An Introduction to GPS / GNSS

Transcription

1 An Introduction to GPS / GNSS Prepared by: In Partnership with: NSF DUE ; Outline Terms: GNSS & GPS? Why do we use GNSS? What is GNSS? How does GNSS Work? What do you need to know about GNSS? What can you do with GNSS? How is GNSS used in the real world? GNSS and GPS GPS = Global positioning system GPS refers to the constellation of navigation satellites associated with the American System (which is a global system). For a long time, GPS was the only game in town, so everything (satellites, receivers, etc.) was referred to as GPS Times are changing other options (besides GPS) are quickly developing June 1-7, 2013 Introduction to GPS/GNSS Page 1

2 GNSS = Global Navigation Satellite System GNSS is an umbrella term that includes any satellite navigation system. Options include: GPS (U.S. operational since 1994) GLONASS (Russian re operational since 2010) Galileo (European Union anticipated operation:2019) Compass (China Operational in Asia/Pacific since 2012 / anticipated global operation: 2020) Why GNSS? Many features have addresses and landmarks that are associated with a destination. Fred Jones 332 Elm St. Frog Holler, VA Why GNSS? However, there are many features that do not have addresses There are many MAJOR cities that do not even have STREET NAMES! And then there is the open ocean and sky June 1-7, 2013 Introduction to GPS/GNSS Page 2

3 Why GNSS? Location, Location, Location and INFORMATION!!! Pre GPS Navigation is critical Historical Navigational tools have limits: The Sextant doesn t work if it is cloudy Lowrance radionavigation: only worked near land The military had its own reasons for determining location Identify targets Friendly fire issues smart bombs What is GNSS And how does it work? June 1-7, 2013 Introduction to GPS/GNSS Page 3

4 What is GPS? GPS (and GNSS) is not a single UNIT! GPS = Global Positioning SYSTEM GPS was developed by the Department of Defense at a cost of >$12 billion Funding for the GPS was contingent on making the system available to the public. GPS (and GNSS) is a SYSTEM There are three major components in this system: 1. Satellites 2. Ground Control Stations 3. GNSS Receivers (or units) Satellites There are satellites up there at any given time orbiting the earth at ~11,000 naut. miles. The DOD knows the EXACT location of each of the satellites at any given moment. These satellites have VERY accurate clocks on board. The satellites continuously send radio signals towards earth. These radio signals are picked up by GPS receivers. June 1-7, 2013 Introduction to GPS/GNSS Page 4

5 Satellites: A Beehive of Activity GPS Control Stations There are five control stations that monitor the satellites. Control stations enable information on Earth to be transmitted to the satellites (updates and fine turning). Control stations continuously track satellites, and update the positions of each satellite. Without control stations, the accuracy of the system would degrade in a matter of days. GPS Receivers GPS units are referred to as receivers. They receive information (radio signals) from satellites. The GPS receiver knows how long it takes the signal to travel from the satellite to the receiver. June 1-7, 2013 Introduction to GPS/GNSS Page 5

6 GPS Receivers The GPS receiver knows how long it takes the signal to travel from the satellite to the receiver. The Receiver is therefore able to calculate its distance from the satellite. Distance = time x velocity Distance = time x 186,355 mi./sec. The receiver can calculate the time that signal traveled from the satellite to the receiver. The receiver is therefore able to determine its exact distance from the satellite. How GPS (and GNSS) Works One satellite How GPS Works If the GPS receiver only obtains signals from 1 Satellite, then it knows that it is located somewhere on this sphere June 1-7, 2013 Introduction to GPS/GNSS Page 6

7 How GPS Works How GPS Works If the GPS receiver only obtains signals from 2 satellites, then it knows that it is located somewhere where these 2 spheres intersect How GPS Works June 1-7, 2013 Introduction to GPS/GNSS Page 7

8 How GPS Works If the GPS receiver obtains signals from 3 satellites, then it knows that it is located somewhere where these 3 spheres intersect (2 points) How GPS Works How GPS Works A fourth satellite is required to determine the exact location and elevation. June 1-7, 2013 Introduction to GPS/GNSS Page 8

