Global Positioning System Reference
In-Depth Information
periments. This is called a top-down deductive method. In simulations,
this method is comparable to an object's implementation of a mathemat-
ical model. On the other hand, experimental scientists use a bottom-up
inductive method to derive a law. After dropping all kinds of objects from
different heights and determining the duration of the fall, the scientist can
create a table of masses and durations and look for a formula to predict
every value in the table.
In order to keep the vision simple and avoid complex mathematics,
the model of a car is more intuitive than the gravity example. Look-
ing at the
Car
object, introduced on page 9, an initial implementation re-
quires only a
position
and some rules for motion, for example,
accelerate
(increase speed),
break
(slow down and stop), and
steer
(change direction).
These rules can be validated using a map (a rectangle moving on a line).
Then, the next implementation step might be a simple navigation system
(see page 103) to guide the car to a destination.
The experimental approach requires real-world data of a car. A
GPS
trace
(see page 39) can be used to validate the simulation of a car. The
acceleration values imply mass and force (engine power), and the track's
positions imply a street that should be represented on a map (see page 79).
By combining simulated cars and traced real cars in one scenario, one
can validate the map and the behavior of each of the car types. Step-by-
step, the scenario and each of the participating cars becomes more realistic.
Think of a (city) scenario for busses and another one for subways, which
can be projected on a city map as two separate layers. The server provides
date and time for each scenario, and the user (observer) can see how a bus
and a subway meet at the same station.
Many servers, as different aspects of the same world, could be combined
to create one reality! As long as they are reflecting the real world, they
should allow projections (layering) of any real-world, real-time information
into the simulation.
2.4
Real-World Objects (ROs)
In Java, everything is built on top of the
Object
class to manage the com-
munication of the Java program with the external platform and network
via JVM. To build real-world simulations, it would be nice to have a toolkit
containing basic classes representing real-world objects. Classes of
Car
s, for
example, would be useful for simulating trac. Or, a programmer could
extend
a
Car
class to simulate varying set-ups for races.
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