GPS FUNDAMENTALS FOR LAND SURVEYORS AND GIS PROFESSIONALS by sanmelody

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									    GPS Fundamentals
    FOR SURVEYING, GIS AND CONSTRUCTION PROFESSIONALS




1
    GPS OVERVIEW


      The Global Positioning System
        – Managed by the U.S. Department of Defense
        – Worldwide satellite-based radio-navigation tool
      Satellites transmit on two L-Band radio frequencies
          (L-Band frequencies range from 950 to 2150 MHz)
        – L1 @ 1575.42 MHz
        – L2 @ 1227.60 MHz
      Two service levels
        – Precise Positioning (PPS)
        – Standard Positioning (SPS)


2
    GPS HISTORICAL HIGHLIGHTS


       1957: Russia launches first satellite “Sputnik”

       1958: U.S.A. launches “Explorer 1”

       1974: U.S.A. launches first GPS satellite

       1991: First military use of GPS in Desert Storm

       1995: Full Operational Capability

       2000: Selective Availability turned off

       2005: GPS Modernization effort launched

3
    GLOBAL NAVIGATION SATELLITE SYSTEMS


               • Russia has developed a Global Navigation
               Satellite System (GNSS) called GLONASS

               ГЛОНАСС; ГЛОбальная НАвигационная
               Спутниковая Система
               Global'naya Navigatsionnaya Sputnikovaya
               Sistema
                   • The European Union is developing a
                   GNSS called Galileo. Plans are for the
                   system to be operational in 2012.



4
    GPS MERGING TECHNOLOGIES

       Space System Reliability
        – The earlier Transit satellites were designed to last 2-3 years.
          Some of these satellites operated for over 25 years.
       Atomic Clock Hardware
        – Reliable, stable, compact and space qualified atomic frequency
          oscillators allows for the autonomous, synchronized generation
          and transmission of accurate timing signals by each satellite
          without continuous monitoring from the ground.
       Satellite Tracking and Orbit Determination
        – Ground tracking feasibility and accurate orbit prediction
          techniques.
       Spread Spectrum Technology
        – Able to track relatively low signal strength in the presence of
          considerable ambient noise.
       Very Large Scale Integrated (VLSI) Circuits
        – Low cost, low power consumption with powerful computing
          capabilities.

5
    GPS COMPOSITION


     •   SPACE COMPONENT
         – The network or constellation of satellites circling the globe.

     •   GROUND COMPONENT
         – Master Control Station
         – Monitoring Stations
         – Ground Antennas

     •   USERS
         – Antennas/Receivers utilizing the radio-navigation signals.




6
    GPS SATELLITE GENERATIONS


       BLOCK I
        – 1975-1985, SVN’s 1-11, testing generation

       BLOCK II
        – 1989-1990, SVN’s 13-21, 14 days with no contact from Control
          Segment (CS), 7.3 years design life

       BLOCK IIA
        – 1990-1997, SVN’s 22-40, 14 days no CS contact, 180 days of
          autonomy (AUTONAV), 7.3 years design life

       BLOCK IIR
        – 1997 – Present, SVN’s 41-62, 14 days no CS contact, 180
          days of AUTONAV, 7.8 years design life, crosslink
          communications between satellites



7
    GPS SATELLITE GENERATIONS (Cont.)


        BLOCK IIR-M (Block IIR Modernized)
         – 2005 – Present, a second civilian signal L2C added to the L2
           carrier frequency, a military signal (M-Code) added to L1 and
           L2 frequencies.

        BLOCK IIF (Block II Follow-on)
         – First scheduled launch in 2008, 12 years design life, M-Code,
           L2C and L5 (a third civil signal on a frequency of 1176.45
           MHz).

        BLOCK III
         – Being planned for deployment no sooner than 2012, these
           satellites will offer all of the features above but will also add
           anti-jamming technology and selective service capabilities
           where the GPS signal can be deactivated in targeted regions.


8
    GPS SATELLITE FACTS

       Average weight: 2200 lbs (998 kg)
       Power Source: Solar panels
       Dimensions: 5’ x 6’ x 5’ plus 38 foot wingspan
                   (1.52m x 1.83m x 1.52m, wing = 11.58m)
       Cesium clocks on each satellite need to be recalibrated
        twice per year. Each calibration requires approximately
        18 hours of unusable satellite time.
       Satellites need to be repositioned one time each year to
        return it to its original orbit. This maneuver, called
        “Delta-V” requires approximately 12 hours of unusable
        satellite time.
       It takes between 65 and 85 (0.065 – 0.085) milliseconds
        for a satellite signal to reach the earth.
     Block II satellites use nickel-hydrogen or nickel-
      cadmium batteries.
9
     GPS SATELLITES CONFIGURATION