9 What do you need to know about GNSS? Different Grades of GNSS receivers Recreational Grade GNSS Accurate to within 5 meters (could be better, but don t rely on it) Suitable for hunting, recreational, and some business uses Lowest cost (smallest, and easiest to use): ~$100 $800 Mapping Grade GNSS Accurate to within 1 meter (3 feet) Requires differential processing (from a base station) Suitable for many natural resource applications, city planning $800 $7,000 Survey Grade GNSS Accurate to within 1 cm Suitable for building bridges $15,000 $30,000 What you need to know about GNSS? Signal Accuracy Issues Selective Availability Tricks of the Trade Current Applications of GNSS Future applications of GNSS June 1-7, 2013 Introduction to GPS/GNSS Page 9

10 GPS: Signal Accuracy There are 2 types of GPS Signals: P code: ( Precise code) This is only available to the military and some selected public officials. Very precise, not degraded. C code: ( Civilian Code). Less precise Signal can be degraded (by scrambling the signal) especially in times of conflict. This is what the GARMIN receivers (and all public GPS receivers) work with Correcting for errors: Selective Availability It is possible to correct for inherent signal errors. This process is called Differential Correction Here s how it works Differential Correction There are already established base stations established around the U.S. Surveyors have determined the precise location of these base stations. Each base station has a GNSS receiver, which collects incoming (error prone) signals. The true (surveyed) location coordinates are then compared to the GNSS coordinates. The correction values are then: Posted to the web for later correction (post processing); sent to other GNSS receivers in the field (correction on the fly ). June 1-7, 2013 Introduction to GPS/GNSS Page 10

11 Differential Correction Base station w/ GNSS receiver at known location: Differential Correction Signal GNSS receiver in the field collecting points, routes, etc. Exact known (surveyed) coordinates differ from GNSS coordinates at this location = exact amount of error! WAAS The Wide Area Augmentation System (WAAS) is a differential GNSS system that is being constructed to support GNSS accuracy in aircraft. WAAS also provides additional accuracy on the ground The GNSS receivers that we are using are WAAS compatible WAAS Most (but not all) GNSS receivers are WAAS compatible. 95% of GNSS receivers on the market today are WAAS compatible The GARMIN Venture HC is WAAS compatible June 1-7, 2013 Introduction to GPS/GNSS Page 11

12 Other Tricks of the Trade: Averaging Averaging: A GNSS receiver can collect points continuously for seconds. The receiver can then average all these locations together This only works when you are standing still!! Note that not all GNSS receivers have an averaging capability GNSS Collected Points GNSS Averaged Position True location Other Tricks of the Trade: Satellite Distribution It is better for your receiver to get a fix on distributed satellites, then poorly distributed satellites. Positional Dilution of Precision Good Satellite Distribution Poor Satellite Distribution GNSS planning software... June 1-7, 2013 Introduction to GPS/GNSS Page 12

13 GNSS Satellite Visibility: Blacksburg July 12, 2012 Other Tricks of the Trade: MultiPath Errors Try and stay away from buildings and other structures when using a GNSS receiver Satellites may not be visible This can introduce error Other Tricks of the Trade: Tracking Satellites GNSS has worldwide coverage HOWEVER You can lose satellite coverage (or received degraded signals) in areas with dense foliage, in urban canyons, etc. You may also lose satellite coverage (or receive degraded signals) in deep valleys or gorges. June 1-7, 2013 Introduction to GPS/GNSS Page 13

14 Accuracy How accurate is a $150 GNSS? That s the million dollar question How accurate is a $150 GNSS? (It depends ) Acknowledgements: Dr. Phillip Rasmussen, Utah Geospatial Extension Specialist Brand A Day 1 Brand A Day 2 Brand A Day 3 Brand A Day 4 Brand A Day 5 Brand B Day 1 Brand B Day 2 Brand B Day 3 Brand B Day 4 Brand B Day 5 June 1-7, 2013 Introduction to GPS/GNSS Page 14

15 GNSS Data Collection Waypoints Tracks Routes Find/GOTO And more..! What can you do with a GNSS? Collect and store points (positions) These are called WayPoints. Field corners, insect infestation areas, crop damage, individual trees, trail heads, creek crossings, point source pollution, camping sites, and don t forget your car! Download the points onto your computer and integrate them with other mapping programs June 1-7, 2013 Introduction to GPS/GNSS Page 15

