The document discusses key concepts about GPS (Global Positioning System) including: 1. GPS has three segments - the control segment controls the satellites from ground stations, the space segment consists of 24 satellites that transmit signals, and the user segment are the GPS receivers that receive signals to determine location. 2. GPS uses trilateration based on the time it takes signals from multiple satellites to reach the receiver to calculate the user's position. Accuracy depends on factors like receiver quality and atmospheric conditions. 3. Sources of error include satellite and receiver clocks, atmospheric delays, multipath interference, and satellite geometry which is measured by dilution of precision (DOP). Differential GPS can improve accuracy to 1-3 meters.

1. 2 GPS concepts By Mahmoud El Mewafi Mmewafi1@ excite.com Professor of Surveying and Geodesy, Public Works Dept., Faculty of Engineering, Mansoura University, Egypt. Tel 002 0127440767

2. Current Satellite Navigation Systems 1- Global Positioning System (GPS) – USA First Experimental Launch Feb, 1978 First Operational Launch 1989 and Operational Capability in Feb, 1993 2- Global Navigation Satellite System (GLONASS) – Russia

3. Future Satellite Navigation Systems • Galileo – European Union – New services like SAR (Search and Rescue) – Higher Accuracy for Civil Community – Tentative Plan of Launch : 2005 – 2006 – Availability of Service : 2008? • QZSS( Quasi-Zenith Satellite System) – Japan – Basically, communication satellite but also transmit GPS like signals for navigation • Communication • Broadcasting • Navigation

4. GPS (Global Positioning System)

5. Three Segments of the GPS Control Segment Space Segment User Segment Monitor Stations Ground Antennas Master Station

6. Control Segment Kwajalein Atoll US Space Command Hawaii Ascension Is. Diego Garcia Cape Canaveral Ground Antenna Master Control Station Monitor Station

7. Satellites (space segment) 24 NAVSTAR satellites (21 operational and 3 spares) orbit the Earth every 12 hours ~11,000 miles altitude positioned in 6 orbital planes orbital period/planes designed to keep 4-6 above the horizon at any time controlled by five ground stations around the globe

8. Space Segment of GPS GPS satellites are the space segment of the system. These are space vehicles and are responsible for sending radio signals from space. The Space Segment of the system consists of the GPS satellites. These space vehicles (SVs) send radio signals from space. The nominal GPS Operational Constellation consists of 24 satellites that orbit the earth in 12 hours. There are often more than 24 operational satellites as new ones launched to replace older satellites.

9. GPS – User Segment (Receivers) Ground-based devices read and interpret the radio signals from several of the NAVSTAR satellites at once Determine their position using the time it takes signals from the satellites to reach the hand-held unit Calculations result in varying degrees of accuracy that depend on: quality of the receiver user operation of the receiver local & atmospheric conditions current status of system

10. GPS – User Segment (Receivers)

11. Satellites have accurate atomic clocks and all 24 satellites are transmitting the same time signal at the same time The satellite signals contains information that includes Satellite number Time of transmission Receivers use an almanac that includes The position of all satellites every second This is updated monthly from control stations The satellite signal is received, compared with the receiver’s internal clock, and used to calculate the distance from that satellite Trilateration (similar to triangulation) is used to determine location from multiple satellite signals How It Works

12. Position is Based on Time T + 3 Distance between satellite and receiver = “3 times the speed of light” T Signal leaves satellite at time “T” Signal is picked up by the receiver at time “T + 3”

13. GPS theory

14. XYZT

15. Signal From One Satellite The receiver is somewhere on this sphere.

16. Signals From Two Satellites

17. Signals From Two Satellites X? 5 Sec 3 Sec

18. Three Satellites (2D Positioning)

19. 2D-3 Satellites 5 Sec 3 Sec X 4 Sec

20. Three Dimensional (3D) Positioning

21. GPS theory That's right, if three perfect measurements can locate a point in 3-dimensional space, then four imperfect measurements can do the same thing. 1. (X1 - X)² + (y1 - Y)² + (z1 - Z)² = c²(t1 - T)² 2. (X2 - X)² + (y2 - Y)² + (z2 - Z)² = c²(t2 - T)² 3. (X3 - X)² + (y3 - Y)² + (z3 - Z)² = c²(t3 - T)² 4. (X3 - X)² + (y3 - Y)² + (z4 - Z)² = c²(t4 - T)²

