Electronic Navigations: GPS,GPS terms, GPS use and using Waypoints

1. Noakhali Science and Technology University
Course Tittle
Seamanship and Maritime navigation
Course Code
OCN4107
Assignment on:03
Electronic Navigations: GPS,GPS terms, GPS use and using Waypoints
Submit To
Razat Shovro Dash
Lecturer,Dept.of Oceanography
NSTU
Submit By
Azad Uddion Sojib
Enroll:ASH1718010M
Submission Date:21/08/2020

2. Table of contents
Serial
Number
Archives of Title Page
Number
01 What is Global Positioning System (GPS) 01
02 Segments of Global Positioning System (GPS) 01-05
03 GPS Signal 05
04 How it (GPS) work 06
05 How accurate is GPS 07
06 Uses of GPS 07
07 Drawbacks of GPS 08
08 Applications of GPS system 08-09
09 pivotal Terms of GPS 09-10
10 Using Waypoints 11-13

3. Global Positioning System (GPS):
Global Positioning System or GPS, is a technology that can give your accurate position
anywhere on earth (latitude/longitude). It can be defined as “a satellite-based navigation
system which records and displays location of an object on earth (in terms of
coordinates, i.e. latitude and longitude) as well as height of a place above mean sea
level.
A GPS device receives signals from satellites and these signal codes are processed &
converted into values showing position, time and velocity (what we see on screen of
GPS device). The instrument to which we generally call „GPS‟ is basically a GPS
receiver and it is a small part of a large system.
A complete Global Positioning System consists of following three segments;
1. space segment,
2. control segment
3. user segment.
Space segment:
Space segment consists of dedicated satellites for Global Positioning System and are
referred as space vehicles (SVs). There are twenty-four satellites in a nominal GPS
constellation. Out of these twenty-four satellites three are spare satellites which start
operating if some of the functional twenty-one satellites have some operational problem.
These satellites remain in six orbital planes (four in each) and are positioned such that
five to eight of these SVs visible from any place on the earth at a given point of time.
Control segment:
The control segment consists of tracking stations located around all over world. There
are master control station and monitoring stations in control segment.
The Control Segment consists of 3 entities:
A. Master Control Station
B. Monitor Stations

4. C. Ground Antennas
A. Master Control Station
• The master control station, located at Falcon Air Force Base in Colorado Springs,
Colorado, is responsible for overall management of the remote monitoring and
transmission sites.
• Provide commands and control of the GPS constellation.
• It generates and uploads navigation messages and ensures the health and
accuracy of the satellite constellation.
• It receives navigation information from the monitor stations, utilizes this
information to compute the precise locations of the GPS satellites in space, and
then uploads this data to the satellites.
B. Monitor Stations:
• Monitor stations track the GPS satellites as they pass overhead and channel
their observations back to the master control station.
• Monitor stations collect atmospheric data, range/carrier measurements, and
navigation signals.
• The sites utilize sophisticated GPS receivers and are operated by the MCS.
• There are 16 monitoring stations located throughout the world, including six from
the Air Force and 10 from the National Geospatial-Intelligence Agency (NGA).
C. Ground Antennas:
• Ground antennas monitor and track the satellites from horizon to horizon.
• They also transmit correction information to individual satellites.
User segment:
User segment of GPS is what we use i.e. GPS receiver. It also includes the GPS user
community. A GPS receiver consists of a screen for displaying information, buttons to
operate it and antenna to receive signals from satellites. The antenna may be in-built in
receiver instrument or it may be externally attached to it. Signals from minimum four
satellites are required for a GPS receiver to compute location (x, y & z) and time (t).
GPS receivers are essential part of navigation system of air crafts and ships.
The User Segment comprises of anyone using a GPS receiver to receive the GPS
signal and determine their position and/or time. Typical applications within the user
segment are land navigation for hikers, vehicle location, surveying, marine navigation,
aerial navigation, machine control etc.

5. Function of Space Segment
➢ The Space Segment is designed to consist of satellites orbiting the earth at
approximately 20200 km every 12 hours.
➢ Each GPS satellite has several very accurate atomic clocks on board. The clocks
operate at a fundamental frequency of 10.23MHz. This is used to generate the
signals that are broadcast from the satellite.
➢ The satellites broadcast two carrier waves constantly.
A. L1 carrier: L1 carrier has two codes modulated upon it.
i. The C/A Code or Coarse/Acquisition Code is modulated, has a
length of one millisecond; its chipping rate is 1.023MHz with
corresponding wavelength of 300 mts.
ii. P-code or Precision Code: Has the frequency of 10. 23MHz.this
refers to the sequence of 10.23 million binary digits or chips per
second. Frequency also referred as the chipping rate of p-code. P-
code is extremely long and repeats only after 266 days. Portion of
seven days each are assigned to the various satellites. As a
consequence, all satellite can transmit on the same frequency and
can be identified by their unique one-week segment. This technique
also called as the Code Division Multiple Access (CDMA)
B. L2 carrier: has just one code modulated upon it. The L2 P-code.
Broad cast messages: for precise geodetic applications, third type of
signal transmitted from the GPS satellite is broad message sent at a
rather slow rate of 50 bits per sec and repeated every 30 sec. chip
sequence of p-code and C/A code are separately combined with the
stream of messages bit by binary addition i.e. same value for code
gives 0 and different value gives 1.

