Data Hacking

170 Part III — Data Hacking
y
N
x
FIGURE 8-6: Direction of travel
calculated by comparing the last
location to the current location
However, some newer, more expensive receivers contain an electronic compass that works just
like any other compass, detecting the Earth’s magnetic field. This information can be combined
with the data from the GPS satellites to provide you with even greater accuracy in plotting your
direction of travel (see Figure 8-7).
FIGURE 8-7: Electronic
compass in action
The lack of a compass is why some GPS receivers, depending on type, can’t actually tell you which
way to go to get to a certain point unless you are moving. Without a compass, it can’t determine
the receiver’s direction from only the GPS satellite signal.
This can be a real problem at times, and the pointer on some receivers will spin wildly when the
unit is stationary. An electronic compass eliminates this behavior (see Figure 8-8).
Remember, however, that built-in digital compasses are subject to the same problems as standard
compasses (such as being affected by close proximity to metal and other magnets).
Time
Thanks to the four atomic clocks on board each GPS satellite, you can be pretty confident of
getting a good time signal from the satellites. Local time zone information can be inputted into
the GPS (see Figure 8-8) along with daylight saving information (see Figure 8-9).