       11 hours 58 minutes
        orbital period (1.8 miles
        per second)
         At least 4 Satellites                   60°
          always visible any
          place on the planet                           55°

                                    Equator
         24 hour 3D coverage
          worldwide
         20,200 kilometers high
          (3 times the Earth’s
          radius)
         27 Active Satellites
         6 Orbital Planes                Satellite distribution
                                          in an orbital plane

10
     GPS GROUND COMPONENT

        The ground based control component is known as the
         Operational Control Segment (OCS):




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           GPS SIGNAL CHARACTERISTICS

           Fundamental                          Navigation Message on L1 @ 50 bps
            Frequency
            10.23 MHz                                                                            x .10

                                   L1 Carrier 1575.42
                                                                P-Code                   CA Code
                                          MHz
                                                               10.23 MHz                1.023 MHz
                     x 154          19cm wavelength
                                      M-Code (IIR-M)
                                                            29.3m wavelength         293m wavelength

                                      L2 Carrier                    P-Code                Block IIF
                                     1227.60 MHz                   10.23 MHz
                                                                                         L1, L2, L2C
                     x 120         24cm wavelength                                            +
                                                                29.3m wavelength     L5 on 1176.45 MHz
                                   L2C & M-Code (IIR-M)

            Carrier provides information every
              19 & 24cm with no time tags.
                                                                           Code provides time tagged
                                                                            information every 293m
              X              X                   X
     10c      20c    30c     40c        50c      60c
      m        m      m       m          m        m       100        200     300    400    500           600
                                                           m          m      X
                                                                             m       m      m            Xm

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         GPS USERS


         Land, Sea, Air Navigation      Recreational Uses
          –   Aviation                    – Hiking
          –   Marine navigation           – Geocaching
          –   Fleet management            – Points Of Interest
          –   Public safety              Timing
          –   Rail                        –   Time transfer
         Surveying and Mapping           –   Financial transactions
          – Civil Engineering             –   Cellular networks
          – GIS                           –   Electrical power grids
          – Agriculture                  Scientific Research
         Military Applications           –   Environmental studies
          – Target designation            –   Tectonic movement detection
          – Smart weapons                 –   Deformations
          – Air support                   –   Geo-fencing

13
         GPS NEEDS SKY

     •   At least 4 visible satellites needed to compute 3D position.




14
     ERROR SOURCES

         •   Ephemeris Data: GPS message does not transmit the
         satellites’ correct location

         •   Satellite Clock Error: Including Selective Availability (SA)

         •   Ionosphere: GPS signal is delayed in proportion to the
         number of free electrons

         •   Troposphere: Variations in temperature, pressure and
         humidity cause GPS signal delay

         •   Multipath: Reflected signals

         •   Receiver Measurement: Thermal noise, software accuracy,
         channel bias

         •   User: Data, methodology and settings
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     ERROR SOURCE TABLE

                          MINIMIZED OR          MINIMIZED OR ELIMINATED        *ERROR
     ERROR SOURCE       ELIMINATED WITH            WITH DIFFERENTIAL      CONTRIBUTION (M)
                        DUAL FREQUENCY                CORRECTION            L1 C/A (no SA)
      EPHEMERIS                 NO                       YES                    ± 2.5
        DATA

       SATELLITE
        CLOCK                   NO                       YES                    ± 2.0


      IONOSPHERE                YES                    MOSTLY                   ± 5.0


     TROPOSPHERE                YES                    MOSTLY                   ± 0.5


      MULTIPATH                 NO                        NO                    ± 1.0


       RECEIVER                 NO                        NO                    ± 1.0


           USER                 NO                        NO                    ???

       http://www.kowoma.de/en/gps/errors.htm
       *


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     DIFFERENTIAL GPS


     •   Differential GPS (DGPS) is accomplished by
     using two GPS receivers simultaneously.
     •   DGPS can be carried out in a Post-Processing or
     Real-Time mode.
     •   Many countries provide DGPS services for
     coastal navigation and aviation use.
     •   Local DGPS services are provided by many public
     sectors through GPS reference station networks.
     •   User’s set up their own reference station.

17
     WORLDWIDE SBAS SERVICES

       WAAS (Wide Area Augmentation System) managed by the
      FAA.

       EGNOS (European Geostationary Navigation Overlay
      Service) managed by the European Space Agency.


       MSAS (Multi-functional Satellite Augmentation System)
      managed by the Japanese Multi-functional Transport Satellite
      (MTSAT).

       GAGAN (Sanskrit word meaning Sky) planned for
      implementation in India.

       PRIVATE DGPS SERVICES Omnistar, Fugro, Starfire, CORS.


