What is GPS?

2. What is GPS? GPS, which stands for Global Positioning System, is the only system today able to show you your exact position on the Earth anytime, in any weather, anywhere. The three parts of GPS are: • Satellites • Receivers • Software

3. GPS Uses • Police and Emergency Medical Services • Firefighters   • Map makers • Science 

4. Satellites There are quite a number of satellites out there in space. They are used for a wide range of purposes: satellite TV, cellular phones, military purposes and etc. Satellites can also be used by GPS receivers.

5. GPS Units Today 1970s

6. GPS Satellites The GPS Operational Constellation consists of 24 satellites that orbit the Earth in very precise orbits twice a day. GPS satellites emit continuous navigation signals.

7. Receivers and Satellites GPS units are made to communicate with GPS satellites (which have a much better view of the Earth) to find out exactly where they are on the global scale of things.

8. Speed of Sound Count the seconds between the lightning and the thunder, then divide by 5.

9. GPS Signals Each GPS satellite transmits data that indicates its location and the current time. All GPS satellites synchronize operations so that these repeating signals are transmitted at the same instant. Physically the signal is just a complicated digital code, or in other words, a complicated sequence of “on” and “off” pulses.

10. Time Difference 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. Satellite transmits at 11:00:00 GPS unit receives at 11:00:05

11. Calculating Distance Velocity x Time = Distance Radio waves travel at the speed of light, roughly 186,000 miles per second (mps) If it took 0.06 seconds to receive a signal transmitted by a satellite floating directly overhead, use this formula to find your distance from the satellite. 186,000 mps x 0.06 seconds = 11,160 miles

12. Triangulation Geometric Principle: You can find one location if you know its distance from other, already-known locations.

13. Triangulation

14. Triangulation

15. 3-D Trilateration 1 Satellite 2 Satellites 3 Satellites

17. Latitude and Longitude Latitude Longitude Elevation

19. Longitude (West) 150 ° 140 ° 130 ° 120 ° 110 ° 100 ° 90 ° 60° 50 ° 40 ° 30 ° 20 ° 10 ° 0 ° X Latitude (North) X X X X

20. Line-of-sight Line of sight means the GPS unit needs to be in a visible line with the GPS satellites.

21. 3 2 1 4 B A 5

22. Light Refraction Sometimes the GPS signal from the satellite doesn’t follow a straight line. Refraction is the bending of light as it travels through one media to another.

23. WAAS SystemWide Area Augmentation System WAAS is a system of satellites and ground stations that provide GPS signal corrections, giving five times better position accuracy.

24. On Screens

25. Mark

26. Waypoint

27. Signal Refraction Signals from satellites can be like light. When they hit some interference (air patterns in the atmosphere, uneven geography, etc.) they sometimes bend a little.

28. Signal Interference Sometimes the signals bounce off things before they hit the receivers.

29. Satellite Distribution When the satellites are all in the same part of the sky, readings will be less accurate.

30. PDOP PDOP = Positional Dilution of Precision All of this combines to make the signal less accurate, and gives it what we call a high “PDOP.” 11,000 miles 11,000 miles 11,000 miles 11,000 miles • A PDOP of <4 is excellent • A PDOP of 4-8 is good • A PDOP of >8 is poor

31. GPS Unit Enter Navigate Power

32. Satellite Screen

33. Map Screen You are here IN OUT

34. Compass Screen

35. Waypoints Waypoints are locations or landmarks worth recording and storing in your GPS. These are locations you may later want to return to.

36. GOTO Waypoint • Menu button • GOTO option • User Waypoint • Position • Select waypoint • Use Compass or Road screen to navigate back to waypoint.

38. Differential Correction Differential correction is a technique that greatly increases the accuracy of the collected GPS data. It involves using a receiver at a known location - the "base station“- and comparing that data with GPS positions collected from unknown locations with "roving receivers." ISU Base Station - http://134.50.65.125/

39. Postprocessing / Real-time Before After

40. In a Nutshell

41. Trimble GeoExplorer 3 EXTERNAL ANTENNA HOOKUP SCREEN ENTER button lets you select an option OPTION button displays choices and menus in the various screens CLOSE button lets you cancel a feature or close a menu box ARROW BARS let you scroll up/down and left/right SYSTEM button lets you scroll through the various system screens NAVIGATION button lets you scroll through the different navigation screens FUNCTION button is for working with system and configurations DATA button lets you scroll between the various data screens BATTERY COMPARTMENT POWER button turns power on and off LOG button allows you to pause/unpause satellite communication for a time

42. System • See how many satellites are in communication • Check level of memory and battery power • Change data collection settings

43. Data • Data collection stored. • Features updated • Map of features • New features added

44. Navigation • Maps to show where you are in relation to the place you’re trying to get to. • How fast you’re walking or driving • How far you’ve gone

45. Collecting Data • Circle represents horizon • Numbers in circle represent satellites within horizon • Black squares are locked-in satellites. • White squares are satellites not locked in. • No squares are satellites not communicating. Need a minimum of four satellites.

46. “Too few satellites” • Just a bad time of day. • PDOP is set too high. (Hit Sys button twice)

47. More System Tools • Number of satellites • Blinking number means not enough satellites • Battery Level These tools are always open no matter what screen you are in.

48. Data Screen Name your file Don’t change the first letter Choose your data dictionary

49. Data Dictionary GPS units collect data in: • Points • Lines • Areas These are called features. A data dictionary is a means by which we collect specific information about a data feature.

50. Road Signs Fire Hydrants Macro Art Roving File A roving file is like a drawer of a filing cabinet containing many feature files. Collect all the features collected in one interval in one roving file.