The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B6b. Beijing 2008 
volumes, traffic accidents and moving objects) at lane level 
without actually breaking the lane ribbon into pieces or actually 
storing the lane-related events as 2D polygon or 3D feature. 
The conceptual model of lane-oriented 3D dynamic 
segmentation has been designed by the unified modeling 
langrage (UML diagram). As shown in Figure 1, there are three 
parts in the conceptual model, namely cartographic data, linear 
reference system and event. In each part, several objects are 
further defined. 
Figure 1. Conceptual Model of the 3DDS 
• Cartographic representation: a set of 3D lines or 3D 
polygons that can be mapped to a linear datum. 
Cartographic representations provide coordinate 
references as well as the basis for to-scale visualization of 
other components of the linear reference system model. 
• Datum: Set of quantities that may serve as a reference or 
basis for the calculation of other quantities. 
• Network: the topological object, consisting of an 
aggregation of nods and edges that forms the basis for 
operations such as pathfinding and flow. 
• Linear reference method: it provides a means of 
identifying a location by reference to a segment of a 
linear geographic feature and distance from some point 
along that segment. 
• Event: an instant or period in which something happens 
that changes the state of an object. Broadly speaking, 
events include four types: point event, line event, area 
event and moving object such as vehicle. 
Compared with the National Cooperative Highway Research 
Program (NCHRP) model(Adams, Koncz et al., 2001), 3DDS 
has some new characteristics. First, it is datum-oriented instead 
of network-oriented. The multiple geographic representation as 
well as multiple topological representation have been connected 
to datum directly, as such the datum are taken as the core role 
among cartographic representation, network and linear 
reference method. Second, it uses lane ribbon as the minimum 
primitive for geographic representation instead of road 
centerline. Lane ribbon is represented as an elongated region 
with clear boundaries on a road surface, to allow the 
representation of the photorealistic geometric configuration of 
individual lanes. Third, it uses real lane as the minimum 
primitive for network topologic analysis. The costs of routing 
will attached on real lane and each real lane are connected to a 
single lane ribbon for its cartographic representation. Last, it 
uses three dimensional offsets to locate 3D point, line, area and 
volume events. The three dimensional offsets cover horizontal, 
vertical measures relative to geographic position of lane ribbon. 
Shortly, the conceptual model of 3DDS overwhelms the 
traditional one-dimensional dynamic segmentation method in 
its higher accuracy in geovisualization and more flexibility in 
lane-oriented event recording. It facilitates inventory 
management at lane level and wider application in urban 
transportation network systems. 
2.2 Algorithm Flow 
In the conceptual model, the key objects have been illustrated 
and the relationships among the objects have been built. 
However, in order to transfer the conceptual model into 
implementation, a reasonable algorithm flow must be given. In 
the traditional dynamic segmentation method, the algorithm 
flow can be summarized as four steps: constructing route 
system; setting datum; inputting event table; interpolating and 
geovisulizing. As such, an important step is to input sets of lines 
and manually organize linear route system. Basically, the 
traditional algorithm flow will be problematic in microscopic 
urban network because the building of route system is a time- 
consuming task and the work is far more complicated in lane- 
oriented network system. 
In the 3DDS, the algorithm flow has been re-organized as three 
steps, namely event-inputting; datum-setting; dynamic 
segmenting, as shown in Figure 2. 
Figure 2. Flowchart of the 3DDS implementation 
Step 1: Sets of lane ribbons are loaded into virtual geographic 
environments, and those lane ribbons are co-related to lane- 
oriented topologic network, in order to facilitate lane-oriented 
routing and navigation. Two kinds of event tables are input into 
the system. 
Step 2: The datum-setting process in initiated automatically 
when event tables are input into scenes. In this step, the 
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