22. GPS signal structure L1 Band Frequency = 154 x 10.23 MHz = 1575.42 MHz – C/A Code at 1.024Mhz – P Code at 10.23 Mhz – Navigation Data at 50Hz L2 Band Frequency = 120 x 10.23 MHz = 1227.60 MHz – P Code at 10.23Mhz or – Encrypted P Code called Y Code at 10.23Mhz – Navigation Data Bit at 50Hz Clock Frequency : 10.23MHz

23. Characteristics of GPS Signal • C/A (Coarse Acquisition) Code – Also called PRN (Pseudo Random Numbers) – PRN codes are unique for every satellite – All the Satellites have the same frequency – Modulation is done by using CDMA which is a technology based on Spread Spectrum – Spread Spectrum gives wider bandwidth – Signal is spread and hence is below the noise floor – Difficult to intercept – Requires Low power – Efficient use of Frequency Spectrum • P Code – Encrypted using Encryption Code – Encrypted P code is called Y code – Used basically for Military purpose – Higher Accuracy – Extremely difficult to intercept – A very complex code

24. Generation of L1 Band Signal

25. Error Sources • Satellite Clock Error • Ephemeris Error – Satellite Orbit and Satellite Related • Atmospheric Propagation Delay – Ionospheric Delay – Tropospheric Delay • Receiver Noise – Receiver Clock (Oscillator Noise) – Thermal Noise – Device Induced Interference • Multipath – Surrounding Environment • Satellite Geometry – DOPs

26. Sources of GPS Error Standard Positioning Service (SPS ): Civilian Users Source Amount of Error Satellite clocks: 1.5 to 3.6 meters Orbital errors: < 1 meter Ionosphere: 5.0 to 7.0 meters Troposphere: 0.5 to 0.7 meters Receiver noise: 0.3 to 1.5 meters Multipath: 0.6 to 1.2 meters Selective Availability (see notes) User error: Up to a kilometer or more Errors are cumulative and increased by PDOP.

27. Atmospheric Delays As a GPS signal passes through the charged particles of the ionosphere and then through the water vapor in the troposphere it gets slowed down a bit, and this creates the same kind of error as bad clocks.

28. Multipath Sources of Signal Interference Earth’s Atmosphere Solid Structures Metal Electro-magnetic Fields

29. Receiver Errors are Cumulative! User error = +- 1 km System and other flaws = < 9 meters

30. DOP is the Geometric Orientation of Satellites with respect to the Antenna

31. GPS Satellite Geometry Satellite geometry can affect the quality of GPS signals and accuracy of receiver trilateration. Dilution of Precision (DOP) reflects each satellite’s position relative to the other satellites being accessed by a receiver. There are five distinct kinds of DOP. Position Dilution of Precision (PDOP) is the DOP value used most commonly in GPS to determine the quality of a receiver’s position. It’s usually up to the GPS receiver to pick satellites which provide the best position triangulation. Some GPS receivers allow DOP to be manipulated by the user.

32. Ideal Satellite Geometry N S W E

33. Good Satellite Geometry

34. Good Satellite Geometry

35. Poor Satellite Geometry N S W E

36. Poor Satellite Geometry

37. Poor Satellite Geometry

38. GPS Navigation: On the Ground Active GOTO Waypoint Location Where GOTO Was Executed Bearing = Course Over Ground (COG) = Cross Track Error (XTE) = Bearing = 65 0 COG = 5 0 XTE = 1/2 mi. Bearing = 78 0 COG = 350 0 XTE = 1/3 mi. Bearing = 40 0 COG = 104 0 XTE = 1/4 mi. Active Leg N

39. Position Fix A position is based on real-time satellite tracking. It’s defined by a set of coordinates. It has no name. A position represents only an approximation of the receiver’s true location. A position is not static. It changes constantly as the GPS receiver moves (or wanders due to random errors). A receiver must be in 2D or 3D mode (at least 3 or 4 satellites acquired) in order to provide a position fix. 3D mode dramatically improves position accuracy.

40. Waypoint A waypoint is based on coordinates entered into a GPS receiver’s memory. It can be either a saved position fix, or user entered coordinates. It can be created for any remote point on earth. It must have a receiver designated code or number, or a user supplied name. Once entered and saved, a waypoint remains unchanged in the receiver’s memory until edited or deleted.

