Global Positioning Systems
INTRODUCTION
Agriculture and Engineering are changing
industries. New technologies have made it
possible to increases the accuracy of certain
tasks. The goal of the Global Positioning
Systems unit is to introduce precision
agriculture and engineering into the
curriculum.
General instruction of Global Positioning
Systems will be presented, as well as
technical information and technical
applications using the Garmin Dakota 20
handheld units. It is our hope that this
curriculum will give both instructors and
students a comprehensive understanding of
Global Positioning Systems, applicable to a
wide variety of careers.
I – What is GPS
1 – Global Positioning Systems – a
network of satellites that makes it
possible to precisely identify a location
on earth
2 – U.S. Dept. of Defense satellites
transmit signals while orbiting the Earth
in a precise pattern
3 – System comprised of:
a - at least 24 satellites
• 1 – in a distinct pattern
• 2 – approximately 12,000 miles above the
earth
• 3 – contain atomic clocks accurate to 1 second
of error every 1 million years
b - ground control stations
• 1 – uplinks corrected orbital and clock
information
• 2 – 5 stations worldwide
c – receivers
• 1 – handheld GPS receivers
• 2 – mounted on farm implements, vehicles,
planes, boats, ect
II – How does GPS work
1 – Each satellite sends a data message
to the receiver including
a – satellite location
b – clock corrections
c – rough information about other satellites
in the constellation
2 – The time it takes the signal to reach
the receiver allows the receiver to
calculate the distance to the satellite
For example: You are lost
and someone tells you
that you are 625 miles
from Boise, Idaho.
You ask someone else
where you are and they
tell you that you are 690
miles from Minneapolis.
You could be at one of
two points where the
circles intersect.
You ask a third person
and they tell you that you
are 615 miles from
Tucson, Arizona.
Which means that you
are in Denver, Colorado
according to where the
circles intersect.
3 – Using 3 satellites, latitude and
longitude can be identified
4 – Altitude can be identified with a
fourth satellite
5 – Differential GPS (DGPS) – uses
known beacon locations to correct
satellite within inches
III – History
1 – The U.S. Dept. of Defense (DOD)
designed and implemented the system
for military applications
2 – This system was referred to as
NAVSTAR, or the Navigation Satellite
Timing and Ranging by the DOD
3 – The first satellite was launched in
1978
4 – A full constellation of 24 satellites
was completed in 1994
5 – GPS was to become available to
civilians by an executive decree in the
1980’s and in May 1, 2000 GPS became
fully available when the Selective
Availability, or intentional clock noise,
was turned off
IV – Uses and Careers
1 – Engineering
a – city planning
b – city information systems
c – construction site restoration
2 – Military
a – troop deployment
b – navigation
c – artillery fire
3 – Outdoor Recreation
a – hiking and camping
b – marking and finding specific recreation
location
4 – Automotive/Aviation
a – navigate to specific location
b – identify location if lost, stolen, or in
need of repair
c – locate and track fleet vehicles
5 – Agriculture
a – Precision Agriculture – management of
the farming operation in order to maximize
production and profitability
• 1 – Includes cropping systems, livestock
production, waste management, the protection
of the environment and the enhancement of
biological diversity (PAIT, Iowa State University).
• 2 - The goal is to increase the efficiency of the
farming system by making site-specific
decisions rather then a whole system need
b – Field Guidance
• 1 – reduce skips and overlap
• 2 – mark locations
– a – insect and weed infestations
– b – low yield
– c – soil characteristics
• 3 – create and follow accurate rows
• 4 – advantages over foam
– a – drive 20% faster with light bar in cab than foam
30 feet away
– b – can be used at night
– c – foams can freeze
• 5 – custom application of specific locations
• 6 – variable rate application of fertilizers and
seed
c – Field Information Management
• 1 – measure acreage accurately
• 2 – keep records
– a – yield
– b – application rates
– c – infestations
• 3 – map fields for drainage
• 4 – create topographical maps for variable rate
application
V – Terminology
1 – Atomic Clock - very precise clock
that uses elements cesium or rubidium
with error of one second per million
years; GPS satellites contain multiple
atomic clocks
2 – Beacon – Land based transmitter
that emits signals in all directions,
broadcasting correction data to nearby
GPS receivers for greater accuracy
3 – Differential GPS (DGPS) - GPS
system that uses beacons to correct
GPS receivers; DGPS reduces the effect
of selective availability, weather,
buildings, etc. and can improve position
accuracy to within feet
4 – Waypoints - Locations or landmarks
worth recording and storing in your GPS
5 – Bearing - The compass direction to
a waypoint measured to the nearest
degree
6 – Course - Your actual current
direction of travel (Course Over Ground
or Track)
7 – Heading – Direction of travel
relative to the 3600 of a compass
8 – Prime Meridian – A reference line
from which longitude is measured, run
between poles and passes through
Greenwich, England; divides the east
and west hemisphere
9 – Equator – A reference line from
which latitude is measured; divides the
north and south hemispheres
10 – Latitude - Position north/south of
the equator measured by degrees from
zero to 90
11 – Longitude - The distance east or
west of the prime meridian
12 – Coordinate - A set of latitude and
longitude numbers that describes your
location on or above the earth
A – Divided into hours, minutes, seconds
and fractions thereof
• 1 – Latitude
– One hour = 60 degrees
– One degree = 60 minutes
– One minute = 60 seconds
• 2 – Longitude
– One hour averages 15 degrees as longitudinal lines
get narrower toward the poles (24 hour day/360
degrees)
B – One minute = one nautical mile
13 – Statute Mile – Equal to 5,280 feet
or 1,760 yards (1,609 meters)
14 – Nautical Mile - Used in sea and air
navigation and based on the length of
one minute of latitude/longitude; equal
to 1,852 meters (about 6,076 feet)
15 – Triangulation - Method of
determining the location of an unknown
point by using bearings from two
known points
16 – Geographic Information Systems
(GIS) - system or software capable of
assembling, storing, manipulating and
displaying location information
17 – Magnetic North – The direction of
the north magnetic pole from the
observer’s position, or the direction a
compass points; may not be accurate
18 – True North - The true direction of
the north pole
19 – 2D Operating Mode - A twodimensional GPS position fix that
includes only lat./long.; requires a
minimum of three visible satellites
20 – 3D Operating Mode - A threedimensional GPS position fix that
includes lat./long. and altitude; requires
a minimum of four visible satellites
VI – Operating Garmin Dakota 20
18 Main Menu icons
Map
Where To?
Trip Computer
Active Route
Route Planner
Setup
Main Menu icons continued
Mark Waypoint
Compass
Share Wirelessly
Profile Change
Track Manager
Sun and Moon
Geocaches
Elevation Plot
Waypoint Manager
Calendar
Calculator
Stopwatch
Global Positioning Systems