| Using the Data |
In the last couple of sections, we saw that the most essential
function of a GPS receiver is to pick up the transmissions of at
least four satellites and combine the information in those transmissions
with information in an electronic almanac, all in order to figure
out the receiver's position on Earth.
Once the receiver makes this calculation, it can tell you the latitude,
longitude and altitude (or some similar measurement) of its current
position. To make the navigation more user-friendly, most receivers
plug this raw data into map files stored in memory.
You can use maps stored in the receiver's memory, connect the receiver
to a computer that can hold more detailed maps in its memory, or
simply buy a detailed map of your area and find your way using the
receiver's latitude and longitude readouts. Some receivers let you
download detailed maps into memory or supply detailed maps with
plug-in map cartridges.
A standard GPS receiver will not only place you on a map at any
particular location, but will also trace your path across a map
as you move. If you leave your receiver on, it can stay in constant
communication with GPS satellites to see how your location is changing.
With this information and its built-in clock, the receiver can give
you several pieces of valuable information:
- How far you've traveled (odometer)
- How long you've been traveling
- Your current speed (speedometer)
- Your average speed
A "bread crumb" trail showing you exactly where you have
traveled on the map
The estimated time of arrival at your destination if you maintain
your current speed
To obtain this last piece of information, you would have to have
given the receiver the coordinates of your destination, which brings
us to another GPS receiver capability: inputting location data.
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