Objects in Motion - Programming GPS and OpenStreetMap Applications with Java - page 70

of the ROAF Turing Test is to obscure these different modes to external
observers.
To get a grip on the relationship (aggregation) of the RealObject to its
GPSunit , a designer can describe a use case:

1. Imagine you (a body with location, mass, and size) represent the
RealObject carrying a cell phone (a reference for other people to reach
you and inquire information) and a GPSunit (hidden in your jacket).

2. You are standing on or near a bank of a river (location) and you
turn on the GPS device, which is attached to you and retrieves your
geographical Position and the universal time ( GPSinfo ).

3. A friend calls you and ask, \Where are you?" You answer, \I'm
at Regen street parallel to the Regen river" (local knowledge). To
be more precise, you look at the GPS and say, \I'm at N49.031,
E12.103 ." He asks, \What time is it?" You read it on the GPS, the
most precise clock available and reply, \Let's meet downtown at the
cathedral."

4. You begin to walk downtown to meet your friend. The GPSunit
refreshes your position approximately every second and logs every
GPSinfo(lat,lon,elev,time) to its internal memory.

5. You're late and jump into a cab. The GPS is now logging the cab's
trace along the streets.

The design process can simply follow this use case:
The constructor

RealObject( GPSinfo gpsInfo )
{

gpsUnit = new GPSunit( gpsInfo );

}

sets place and time (of birth). The Position of the RealObject can not be
set externally|you can not move a body by supplying coordinates like in
Star Trek. Similarly, people usually guide each other by names of streets or
places. The GPSunit records the RO coordinates, while the RO can describe
its motion in terms of phrases like \turn left at the next intersection (where
you can see the cathedral), and then walk straight in the direction of the
cathedral."
Whenever exact position or time are needed, read it from the GPSunit :

final public GPSinfo getGPSinfo() // where am I and whats the time?
{

return gpsUnit.getGPSinfo(); // ask my internal GPS

}