41. Planning a Navigation Route Start = Waypoint

42. How A Receiver Sees Your Route

43. GPS Waypoint Circle of Error X

44. GPS Survey Observation • Static Observation – Antenna is fixed at a point – Gives higher accuracy since observation is done for long time period • Average of the observation cancels out some errors – Only Code Phase Observation – A few meters level accuracy • Kinematic Observation – Antenna is moving – Just a few or single epoch observation at a particular point – Accuracy is lower – Only Code Phase Observation – Sometimes error is too large, few hundreds of meters

45. Single GPS Survey Observation • Static Observation – Antenna is fixed at a point – Gives higher accuracy since observation is done for long time period • Average of the observation cancels out some errors – Only Code Phase Observation – A few meters level accuracy • Kinematic Observation – Antenna is moving – Just a few or single epoch observation at a particular point – Accuracy is lower – Only Code Phase Observation – Sometimes error is too large, few hundreds of meters

46. Differential GPS (DGPS) Survey Observation • At least one base station and one rover is necessary • Both Base station and rover logs the data at the same time or use the same time data for processing • Data link must be available for real time DGPS • DGPS has been widely used in many applications where accuracy is anissue 1- Static Observation 2- Kinematic Observation

47. GPS - Differential Correction GPS error when using differential correction: 1 – 3 meters There are two ways that differential correction can be applied: Post-processing differential correction Does the error calculations after the rover has collected the points Real-time differential correction Done in real time by receiving a broadcasted correction signal (usually expensive), requiring other hardware (not just a consumer GPS receiver)

48. Real Time Differential GPS True coordinates = x +0, y +0 Correction = x -5, y +3 DGPS correction = x +(30-5) and y +(60+3) True coordinates = x +25, y +63 DGPS Site x +30, y +60 x +5, y -3 x -5, y +3 DGPS Receiver Receiver

49. Differential Correction 2 10m 10m Base Station (w/known coordinates) Receiver (unknown Location) GPS Receiver Estimated Location Differentially Corrected Estimated Position GPS Estimated Location Actual (Known) Position

50. Differential GPS (DGPS) • Base Station – Base Station is located at a known Point – The point is surveyed by other means of measurement – Base Station Data are broadcasted using radio channel or telephone line for real time DGPS – Base Station Data are also recorded on a PC for post processing of rover data

51. Rover Station • Rover or Field Station – Field unit observes GPS data – For Realtime DGPS, a data antenna or telephone line is used to receive the base station log data – For post processing, the field data is brought back to the office and post processed in the computer using Base station data

52. Advantage of GPS surveys • Three Dimensional • Site Intervisibility Not Needed • Weather Independent • Day or Night Operation • Common Reference System • Rapid Data Processing with Quality Control • High Precision • Less Labor Intensive/Cost Effective • Very Few Skilled Personnel Needed

53. 12. What is the fastest initialization method ? 13. How much data is collected at each point in stop-and-go GPS surveying ? 15. What are the time limitations on re-occupation ? 16. Which GPS surveying method would you use for establishing control with geodetic accuracy ? 17. Which GPS surveying method would you use if you need to complete a job urgently

54. Wide Area Augmentation System Geostationary WAAS satellites GPS Constellation WAAS Control Station (West Coast) Local Area System (LAAS) WAAS Control Station (East Coast)

55. How good is WAAS? With Selective Availability set to zero, and under ideal conditions, a GPS receiver without WAAS can achieve fifteen meter accuracy most of the time.* Under ideal conditions a WAAS equipped GPS receiver can achieve three meter accuracy 95% of the time.* * Precision depends on good satellite geometry, open sky view, and no user induced errors. + - 3 meters +-15 meters

56. QUESTIONS 1. What are the advantages of GPS surveying over conventional surveying methods ? 2. What is the single factor that determines whether or not a GPS survey is possible in an area and/or a project ? 3. What is a ‘baseline’ in GPS surveying ? 5. What is an ‘epoch’ in GPS terminology ? 6. Why is the ‘static’ GPS survey method so named ? 7. What is the reason for ‘minimum session length’ in static surveying ? 8. What factors determine the length of a session in static surveying ? 9. What factors determine the GPS surveying method suitable for a given area/project ? 10. What is the purpose of rover ‘initialization’ in kinematic surveying ?