6. Figure: Space Segment
Function of Control Segment
❖ The Control Segment consists of one master control station, 5 monitor stations
and 4 ground antennas distributed amongst 5 locations roughly on the earth's
equator.
❖ The Control Segment tracks the GPS satellites, updates their orbiting position
and calibrates and synchronizes their clocks.
❖ A further important function is to determine the orbit of each satellite and predict
it’s path for the following 24 hours. This information is uploaded to each satellite
and subsequently broadcast from it. This enables the GPS receiver to know
where each satellite can be expected to be found.
The most important tasks of the control segment are:
Observing the movement of the satellites and computing orbital data (ephemeris)
Monitoring the satellite clock sand predicting their behavior
Synchronizing on board satellite time
Relaying precise orbital data received from satellites in communication
Relaying the approximate orbital data of all satellites (almanac)
Relaying further information, including satellite health, clock errors etc.
INFORMATION IN A GPS SIGNAL
The GPS signal contains mainly two types of data, they are:
I. Ephemeris data
II. Almanac data

7. Ephemeris data is constantly transmitted by each satellite and contains
important information such as status of the satellite (healthy or unhealthy),
current date, and time. This part of the signal is essential to determining a
position.
Almanac data tells the GPS receiver where each GPS satellite should be at any
time throughout the day. Each satellite transmits almanac data showing the
orbital information of that satellite.
How GPS works:
➢ GPS satellites circle the earth twice a day in a very precise orbit and transmit
signal information to earth.
➢ GPS receivers take this information and use triangulation to calculate the user's
exact location.
➢ the GPS receiver compares the time a signal was transmitted by a satellite with
the time it was received. The time difference tells the GPS receiver how far away
the satellite is.
➢ the receiver can determine the user's position and display it on the unit's
electronic map.
➢ A GPS receiver must be locked on to the signal of at least three satellites to
calculate a 2D position and track movement
➢ four or more satellites in view, the receiver can determine the user's 3D position

8. How accurate is GPS?
➢ GPS receivers are extremely accurate due to parallel multi-channel design.
➢ Garmin's 12 parallel channel receivers are quick to lock onto satellites when first
turned on and they maintain strong locks, even in dense foliage or urban settings
with tall buildings.
➢ Certain atmospheric factors and other sources of error can affect the accuracy of
GPS receivers.
➢ GPS receivers are accurate to within 15 meters on average.
➢ GPS receivers with WAAS capability can improve accuracy to less than three
meters on average.
➢ Users can also get better accuracy with Differential GPS (DGPS), which corrects
GPS signals to within an average of three to five meters.
Advantages/uses of GPS
Reliable to much extent
Unlimited Users Capacity
Operates in all Weather conditions
Complete coverage of Globe
Updated regularly
Free of cost and Easy to use
Compact-Mobile phones/Watches
Full time access
Determination of exact location, distance & speed.
Gives you inf. About Latitude & Longitude.
Allows to search for nearby Amenities. Determination of traffic, weather
conditions.
Keep track of your friend’s or target’s location.
GPS is extremely easy to navigate as it tells you to the direction for each
turn you take or you have to take to reach to your destination.
GPS works in all-weather so you need not to worry of the climate as in
other navigating devices.
The GPS costs you very low in comparison other navigation systems.
The most attractive feature of this system is its100% coverage on the
planet.
It also helps you to search the nearby restaurants, hotels and gas stations
and is very useful for a new place.
Due to its low cost, it is very easy to integrate into other technologies like
cell phone.
The system is updated regularly by the US government and hence is very
advance.
This is the best navigating system in water as in larger water bodies we
are often misled due to lack of proper directions.

