Applications, Products and Services of GPS Technology

Transcription

1 Applications, Products and Services of GPS Technology Enrico C. Paringit. Dr. Eng. University of the Philippines Training Center for Applied Geodesy and Photogrammetry 1

2 Outline of this Presentation GPS Positioning vs. GPS Navigation Applications of GPS Technology Survey Coordinates Time Series GPS Data Products of GPS Technology Receiver Services related to use of the GPS WAAS IGS 2

3 GPS Surveying vs. GPS Navigation (1) According to "when", "where" and "how" the GPS technology is applied. According to operational aspects According to the type of measurement made and the GPS instrumentation used. According to the mathematical models used. 3

4 GPS Surveying vs. GPS Navigation (2) Aspect Surveying Navigation Points coordinated stationary in motio GPS data collection Mode of operation Measured codes Application associated "observation session". Relative positioning high accuracies. L-band carrier wave, hence requiring special instrumentation and software. traditional surveying and mapping functions for an "instant", and the solution is obtained in real-time. Absolute and relative positioning lower accuracies PRN codes defining safe passage of ships and aircraft. 4

5 Application: GPS Position Measurement Systems Land Survey A GPS land survey position measurement system usually incorporates three major components: integrated GPS receiver unit rugged data collector Data collection software Commercial products available. 5

6 Application: GPS Position Measurement Systems GPS-based Mapping and GIS Systems are today's most exciting GPS applications Commercial Integrated highperformance GPS receiver and antenna Up to 2-to-5 meter accuracy. Commercial software available for planning GPS mapping, differentially processing GPS data, GIS output, plotting, and data dictionary creation. 6

7 Applications: Fleet Tracking Real time GPS tracking technology is generally used for dispatching, or when vehicles are located in other areas or in other branches, cities or states, and need to be tracked Uses the internet from various locations. A Passive tracking system may also be used for route verification 7

8 Position Time Series Plot The time series plot shows the GPS station s change in position over time. X-axis: Date of the measurement In 10ths of year or months Y-axis: North (N/S) East (E/W) Height (up/down) (sometimes called Vertical) In millimeters 8

9 GPS Positioning Modes In terms of autonomy ABSOLUTE or POINT positioning: coordinates are in relation to a well-defined global reference system. DIFFERENTIAL or RELATIVE positioning: coordinates are in relation to some other fixed point. In GPS surveying this is referred to as baseline determination. In terms of observer movement STATIC positioning: coordination of stationary points, either in absolute or relative mode. This is generally synonymous with the SURVEYING mode of positioning, based on the analysis of carrier phase observations. KINEMATIC positioning: coordination of moving points, either in absolute or relative mode. This is generally the NAVIGATION mode of positioning, based on pseudo-range observations. 9

10 Classification of GPS Observation According to: Application: Professional vs. Recreational Availability of position: Real Time vs. Postprocessed Type of GPS receiver used: Hand-held vs. Geodetic) Positioning technique: Absolute vs. Relative Observation frequency and period; Continuous vs. Campaign Monitoring 10

11 GPS Observation Method: 1. Continuous stations are continuously-operating longterm or permanent GNSS station installations involving immobile monumentation and sustainable power, and often involving data telemetry. The can be used as pre-existing base stations in campaign surveys (static, rapid static, and kinematic). 2. Static surveys are regional, sub-cm precision with portable equipment and are the standard campaign data collection method 1. typically involve occupying each point for several days to get the highest possible accuracy. 2. Collect at least 6 hours of simultaneous data per day for processing and repeat benchmark occupations if possible. 11

12 GPS Observation Method: Rapid static surveys are static surveys with just enough survey time at each point to be able to resolve the carrier phase integer ambiguity. Rule-of-thumb: collect data for a minimum of 10 minutes per point, and add one minute of occupation time per kilometer of baseline length over 10 kilometers Ex. 8km baseline collect at least 10 minutes of data, and on a 28-kilometer baseline collect at least 28 minutes of data. 12

13 GPS Observation Method: Kinematic surveys are local surveys (<10 km) using mobile GNSS equipment for the purpose of mapping features or of measuring point locations where several cm of precision is sufficient. At least two receiver set-ups are required: a base (stationary) unit and one or more rover (mobile)units. Rely on continuous tracking to resolve the integer ambiguity; while the rover receiver/antenna may be moving during the surveys, continuous lock on the satellite signals must be maintained. Since the data processing software is able to both resolve the ambiguity and track the antenna motion, fixed-integer solutions are obtained nearly instantaneously. 13

14 Kinematic GPS: Observation Modes 1. Post-processing kinematic (PPK) refers to surveys without communication between the base and rover receivers. Processing the data after data collection is required. No navigational capabilities in PPK surveys. 2. Real-time kinematic (RTK) refers to surveys in which the base and rover receivers communicate corrections in real-time via a radio link. Requires additional hardware (base and rover radios) and additional power Limits the survey to an area of several km Eliminates the need for data processing and enables navigational capabilities. 14

15 GPS Survey Method According to Period of Observation 15

16 Applications: Geodetic Surveys 16

17 The GPS-based Geodetic Network = PRS92 Established 300 GPS stations 24 common stations were tied to the old (Luzon) Geodetic Network. Figure shows the shifts which indicate a radial pattern in the errors from the Balanacan datum point. No stations located in Mindanao were used 17