18
     WORLDWIDE SBAS SERVICES




19
     LOCAL AREA AUGMENTATION SYSTEM (LAAS)
         LAAS (Also called GBAS, Ground Based Augmentation System)
          – 20 – 30 mile (32 – 48 km.)
            radius
          – Precision departures and
            approaches
          – Precise terminal area
            operations
          – Sub-meter 3D
          – Four ground based GPS
            reference receivers at each
            airport
          – Begin deployment in 2008
          – Robust differential
            corrections via VHF radio
            data link.


20
     GPS COORDINATES

        World Geodetic System of 1984 (WGS84)
         – A mathematical ellipsoidal model that best fits the earth (from
           a U.S. perspective). Any other coordinates that are displayed
           are derived from WGS84 values.



                                      b

                                            a


                                                    a = Semi major axis
     a = 6,378,137m                                 b = Semi minor axis
     1/f = 298.25722312                             f = a-b = Flattening
                                                         a
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     GPS COORDINATES

        Earth Centered-Earth Fixed (ECEF) System
         – Also called Cartesian (X,Y,Z) coordinates, are converted to
           Latitude, Longitude, Ellipsoidal height. All values are geo-
           referenced to the center of the model.




                                                D
                                            Z
                                                X
                                                        D
                                                        Z
                                                    D
                                                    Y         X


                                        Y




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       GPS COORDINATES
        • Ellipsoidal Heights are the differences between the
        observed elevation and the ellipsoidal surface.


     WGS84                                     •  Orthometric (sea-level)
                                               Elevations are computed
                                               using the difference
                                               between the surfaces of
                                               the ellipsoid and the
                                               geoid model.
                   Earth Mass
                    Center




                                          GEOID

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     GPS COORDINATES


     Orthometric Height (H) = Ellipsoidal Height (h) – Geoid Height (N)




                              H                    TOPOGRAPHIC SURFACE
                                  h

                                      N

                                          Geoid
      Ellipsoid



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     GPS COORDINATES




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     GPS COORDINATES


       Localizations: Converting ECEF derived
        coordinates into numbers that can be used
        locally.
         – Translations move a set of coordinates a fixed distance
           in a given direction. The original data set and its
           translation have the same dimensions and orientation.

         – Transformations are normally used to transform
           coordinates from WGS1984 to a local system or vice
           versa.




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      GPS COORDINATES
                                          Four points hold a position,
     One-Step Transformation              define the rotation and
                                          scaling and produces
     One control point                    horizontal and vertical
      holds a position                   residuals.
                                                            
      and assumes a
       geodetic north
             rotation.            Project Area


                                                   Three points hold a
                                                   position, define the
      Two control points hold                      rotation and scaling,
        a position and define                    establish a plane
     the rotation and scaling                      surface and
                                                   produce horizontal
                                                   residuals.
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     GPS COORDINATES
                       Z
     Mapping Planes




                           X



            Y



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     GPS COORDINATES

     PROJECTIONS
         Map Projections contain the parameters required to display
          a curved surface on a flat sheet. This results in some type
          of distortion.

         Projections attempt to minimize the distortion on the map in
          the following ways:

          – Conformality: Local shape preservation. Orthomorphic

          – Distance: Preserving distances between points

          – Direction: Preserving directions from a central point

          – Scale: Scaled distances on the map are the same as on
            the Earth
          – Area: Preserving areas. Equal-area. Authalic
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     GPS COORDINATES

     PROJECTIONS
       Creating Map Projections:

         – Select a Spheroidal or Ellipsoidal model of the
           Earth

         – Transform spherical or geodetic coordinates to
           plane coordinates

         – Calculate the scale difference between planar
           and ground distances



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     GPS COORDINATES

     PROJECTIONS
        Selecting best Projection type:
         – Choose the projection that minimizes the distortion of
           the metric for which the map will be primarily used. (i.e.
           distance, area, direction, etc.)
         – Determine orientation of projection to maximize map
           utility
         – Determine desired scalar properties:
              – Scale depends on location, not direction (conformal)
              – For a given latitude and longitude, scale is the same
                (cylindrical)
              – Scale depends on latitude, but not longitude
                (Mercator)
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     GPS COORDINATES

     PROJECTION TYPES
        Cylindrical


        Pseudo-Cylindrical


        Conic


        Azimuthal


        Miscellaneous

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     GPS COORDINATES
                                       Conic:
     PROJECTIONS
                                        – Albers Equal Area
         Cylindrical:
                                        – Equidistant
          – Equal Area
                                        – Lambert Conformal
          – Mercator
                                        – Polyconic
          – Miller
          – Oblique Mercator           Azimuthal
          – Transverse Mercartor        – Equidistant
                                        – Lambert Equal Area
         Pseudo Cylindrical:
                                        – Orthographic
          – Mollweide
                                        – Stereographic
          – Eckert
          – Robinson                   Miscellaneous
          – Sinusoidal Equal Area       – Un-projected Maps
                                        – Space Oblique Mercator
33
     GPS COORDINATES

