Global Positioning System Reference
In-Depth Information
Figure 8.4 Map with the third dimension of time on the vertical axis.
Figure 8.4 shows the information as a 3D graph with time on the vertical axis.
The route on a map is assumed to be on a horizontal plane and time can be
considered to be horizontal planes with the plane of the present shown with
dashed lines. The beginning of the epoch is shown at the origin of the graph and
the progress of the truck shown on the route at different times. Sometime in the
future a geofence is drawn on the route to show where the roadworks will be and
the height extended to form a rectangular box (shown in dashed lines). The event-
processing software would be calculating the probability of the vehicle actually
passing through the box .
This diagram is helped by the fact we are ignoring one spatial dimension (i.e.,
altitude), which is assumed to be constant. Also, the route is constant and the only
changing entities are the truck's positions on the map expressed as north-south or
east-west coordinates on the map (i.e., Northings and Eastings, respectively).
The event engine would have huge numbers of similar boxes defined and
processes that trigger at set intervals to check the boundaries. Trigger rates will
depend on QoS and application requirements. For a fast-moving vehicle a few
minute's delay can represent a significant distance.
Chapter 9 discusses the longer term aspects of mapping that are current in the
research phase: first, the use of the Semantic Web to create an ontology for
Whereness as part of a standardization process, and second, being able to
simultaneously locate position on an existing map, correct it if found to be in
error, or extend it if the measured position is unmapped.
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