16 Waypoints Corner2 Point3 Latitude: Longitude: W Elevation: 2108 feet 001 What can you do with a GNSS? Collect and store the path that you have walked / driven These paths are called TRACKS. Calculate the distance of a track (i.e. perimeter around a field) Calculate AREA measurements within a TRACK (after walking around a field or parking lot...) Save and Download TRACKS onto your computer. Tracks (just start walking ) What June 1-7, 2013 Introduction to GPS/GNSS Page 16

17 Tracks (just start walking ) Each track point has important information associated with it... Virtual bread crumbs Latitude: Longitude: W Elevation: 2108 feet Time: 13:22.15 Date: 05/08/2009 Track points can be collected: Based on a time period (every 10 seconds) Based on distance (every 20 feet) Or a combination of time and distance (every 10 secs. or 20 feet, whichever comes first). Tracks You can track your way back... * You can use the track data to estimate area / perimeter* You can use the time stamp in the trackfile to georeference (or geotag) photographs!* * We ll do this later! What can you do with a GNSS? Collect and store ROUTES Routes are similar to TRACKS, but are created by associating a series of Waypoints Tracks are straight lines... Routes can be handy for measuring square fields and straight lines You can measure the length and area (acreage) of a Route. June 1-7, 2013 Introduction to GPS/GNSS Page 17

18 Routes #3 #2 #1 #4 1. Establish Waypoints at strategic locations 2. The GNSS Receiver Connects the dots 3. Area and perimeter measurements are generated #5 Routes vs. Tracks Yellow lines = Route Red lines = Track Red dots = Track points What can you do with a GNSS? Navigation! The GOTO (or Find ) function Using the GOTO function, the GNSS will guide you to a predefined Waypoint (you choose which one ) using an electronic compass and pointer The GOTO/FIND function is like using Autopilot You can program the GNSS to beep when you are within a certain distance of a selected Waypoint June 1-7, 2013 Introduction to GPS/GNSS Page 18

19 What can you do with a GNSS? Tide Tables Many of the marine GNSS s have built in tide tables. They provide tidal information and ranges for any date and any place The GARMIN Venture HC does not have tide table information Extra bell & whistle = extra $! What can you do with a GNSS? Speed GNSS s calculate your ground speed as you walk, run, drive, or fly What can you do with a GNSS? Elevation In addition to providing you with your latitude and longitude, GNSS provides you with elevation information. Elevation is not as accurate as X,Y information. Some GNSS s have built in barometric altimeters (to increase accuracy of z values). This option costs a bit extra! June 1-7, 2013 Introduction to GPS/GNSS Page 19

20 What can you do with a GNSS? Measure Area / perimeter Farmers can use a GNSS to measure the area of a pasture or a field of corn Natural Resource Agents can measure the area of a proposed conservation easement Educators (and students!) can measure the area of impervious surfaces (or green space) around their campus s and communities... Current Application Areas of GNSS Public Safety Environmental resource management Aviation Military Local planning Surveying Recreation Business The Future of GNSS (is bright) Acknowledgements: Keith Clarke June 1-7, 2013 Introduction to GPS/GNSS Page 20

21 The Future is bright The DoD is in the process of upgrading the existing GNSS satellite constellation better coverage availability (i.e. in forested areas) anticipated greater accuracy (even for the recreational grade GNSS receivers) WAAS Satellites Historically, some areas in Virginia have had trouble acquiring the WAAS satellite A new WAAS satellite was launched in Fall 2006 Better coverage for Virginia = higher accuracy levels The Russian GNSS System Is called GLONASS Has fallen into disrepair. Some new Russian GLONASS satellites are have been launched Impacts: Potentially increased accuracy for US receivers that receive both US and Russian GNSS satellite signals (the private sector follows demand ) Just need to keep our eye on the Russian economy (no $, no satellites!) June 1-7, 2013 Introduction to GPS/GNSS Page 21

22 The European GNSS System Galileo will be Europe s own global navigation satellite system More accurate than the U.S. s current GNSS system (~4 feet) Better coverage area than the U.S. s current GNSS system Compatible and interoperable with the American global positioning system (so we ve been told...) Europeans, Chinese, India, etc. GNSS Receivers Continue to get better and better better antennae, more efficient power consumption, smaller increasingly more bells + whistles (maps, hard drives, cameras, etc.) Inexpensive, but the new bells + whistles keeps prices fairly stable... The applications are endless and keep in mind that there are ~322,000,000 wireless subscribers in the U.S. (that s a market penetration of 101%), as of July Source: June 1-7, 2013 Introduction to GPS/GNSS Page 22

