further problem results
from the fact that the user does not have influence on the end of
a transaction
Using the second selected software Arcinfo8'M, users can
define feature types and are not limited to the software vendor's
concepts and definitions due to provided ArcObject concept.
With the *geometry network" possibility, topological elements
can be implemented according to the descriptions in the
conceptual data model. In ArcInfo8TM integrity constraints
called “validation rules” can be defined by the user.
Additionally, the versioning concept is available. The
conceptual data model was successfully implemented through
ArcInfo8™, although during the implementation some
problems needed to be solved. These are as follows;
l. Geometrical elements can not be generated using
their parameters.
The main concept is similar to that used by GeoMedia
Professional, where geometrical features are assigned
to their planar coordinates for visualization purposes.
In order to solve this issue, geometrical features and
parameters were stored by using the user-defined
objects and methods. The occurred redundancies were
controlled using user-defined methods and validation
rules.
2. Features having geometrical characteristics must be
assigned 1o a pre-defined geometrical Jeature of
ArcInfo8"".
Regardless whether an object is defined as a
geometrical component or not, every object which
should be visualized in GIS must have planar
coordinates assigned to it, including the topological
elements: node and link. During the implementation,
an additional column was added to the physical data
model table in order to define the geometry of feature.
Consequently, objects such as linear clements were
stored redundantly in the shape column with their
geometrical information, in this case the coordinates
of the polygon's points. These redundancies were
controlled by consistency rules.
3. The linear element clothoid is not supported in
ArciInfog
Although clothoids were stored with their parameters
in the database, automatic generation of
parameterized elements was not possible. During
visualization clothoids were simplified as line and arc
objects.
4. By using the "geometric network" of ArcInfo8!",
topological relations can only be modeled between
geometrical objects.
With the “geometric network" of ArcInfo8™,
topological objects and relationships between each
other could be established. However, due to non-
separation between geometry and topology, this
establishment can only be made between geometrical
objects. Due to this limitation, implementation of a
0..1:1 relationship between ‘Node’ and ‘Point’ could
not be realized.
In order to implement the proposed conceptual model,
modifications were made with respect to fourth item. The
geometric element point was subdivided into three parts being;
node, element point and intermediate point. ‘Node’ was
preserved as node. From the other new defined objects ‘Element
Point" defines the beginning or ending point of a linear element.
The ‘Intermediate Point” was introduced in order to indicate any
location along a link, which is neither the beginning nor the
ending point of the linear element. Additionally consistency
i315