9. Disadvantages/drawbacks of Global Positioning System
➢ Sometimes the GPS may fail due to certain reasons and in that case, you need
to carry a backup map and directions.
➢ These systems rely on batteries. Once the battery is drained out, the system
does not work.
➢ Sometimes the GPS signals are not accurate due to some obstacles to the
signals such as buildings, trees and sometimes by extreme atmospheric
conditions such as geomagnetic storms.
➢ Price of the system is a major concern. GPS systems cost a high amount if they
have lots of features. Accuracy is again an issue.
➢ The systems are not always updated, so we do not know when a road has been
closed or when a new road has been opened
Applications of GPS system
Tracking is useful because it enables a central point to monitor the position of
several vehicles or people, in real time, without them needing to relay that
information explicitly. This can include children, criminals, police and emergency
vehicles or military applications. GPS vehicle tracking is also used to locate
stolen cars, or stolen mobiles.
location
o Once we know our location, we can, of course, find out where we are on a
map, and GPS mapping and navigation is perhaps the most well-known of
all the applications of GPS.
tracking application
o A tracking application are not that much popular as the navigation
applications. But so many people take uses of them. It enables users to
find a location of any object that is tagged with a system.
Navigation applications
o are the most famous GPS applications. The latest releases of those
applications allow users to have much advanced features and facilities.
ROAD APPLICATIONS
o Used to determine location, speed, traffic and distance to destination.
o Used to search nearby Amenities like malls, restaurants, theatres etc.
o Sources include-Mobiles, Laptops, GPS mount for automobiles.
SPACE APPLICATIONS
o Weather monitoring, Launch Vehicle tracking, Disaster Alerts, Space
Shuttle nav.
o Keep track of other space elements like space debris, asteroids, etc.
RAIL APPLICATIONS
o To maintain smooth flow of traffic.
o Prevent collisions by precise knowledge of other trains locations.

10. MILITARY:
o GPS systems are installed with fighters, bombers, tankers, helicopters,
ships, submarines, tanks, jeeps and soldiers to combat various attacks.
AVIATION APPLICATIONS:
o GPS provides position determination for all phases of flight from
departure, and arrival, to airport surface navigation.
AGRICULTURE:
o farm planning, field mapping, soil sampling, tractor guidance, crop
scouting, variable rate applications, and yield mapping.
AUTOMOBILE
o Car Navigation
o Dynamic Vehicle Routing
o Tracking Rental Cars
o Monitoring High Risk Auto Loans
o Hand held, Tracking, GIS, Survey,
o Manufacturing.
Common Pivotal Terms of GPS
Accuracy – A measure of how close an estimate of a GPS position is to the true
location.
Bearing – The compass direction from a position to a destination, (also called an
azimuth). In a GPS receiver, bearing usually refers to the direction to a waypoint.
Coordinate Systems – Such as latitude/longitude, represent your position on the earth
to a flat surface like a sale map.
Course – The compass direction you are trying to follow from your starting point to the
point you are trying to reach.
Declination Setting - GPS units can be adjusted to the amount of magnetic declination
in the area of use.
Differential GPS (DGPS) - An extension of the GPS system that uses land-based radio
beacons to transmit position corrections to GPS receivers. DGPS reduces the effect of
selective availability, propagation delay, etc. and can improve position accuracy to
better than 10 meters.
Direction – The direction between two locations is usually called a bearing, azimuth, or
course.
Error – Measurement of horizontal position error in feet or meters based on a variety of
factors including Dilution of Precision (DOP) and satellite signal quality.

11. GOTO – The selected point you wish to travel to or find. It may be a position fix or part
of a route or track.
Heading - The direction in which you or your vehicle are moving. For boat or airplane
operations, this may differ from actual Course Over Ground (COG) due to winds,
currents, etc.
Latitude - A position's distance north or south of the equator, measured by degrees
from zero to 90. One minute of latitude equals one nautical mile.
Location – The actual physical place you occupy. The difference between a position fix
and location is that a location is where you really are and a position fix is where a GPS
unit says you are.
Longitude - The distance east or west of the prime meridian (measured in degrees).
The prime meridian runs from the North Pole to the South Pole, through Greenwich,
England.
Magnetic Declination – The difference between true north and magnetic north at a
specific location. Navigation - The act of determining the course or heading of
movement. This movement could be for a plane, ship, automobile, person on foot, or
any other similar means.
NAVSTAR - The official U.S. Government name given to the GPS satellite system.
NAVSTAR is an acronym for Navigation Satellite Timing and Ranging. Position fix - The
GPS receiver's computed position coordinates.
Precision – Measure of the “repeatability” of the data. Taking repeated readings from a
point will improve the precision of the sample mean.
Route - A group of waypoints entered into the GPS receiver in the sequence you desire
to navigate them.
Track - Your current direction of travel relative to a ground position (same as Course
Over Ground).
Wide Area Augmentation System (WAAS)
A system of satellites and ground stations operated by the Federal Aviation Authority
that provide GPS signal corrections for better position accuracy for airplanes. WAAS
consists of approximately 25 ground reference stations positioned across the United
States that monitor GPS satellite data. Two master stations, located on either coast,
collect data from the reference stations and create a GPS correction message. A
WAAS-capable receiver can be adapted to ground use and give you a position accuracy
of better than three meters, 95 percent of the time

12. Waypoint/Landmark:
Waypoints are locations or landmarks worth recording and storing in your GPS. These
are locations you may later want to return to or avoid. They may be check points on a
route or significant ground features such as a campsite, the truck, a cultural resource, or
a favorite fishing spot). Waypoints may be defined and stored in the unit manually by
taking coordinates for the waypoint from a map or other reference. This can be done
before ever leaving home. Or more usually, waypoints may be entered directly by taking
a reading with the unit at the location itself, giving it a name, and then saving the point.

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