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grading of large areas, GPS controlled earthmoving equipment, including bulldozers, back-
hoes, road graders, excavators, and compactors, can greatly increase productivity during
the land development process.
Applications of GPS can be divided into two major categories:
1. Location and Tracking: The most common and basic use of GPS is the determination
of a location of a receiver on Earth. The GPS signal is used to determine the “where”
(“locating where it is now”) an object is and is it moving (“tracking”). GPS offers
the location data (latitude, longitude, and elevation) for any receiver point on Earth.
Tracking is the process of monitoring the movement of things. The tracked object
must have a GPS receiver to detect its position information, and the ability to transmit
that data to the tracking station. By processing the GPS broadcast signal, a GPS
receiver determines its location on Earth. By transmitting this location information
to a remote control station (i.e., by wireless radio signal transmission), it enables a
tracking capability at a central control location. As a result, a central control station
can received the reported location information from multiple GPS receivers on a fleet,
and keep track of their locations.
2. Navigation and Geospatial Information System (GIS): GIS is a collection of
computer software and geographic data for processing all forms of geographically
referenced information in a database format. GPS is the “sensor” used to measure and
provide the location data to all this geographically referenced information. In other
words, for any point of interest, the “where” information is provided by GPS. The
“what and how” information is provided by the GIS software system. GIS systems
are widely used in surveying (obtaining a digital terrain map of a section of Earth’s
surface) for road building, mining, and farming applications. Apart from locating
a point on the planet, GPS signal processing tools also provide information as to
how to travel from one location to some other location on the planet. GPS provides
navigation information for ships and planes. Given a desired destination, if the current
position of an object can be determined via GPS, then a motion path can be planned.
This planned path can be update in real-time as the object moves closer to the desired
destination. Obstacles along the way or other constraints can be imposed to modify
the planned path.

6.13.1 Operating Principles of GPS
GPS employs about 24 satellites in 20 000 km circular orbits [12]. These satellites are
placed in six orbit planes with four operational satellites in each plane. The satellites orbit
the Earth every 11 hours and 58 minutes. A GPS receiver receives the GPS broadcast signal
and and uses the “trilateration” method to calculate the receiver’s location. A GPS receiver
must be locked on to signals from at least three satellites to determine its location (latitude,
longitude, and altitude). Using a fourth satellite signal allows the GPS receiver to determine
its position more accurately. Due to the synchronization error between the receiver clock
and the atomic clocks on the GPS satellites, the signal from the fourth satellite will not
intersect at an exact point in the trilateration. Then, the GPS receiver firmware searches
for a single correction that can be applied to all four satellite signals that would make the
trilateration algorithm work.
The basic setup of the GPS receiver is shown in Figure 6.71. The signals transmitted
from the satellites are received by the antenna. This signal is then filtered and amplified
using a signal conditioning unit. The conditioned signal is later digitized by an ADC
(analog-digital converter). This digitized signal is then sent to the software block for post
processing. The user position (the GPS receiver position) obtained can be presented in terms