18 Application: Deformation monitoring in the Philippines (1) Galgana, et al.,

19 Deformation monitoring in the Philippines (3) Microplate map of Luzon. Seven blocks were initially assigned to comprise Luzon, designated as the following: Central Luzon (CLUZ), Southwestern Luzon 1 and 2 (SWL1, SWL2), Northwestern Luzon or Ilocos (ILOC), Northeastern Luzon or Cagayan 1 (CAG1), Cagayan 2 (CAG2), and Southeastern Luzon or Bicol (BBLK). Mindoro (MIND) and Central Visayas (CENV) were added as adjoining southern blocks, while Eurasia (EURA), Sundaland (SUND), Observed (arrows with 95% confidence ellipses) and predicted (arrows with no ellipses) GPS-observed site velocities 19

20 Animation: Modeling the Past and Future + 3 million years Now Press space bar to start animation. Source: -3 million years ago 20

21 GPS Products: Receivers 21

22 Classification of GPS Receivers According to Application Receiver Class Used Signal Applications Accuracy Costs Navigation Geodetic Code or phasesmootd code; 1 frequency Code and phase; in general 2 frequencies Car navigation, location-based services, mass market Surveying, geodesy, geodynamics 1 to 10m 5 to 100euros to 0.1m 10,000 to 30,000euros Source: FIG Publication No

23 GPS Services Base GPS services US: Continuously Operating Reference Stations (CORS) Philippine Active Geodetic Network (PAGENet) GPS data enhancement services Product Development Accuracy augmentation (WAAS) 23

24 WAAS: How it works The GPS information collected by the WRS sites is forwarded to the WAAS Master Station (WMS) via a terrestrial communications network. At the WMS, the WAAS augmentation messages are generated. These messages contain information that allows GPS receivers to remove errors in the GPS signal, allowing for a significant increase in location accuracy and reliability. 24

25 WAAS: How it works The navigation payloads broadcast the augmentation messages on a GPS-like signal. The GPS/WAAS receiver processes the WAAS augmentation message as part of estimating position. The GPS-like signal from the navigation transponder can also be used by the receiver as an additional source for calculation of the user s position. 25

26 The augmentation messages are sent from the WMS to uplink stations to be transmitted to navigation payloads on Geostationary communications satellites. WAAS: How it works 26

27 WAAS: How it works The navigation payloads broadcast the augmentation messages on a GPS-like signal. The GPS/WAAS receiver processes the WAAS augmentation message as part of estimating position. The GPS-like signal from the navigation transponder can also be used by the receiver as an additional source for calculation of the user s position. 27

28 Earth Dynamics and Positioning The Earth is constantly changing shape. To be understood in context, when the motion of the Earth's crust is observed, it must be referenced. A Terrestrial Reference frame provides a set of coordinates of some points located on the Earth's surface. can be used to measure plate tectonics, regional subsidence or loading and/or used to represent the Earth when measuring its rotation in space. This rotation is measured with respect to a frame tied to stellar objects, called a celestial reference frame. The International Earth Rotation and Reference Systems Service (IERS) was created in 1988 to establish and maintain the ff: Celestial Reference Frame, the ICRF, International Terrestrial Reference Frame, the ITRF. The Earth Orientation Parameters (EOPs) connect these two frames together. These frames provide a common reference to compare observations and results from different locations. 28

29 Earth Dynamics and Positioning Four main geodetic techniques are used to compute accurate coordinates: the GPS, VLBI, SLR, and DORIS Since the tracking network equipped with the instruments of those techniques is evolving and the period of data available increases with time, the ITRF is constantly being updated. 12 realizations of the ITRS were set up from The latest is the ITRF2008. All these realizations include station positions and velocities. Used tomodel secular Earth s crust changes and compared observations from different epochs (i.e. specific date & time). All the higher frequencies of the station displacements can be accessed with the IERS conventions Continuity between the realizations has been ensured as much as possible when adopting conventions for ITRF definitions. The transformation parameters. relationship linking all these solutions is of utmost importance. They are supplied here by the 29

30 International GNSS Services (IGS) IGS of satellite tracking stations, Data Centers, and Analysis Centers puts GPS data and data products online in near real time to meet the objectives of a wide range of scientific and engineering applications and studies highly accurate geodetic measurements to support numerous scientific fields such as Geodesy ( Geodynamics Engineering Oceanic and atmospheric research, navigation, and; Surveying and mapping 30

31 IGS Products (1) GPS satellite ephemerides GLONASS satellite ephemerides Earth rotation parameters IGS tracking station coordinates and velocities GPS satellite and IGS tracking station clock information Zenith tropospheric path delay estimates Global ionospheric map 31

32 IGS Products (2) 32

33 IGS Products (3) GPS Satellite Ephemerides GPS Satelite Clocks Atmospheric Products GLONASS Satellite Ephemerides 33

34 IGS Reference Frame Stations (1) This set of stations has been selected by the IGS Reference Frame Working Group (RFWG) for the IGS realization of the International Terrestrial Reference Frame (ITRF) The main selection criteria were station performance, track record, monumentation, collocation and geographical distribution. At every update of the RF realization, the number of stations selected has increased, in order to improve the overall quality of the RF realization, and thus all the IGS products that depend on it 34

35 IGS Reference Frame Stations (2) Courtesy: IGS 35

36 ITRF Velocity Fields 36

37 Myths and Facts about GPS It can work indoors GPS signals while relying on CDMA coding technology, does not penetrate well into structures and canopies. It can work on all weather conditions Although signals can be obtained enough to compute for a position, ionospheric conditions affect quality hence accuracy of signal It can work any time of the day There are certain periods where the geometry of the satellites favor good observation. I can be tracked down using GPS in my mobile phone While there are some GPS receivers which have the capability to broadcast your position, the vast majority of GPS devices can only receive information from satellites and cannot broadcast any information. 37