57. The End

58. GPS Applications Generating mapped data for GIS databases “ traditional” GIS analysts & data developers travel to field and capture location & attribute information cheaply (instead of surveying) Other uses (many in real time ): 911/firefighter/police/ambulance dispatch car navigation roadside assistance business vehicle/fleet management mineral/resource exploration wildlife tracking boat navigation Recreational Ski patrol/medical staff location monitoring

59. Validation Accuracy Turnaround time Cost Client response Developers’ response?

60. GPS Applications Generating mapped data for GIS databases “ traditional” GIS analysts & data developers travel to field and capture location & attribute information cheaply (instead of surveying) Other uses (many in real time ): 911/firefighter/police/ambulance dispatch car navigation roadside assistance business vehicle/fleet management mineral/resource exploration wildlife tracking boat navigation Recreational Ski patrol/medical staff location monitoring

61. Computers In Law Enforcement Officers today usually have a laptop available in their vehicles with wireless Internet to Write tickets Fill out accident reports Complete routine police work Download criminal and driving records from databases Check license plate registrations Retrieve information from headquarters while on the road

62. Challenges and Problems “ We can have more data available than ever; how can we use it effectively for law enforcement?” “ How can we combat stolen vehicles in our community?” “ How can our officers run more license plate checks and still do their other duties?” “ How can we increase our officers’ safety when they’re patrolling and making traffic stops?”

63. ALPR Mobile Vehicle Solution Up to two exterior cameras, mounted on roof or light bar Fixed focal length lenses for different use cases Manual updates to database in the field Back Office Utility software for easy data management Global Positioning System (GPS) and Mapping Support Integration with Mobile Video Enforcer (MVE) Alert triggers MVE recording AirMobile and MESH / 802.11 integration for wireless updates of local database Certified for Motorola MW800 / ML900 / ML850 / Panasonic Toughbook CF-29

64. Applications – Amber Alert Tracking Application Mobile unit equipped with a single camera. Officer can update database manually through PAGIS. Benefit Increase effectiveness of response to alerts May save lives Automatic reading of licenses in the background

65. Case Study Pennsylvania State Police Pilot - Background Profile Pennsylvania State Police are installing 1400 MW800’s Mobile Data Terminals (MDTs) Colonel saw technology in Europe 22,000 stolen cars a year in PA Customer likes trying new technology and giving feedback Pilot components 6 patrol cars out of Harrisburg 3 shifts / 6 weeks Broad “hot list” with CLEAN, NCIC, local wants and warrants

66. Case Study Pennsylvania State Police Pilot - Results Immediate Results Vehicle recovered in the first shift Sgt. Franks DeAndrea: “If we would end the test today, it would already be a full success.” Armed and dangerous suspects apprehended in the first week Officer safety reinforced Official report: “The trooper feels the ALPR system saved his life and prevented a serious incident from occurring.” Click here to view the ABC News Clip with details

67. Tracking Evidence Police may enter documentation about evidence into a handheld computer Wirelessly transmits the information to an evidence database Prints out a bar code sticker that is placed on the physical evidence DNA evidence is stored in the CODIS (Combined DNA Index System) database Forensic and offender indexes Fingerprint evidence is stored in the AFIS (Integrated Automated Fingerprint Identification System) database Fingerprint images are scanned electronically

68. Storing Criminal Records NCIC (National Crime Information Center) FBI database of criminal justice information Officers check subject’s previous record after arrest NICS (National Instant Criminal Background Check System) FBI system to help gun dealers perform background checks on potential buyers Dealer calls the Bureau of Identification to run a query on several databases

69. Online Criminal Database

70. Enforcing Traffic Laws Red-light systems use computer technology to catch drivers who run red lights Cameras are positioned at intersection corners A sensor loop triggers if a car moves over a certain speed The software activates the cameras to take photos The software then creates a record with the time, location, and the photos, and a citation is sent to the offender Traffic violation fines may often be accessed and paid online

71. Tracking Stolen Vehicles LoJack is a stolen vehicle recovery system A wireless radio-frequency transmitter is placed in the car The vehicle identification number of a stolen vehicle is checked against the NCIC (National Crime Information Center) A signal can be sent to the device, which much like a GPS reports its exact location / a map can be created Key pass theft system Uses a motion sensor and uniquely coded key pass to detect unauthorized motion of a vehicle

72. Finding Missing Children Amber Alert system Immediately notifies public for help in recovering missing children Uses EAS (Emergency Alert System) technology EAS broadcasts alert on radio and television Alerts can be displayed on dynamic message signs on highways NCMEC (National Center for Missing and Exploited Children) provides alerts via e-mail, mobile phone, pager, or AOL Instant Messenger

74. Providing Wireless 911 Enhanced 911 (E-911) displays phone number and address information on operator’s computer The ANI (automatic number identifier) and ALI (automatic location identifier) databases provide the information ANI and ALI does not work with cell phones FCC (Federal Communications Commission) requires that all cell phone providers equip phones with GPS (global positioning system) receivers GPS receiver receives signals from GPS satellite Computer links this information to the ALI database

