What is GPS???

1
(No Transcript)
2
What is GPS???

• GPS is short for Global Positioning System
• Most simply, you use a hand held device that
  received signals from satellites in orbit around
  the earth to determine your position on earths
  surface

3
What is GPS???


GPS units
Receive signals from satellites in space
Determine where an object is on earths surface
4
Very Accurate
5
(No Transcript)
6
How do GPS units work??

• The basis of GPS is "triangulation" from
  satellites.
• A GPS receiver measures distance using the travel
  time of radio signals.
• To measure travel time, GPS needs very accurate
  timing which it achieves with some tricks.
• Along with distance, you need to know exactly
  where the satellites are in space.
• Air Force maintains ground control
• Finally you must correct for any delays the
  signal experiences as it travels through the
  atmosphere.

7
(No Transcript)
8
(No Transcript)
9
(No Transcript)
10
Only have 2 points in space where 3 spheres
intersect One will be on earths surface, other
out in space
11
GPS Errors
http//www.trimble.com/gps/errors2.html

• Signals travel at speed of light but not entirely
  true
• Slowed down in Ionosphere charged particles
• Slower down in Troposphere water vapor
• Solution Modeling atmospheric interference, not
  easy, changing constantly

12
GPS Errors

• Multipath errors
• Result when the direct path to your receiver is
  blocked
• House,  roof,  trees, mountains, 
• buildings, etc
• The signal from the satellite is REFLECTED by
  some object. 

13
Differential Correction Eliminate Errors

• Differential correction
• Base station, known position.
• Used to calculate the error in the satellite
  signals.
• Accomplished by finding the difference between
  the positions calculated from the satellite
  signals and the known reference position (base
  station)
• Resulting differential corrections can be used to
  remove much of the error from the rover file
  data.

14
(No Transcript)
15
(No Transcript)
16
Who maintains the satellites??

• U.S. Air Force's 2nd Satellite Operations
  squadron at Falcon AFB in Colorado maintains the
  GPS system
• GPS is a high maintenance system
• Satellites require regular tweaking
• data uploads,
• orbital positioning adjustments
• clock maintenance
• If the ground segment stopped, the system would
  "gracefully degrade" to complete uselessness in
  about two weeks time.
• So, as each satellite whizzes along and completes
  one earth orbit every 12 hours, Air Force
  personnel at Falcon AFB talk to it every few
  hours.

17
Converting Units

• Degrees, Minutes -96, 47.46732 or 44, 27.66789
• -96, 47.46732 -(96 (47.467328/60))
• Decimal degrees -96.791122
• 44, 27.66789 44 (27.66786/60)
• Decimal degrees 44.46113

• Degrees, Minutes, Seconds
• -96, 47, 28.0392
• -(96 (47 /60) (28.0392/3600))
• Decimal degrees -96.791122

18
Converting Units

• 1. Decimal Degrees -96.791122
• -(96 (0 .79112260))
• Degrees, Minutes
• -96, 47.46732
• 2. Decimal Degrees -96.791122
• (-96 (0.791122 60)) -96, 47.46732
• -96, 47, (0.46732 60)
• Degrees, Minutes, Seconds
• -96, 47, 28.0392

19
Accuracy

• Different equipment have different levels of
  accuracy
• Magellan units, less expensive, less accurate,
  Cabelas
• Trimble units, Longitude, Latitude, not so
  accurate in elevation, Ag132
• Trimble RTK units, Longitude, Latitude, very
  accurate in elevation, more expensive

20
Different Use, Different Accuracy, Different
Cost!!

• Magellan units like today
• Cost 200 250
• Accuracy
• Bring you back to within about 90 feet of same
  spot
• Buy many places
• In SD, Cabelas, Scheels
• Uses Fishing, Hunting, Navigation

21
Different Use, Different Accuracy, Different
Cost!!

• IPAQs and GPS receivers
• Agriculture
• Scouting, Collecting GPS for data points
• Record Keeping
• Pocket Excel, Work, Internet
• Accuracy
• About 2 to 5 meters
• Cost 350 for IPAQ, 180 for GPS receiver, 200
  - 400 for GPS software to log points

GPS
22
Different Use, Different Accuracy, Different
Cost!!

• Trimble AG 132 GPS units
• Accuracy 6 to 10 in.
• Cost 3,000
• Trimble Units
• Mapping data

23
Different Use, Different Accuracy, Different
Cost!!

• Real Time Kinematic GPS or RTK GPS
• Survey grade
• Engineering roads
• Navigation
• Fishing
• Airlines
• Agriculture
• Fertilizer or seed applications
• Accuracy
• lt 1 inch
• Cost
• 25,000 to 50,000

24
(No Transcript)
25
(No Transcript)
26
GPS in Agriculture
27
Yield Monitor
28
Mapping Weeds
29
(No Transcript)
30
(No Transcript)
31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
(No Transcript)
35
(No Transcript)
36
Questions