Data Hacking

166 Part III — Data Hacking
Put simply, this means you can move around longer with a Garmin Vista than you can with a
basic eTrex without overwriting existing data.
Let’s take a look at the different types of information your GPS collects and stores.
Position, Velocity, Time
Position, Velocity, Time (PVT) data is at the core of GPS. These three data categories cover
where you are, what time it is, and how fast you are moving in relation to your last known position.
This information is what GPS is pretty much all about. Let’s take a look at the three parts
of this data.
Position
Position data is information about where on the Earth’s surface the GPS actually is. You can
think of this as a spot reading taken at a point in time.
Position information consists of two parts:
Latitude: These are lines that form concentric circles around the globe. The equator is
the longest line of latitude, and they shrink in size until they become a point at the north
and south poles (see Figure 8-1). They are measured in degrees. The equator is 0°, the
north pole is +90° and the south pole is -90°.
Longitude: Lines of longitude extend from the poles (see Figure 8-2). There are 360° in
a full circle, but longitude is measured 0° to 180° east and 0° to 180° west, with 0° passing
through Greenwich in London and 180° passing through the Pacific Ocean.
W
N
Equator
FIGURE 8-1: Lines of latitude
S
E