75. VeriChip Implantable microchip that stores personal information Useful for tracking people with illnesses or in danger Raises privacy and legal issues

76. Garmin’s cheapest receivers Garmin’s iQue 3600 PDA: http://www.garmin.com/products/iQue3600/ Garmin’s Forerunner 201: A watch that uses GPS to determine current speed, average speed, exact distance traveled, etc. ( ) Basic features also available in the Forerunner 101 ($115). http://www.garmin.com/products/forerunner201/

77. Garmin GPSmap60-C Main Screens Time & Date

78. Garmin GPSmap60-C Satellite Page Location Satellite Strength Accuracy Estimate Skyplot

79. Garmin GPSmap60-C Mark Waypoint Name Symbol Average

80. Garmin GPSmap60-C Main Screens Setup By default, the GPSmap60 will record a Track (line feature) whenever the unit is turned on. Map (GoTo) Profiles

81. Bluetooth GPS Receivers Teletype’s Mini-bluetooth GPS receiver ($175) http://www.mightygps.com/Manufacturer/minibluetooth.htm Teletype’s USB GPS receiver for Laptops ($170) http://www.teletype.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=1250&Category_Code=

82. HP’s Ipaqs and other PDAs with GPS software Hewlett-Packard’s new iPAQ h1945 PDA Now comes equipped with a hp GPS receiver and navigation system ($500) http://www.shopping.hp.com/cgi-bin/hpdirect/shopping/scripts/product_detail/product_detail_view.jsp?BV_SessionID=@@@@0280349227.1102102313@@@@&BV_EngineID=ccckadddfdjlkdgcfngcfkmdflldfgg.0&landing=null&category=handhelds&subcat1=classic_performance&product_code=PF527A%23ABA&catLevel=3 Garmin’s iQue 3600 PDA: http://www.garmin.com/products/iQue3600/

83. The End

84. GPS – Ellipsoid - Datum GPS uses the WGS84 (World Geodetic System of 1984) as mathematical surface (model) of the earth Elevations are referenced to Height Above Ellipsoid (HAE)

85. Navigation Review Position on the earth is measured in terms of latitude and longitude Parallels of latitude define position in the north-south direction Latitude is measured as angle from center of earth north or south o o o o 70 50 30 0

86. Navigation Review Longitude is defined as an angle, east or west of a reference meridian passing through Greenwich, England Every point on the earth has a unique address in terms of latitude and longitude Greenwich W E

87. Lat: 40 N Lo: 20 W 60 N 40 N 20 N 20 S 40 S 60 S Equator Prime Meridian 20 W 20 E Lat: 40 00’.00N Lo: 020 00’.00W Lat: 40 00’.00S Lo: 020 00’.00W Every place on earth has a unique location 180 Lo approx. International Date Line o o o O o o o o o o o o o o o

88. 60 04’ .20” N 149 26’.10” W o o 60 o 05’ 149 30’W o 20’

89. Navigation Review Horizontal datum is a chart coordinate reference system Nautical charts are in the process of being standardized, not all are drawn to the same datum The datum is shown on each chart GPS receivers must be adjusted to the same datum as used on the chart!

90. By Mahmoud El Mewafi Mmewafi1@ excite.com Professor of surveting and Geodesy, Public Works Dept., Faculty of Engineering, Mansoura University, Egypt 6 Datum Transformations

91. سطوح المقارنة لكل من الكرة الأرضية ونظام الجي بي اس وعملية تحويل القياسات بينهما Sat. 2 Receiver X Z Y (0, 0, 0) WGS-84 Local Sat. 3 Sat. 1 Sat. 4

92. Datum Transformations A number of different procedures are available for performing coordinate transformations 1. Helmert T ransformation 2. Molodenskii T ransformation 3. Multiple Rregression Transformation

93. Helmert Transformations The most general method of transforming coordinates from one geodetic datum to another uses all 7 geometrical transformation parameters to convert Cartesian coordinates (X, Y and Z). The general formulation of this transformation is : Where X1, Y1, Z1 Cartesian coordinates in first datum X2, Y2, Z2 Cartesian coordinates in second datum. The rotation angles θ x , θ y and θ z, expressed in radians in the matrix, are assumed ’small’ angles, i.e. of the order of a few seconds-of-arc

94. the geodetic coordinates ( Φ , λ , h) of a point it is first necessary to convert these to Cartesian coordinates, before the transformation can be applied. Similarly, the resulting coordinates in the new datum could also be converted to the corresponding geodetic latitude and longitude using the parameters of the ellipsoid associated with this new datum.

95. The End