     PROJECTION EXAMPLES
       Un-projected World Map




34
     GPS COORDINATES

     PROJECTION EXAMPLES
       Universal Transverse Mercator (UTM)




35
     GPS COORDINATES

     PROJECTION EXAMPLES

      New York State
        – Lambert
          Conformal
          Conic_2SP for
          Long Island

        – Transverse
          Mercator for
          other zones in
          the state


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     GPS COORDINATES

     PROJECTION EXAMPLES
       Van der Grinten




37
     GPS COORDINATES

     PROJECTION EXAMPLES
       Mercator




38
     GPS COORDINATES

     PROJECTION EXAMPLES
       Europe




39
     GPS COORDINATES

     EPOCHS
       – Pangaea




40
     GPS COORDINATES

     EPOCHS
       – Movement throughout the world




41
     GPS COORDINATES

     EPOCHS
       – A look at Southern California


             2010

                    2001




                            1993


                              1984




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     GPS COORDINATES

     EPOCHS

      – Dilemma

        – The international community desires a global
        reference system (International Terrestrial
        Reference Frame or ITRF).

        – Maps and charts are always associated with a
        specific epoch. (i.e. NAD83 Cors96 Epoch 2002.0)
        – If differential corrections are applied to any GPS
        measurements, reference frames must be
        considered.

43
     GPS COORDINATES

     EPOCHS

      – ITRF versus NAD83 example in Southern California
        ITRF00 (EPOCH:2006.0325)




                                   Meters




                                      NAD_83(CORS96)(EPOCH:2002.0000)




44
     GPS SOLUTIONS


       Autonomous
         – Single receiver solution (regardless of type).
           0 – 10 meter variable accuracy.

       DGPS
         – Differential “Code” solution. 1 – 3 meters of accuracy.

       CPD Float
         – Carrier Phase Differential Float solution. 10 cm to 1 m
           accuracy.

       CPD Fixed
         – Carrier Phase Differential Fixed solution. 1 – 2 cm
           accuracy. Survey grade.

45
     GPS SURVEYING METHODS


       Post-Processed
         – Static: Stationary on point for extended periods of time.
         – Rapid Static: Stationary on point for typical occupation
           times of 3 to 20 minutes.
         – Kinematic: Stationary initialization, then dynamic data
           collection.

       Real-Time
         – DGPS: Code solutions suitable for most mapping and
           GIS applications. RTCM correction is typical.
         – Real-Time Kinematic: DGPS code and carrier solution
           capable of producing centimetric results.


46
     TYPES OF SURVEYS

          Control Surveys
           – Accuracy requirement: 0.5–3 cm (0.015 – 0.08 ft), 3-D


          Topographic Mapping
           – Accuracy requirement: 1-20 cm (0.03 – 0.5 ft), 3-D


          Boundary Surveying
           – Accuracy requirement: 1–3 cm (0.03 – 0.1 ft), 2-D


          Stakeout
           – Accuracy requirement: 1–3 cm (0.03 – 0.1 ft), 3-D



47
     CONTROL SURVEYS


       Precise, permanent points
         – Will be the basis of other, less accurate surveys

         – Monuments must be physically stable

         – Tripods used (or pillars)

         – Calibrated level vial

         – Antenna phase center modeled



48
     TOPOGRAPHIC & BOUNDARY SURVEYS

        Topographic Mapping
         – Measure existing physical object on the ground
         – Linking physical objects to “attributes”
         – As-Builts verifying position and content



        Boundary Surveying
         – New monumentation
         – Retracement of previous surveys




49
     STAKEOUT

     •   Accuracy requirements vary

     •   Points are monumented in real-time

     •   QC is critical. Blunders can be expensive

     •   Reporting

         – Cut-sheets

         – Lath marks

         – Pad certifications



50
     GPS KEYWORDS

     •CDMA (Code Division Multiple Access):      A method of frequency sharing
     where many radios can use a single frequency in coordination through
     the use of a code identifier. GPS satellites utilize this technology.

     • Ionosphere:      The band of charged particles between the exosphere
     (50 -250 miles above earth’s surface) which represents a non-
     homogenous and dispersive medium for radio signals.

     • P-Code (Precise or Protected Code):     A lengthy (267 days) code that is
     divided into one-week segments. A segment is then uniquely assigned to
     each satellite and is generally reset each week.

     • SNR (Signal to Noise Ratio):   A measurement of the data content of the
     signal relative to the signal’s noise. A higher number is better.

     • Y-Code:   The encrypted version of the P-Code

51
     GPS RESOURCES

      •   Magellan on the Internet:
          http://products.magellangps.com/en/support/
           – Firmware updates
           – Software updates
           – Reference Manuals
           – Almanacs
           – Antenna Specifications
           – Training Materials
           – Support FTP site link
           – Repair Requests
           – Contact Information



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