23 GNSS recreational (and educational) uses Geocaching. Geocaching is an entertaining adventure game for GNSS users. The idea is to hunt for objects (prizes) that have been placed in the landscape (virtual orienteering). Pick a prize, and leave a prize but Geocachcing is so passé But have you ever tried Geodashing? In this game, a list of coordinates, selected at random from around the globe, is presented to all users and teams. First one there, wins.. Requirements: somebody with a lot of free time on their hands, a GNSS, Lots of extra batteries, a new pair of sneakers, a passport, frequent flier miles and your dad s VISA Card (or a trust fund will do). Some GNSS Applications are innovative Use GNSS to locate the loo! 29/sat.lav.ap/index.html June 1-7, 2013 Introduction to GPS/GNSS Page 23

24 GNSS based buddy stalkers (oops, I mean buddy tracking) add on service Create a buddy list and locate your pals on your Smartphone. Is your girlfriend really at the library? Other GNSS Data Loggers and Tracking Devices We all know that UPS / FedEx and the major freight haulers use GNSS Other folks are tracking people too! Car Navigation Systems are getting into buddy tracking as well Garmin and TomTom have well established systems in place June 1-7, 2013 Introduction to GPS/GNSS Page 24

25 Car Insurance companies have been eyeing this technology for years GNSS based tracking, routing, and fleet management You ve seen those trucks going down the highway with the little round things on the top... We are not only tracking trucks... Active tracking: real time monitoring... Passive tracking: provides a history.. June 1-7, 2013 Introduction to GPS/GNSS Page 25

26 Example of passive tracking Rocky Knob Economic Development and Tourism Study Tourist Surveys: Linking GNSS with traditional surveys June 1-7, 2013 Introduction to GPS/GNSS Page 26

27 Results 490 visitors contacted over 4 data collection periods (July, August, September, and October). 323 agreed to participate (Response rate of 65.9%) Of these 323 visitors, 312 visitors have returned a survey/gnss unit (Secondary response rate of 96.6%) Table 16. How many hours did you spend planning your trip to Floyd and Patrick Counties? Frequency Percent % % % % % More than % Mean = 1.0 Median = 0.5 SD = 1.5 Tourist surveys Pat. + Floyd Co. GPS Map June 1-7, 2013 Introduction to GPS/GNSS Page 27

28 Site Location: Take into account existing traffic and tourist visitor patterns There s a high correlation between the VDOT traffic count map and the GPS tourist surveys GPS Fights Crime! June 1-7, 2013 Introduction to GPS/GNSS Page 28

29 The Degree Confluence Project The "world's largest distributed expedition project. Goal: to visit each of the latitude and longitude integer degree intersections in the world, and to take pictures at each location. GNSS related careers Agriculture Conservation managers Wildlife technicians Surveying companies Local governments State agencies Federal agencies The military Law enforcement Real estate Software programmers Basically, any profession that requires data collection in the field can benefit from using GNSS. The applications are limited only to your imagination... And evidence of this can be found on the GNSS based applications developed for SmartPhone devices) June 1-7, 2013 Introduction to GPS/GNSS Page 29

30 There s a Variety of Software Products Available to Support GNSS GPS Utility (free) DNR GPS (free) USA PhotoMaps (free) RoboGeo (demo version and $75 version) Terrain Navigator (~$89) Data cards (topos, etc.) and aerial photography subscriptions for your GPS receiver And just think about all of the 1000 s of Smartphone applications (Urbanspoon, etc.) Things to keep in mind... GNSS can serve as an accurate data collection tool for GIS applications; GPS applications are becoming increasingly prevalent in our society, and support a variety of applications; With GNSS receivers, you (more or less) get what you pay for (w/ prices ranging from $20,000 + $59); This technology is CURRENTLY used to support govt. services / private businesses; Smartphone apps. are going to make all of this take off Knowing how to use a GNSS does not make you a surveyor!!! Any Questions? June 1-7, 2013 Introduction to GPS/GNSS Page 30