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Similar to Global Navigation Satellite System ( GNSS ) refers to any satellite constellation that provides global positioning
Global Navigation Satellite System ( GNSS ) refers to any satellite constellation that provides global positioning
- 1. DGNSS Compiled by Ir. MUVUNYIGermain Msc .Geo-informatics
- 2. Differential GNSS (DGNSS)Technique • P o s i t i o n i n g of a user can be done with the help of a DGNSS station. • The DGNSS station knows its actual position and computes its estimated position from signals from the navigation satellites. From the two positions, the error correction is sent to the user who will correct its estimated position from signals from the navigation satellite with the error correction as shown in the figure , With the correction signal, the new computed position is more accurate. • Finally, singledifference, double difference and triple difference for code measurements and carrier phase measurements may help in specific areas/scenarios too
- 3. Exact known (surveyed) coordinatesdiffer from GNSS coordinates at this location = exact amount of error! GNSS receiver in the field collecting points, routes, etc. Differential Correction Signal Base station w/ GNSS receiver at known location: Differential correction
- 4. Satellite‐Based Augmentation System(SBAS) Technique • The technique in satellite based ‐ augmentation system (SBAS) is similar to DGNSS, except that the ground DGNSS station is replaced by GEO satellites .
- 5. • Satellite-Based AugmentationSystem (SBAS) is suitable for applications where the cost of installing a base station is not justified, or if the rover stations are spread over too wide of an area • SBAS is a geosynchronous satellite system that provides services to improve the overall GNSS accuracy • Improve accuracy through wide-area corrections for range errors • Enhance integrity through integrity monitoring data • Improve signal availability if SBAS transmits ranging signals from it satellites 01/17/2025 5 Satellite-Based Augmentation System
- 6. Real-Time Kinematic –RTK •RTK (Real-Time Kinematic) – a proven method of positioning in real- time at the cm-level. Invented in the early 1990’s. • RTK makes GPS/GNSS a very efficient tool for some tasks such as construction staking, machine control, topographic surveys and many others where precise real-time positioning is valuable. • RTK has been supported by The growing of CORS (Continually Operating Reference Station) concept . • Traditional RTK is a single-baseline solution between a base station and a rover unit.
- 7. • The rangeis calculated by determining the number of carrier cycles between the satellite and the rover station, then multiplying this number by the carrier wavelength • RTK corrections from a base station is transmitted to the rover to correct for errors such as satellite clock and ephemerides, and ionospheric and tropospheric errors • A process called “ambiguity resolution” is used to determine the number of whole cycles • Similar to Differential GNSS, the rover’s position accuracy will depend on the base station’s accuracy, baseline length, and the quality of the base station’s satellite observations • Virtual Reference Stations (VRS) is a form of Network RTK where there is a wide network of base stations sending out corrections to user stations on demand 01/17/2025 7 Real-Time Kinematic (RTK)
- 9. RTK Clusters • AnRTK Cluster is a group of strategically spaced reference stations designed to provide single-baseline RTK coverage within a certain area. • All of the reference stations in the Cluster are managed by a single entity. • The reference stations in the Cluster are typically owned by the managing entity and/or by cooperative partners who want to utilize the Cluster. • The user must select which reference station in the Cluster they wish to use. This is typically the reference station closest to the user to minimize distance-dependent errors. • RTK Networks originated from RTK Clusters.
- 10. RTK Clusters • Benefitsof RTK clusters over traditional RTK: 1. Assumes responsibility of running a reference station from the user. 2. Increases efficiency. The user turns on their receiver and begins work almost immediately. 3. Significantly reduces the capital equipment cost of implementing high precision GPS especially when field work is spread out over a wide area.
- 11. RTK Networks EarlyRTK Networks began to appear around 2003. Outwardly, they appear similar to RTK Clusters. However, they are significantly different in several ways: 1. They provide a network RTK correction based on most or all of the reference stations in the network. 2. The density of reference stations in an RTK Network is 3-6 times less than an RTK Cluster. Example, covering 3 million acres with an RTK Cluster may take 30 reference stations while an RTK Network may only require 5. 3. RTK Network (software) largely mitigates distant-dependent variables such as the ionosphere, troposphere and orbit errors. 4. RTK Network infrastructure (hardware and software) is much more complex than an RTK Cluster. Reference station data is processed by one or more central servers before being distributed to users.
- 12. RTK Networks Critical componentsfor successful RTK operations: • RTK-capable GPS/GNSS receiver • Lots of satellite observables. • Solid, reliable communication between base and rover
- 13. Single Baseline RTK 10-20km radius Single RTK Base Single RTK Rover
- 14. Issues with SingleBaseline RTK Overhead: Must own, setup and survey base station Availability: Single point of failure Reliability: No redundancy (i.e. multiple determination) Accuracy: Limited range (10-20 km) and baseline dependent Initialization/Re-initialization: Seconds to minutes Security: Must attend temporary base station Productivity/Efficiency: Low (see all of the above) Flexibility: Mixing of receivers/antennas problematic The solution is RTK network
- 15. Virtual Reference Station(VRS) Technique • The virtual reference station (VRS) technique is a type of Network RTK. • In the VRS concept, there are a number of GNSS reference stations connected to a control center via data links. • Information is collected at the control center from all GNSS reference stations and corrections are generated at the control center. The key idea is to generate a VRS nearby the user and together with the raw data, an accurate positioning can be obtained. • First, the user sends its rough position to the control center via GSM/GPRS/3G/4G. Then, the control center sends corrections to the user and the user calculates a good quality DGNSS solution and updates its new position. The user then sends its new position to the control center and new corrections are sent to the user who recalculates a more accurate position.
- 19. Wide Area AugmentationSystem (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
- 20. How does WAASsystem work? • GNSS receiver receives a signals from at least 4 GNSS satellites, and calculates the position • At the same time, a WAAS ground station (hopefully nearby) receives signals from GNSS satellites, and calculates the position of the ground station for that particular second in time (remember, that satellites are constantly on the move, and there are other factors that will influence the accuracy of GNSS signals at any given point in time...) • The WAAS ground station compares the GNSS derived position, with it’s exact (surveyed) location. It then calculates a correction. This correction is transmitted to the WAAS satellite. • The WAAS satellite then sends the correction information down to your GNSS receiver. Your GNSS receiver corrects the coordinate locations derived from the GNSS satellite constellation (based on the WAAS correction information). This is all transparent to the user, and happens “on the fly”. • The final product should be a more accurate GNSS locational calculation! • Note that a WAAS satellite must be “visible” (not physically visible, but your GNSS receiver must be in communication with the WAAS satellite) in order for all of this to work...!
- 21. WAAS Most (but notall) GNSS receivers are WAAS compatible. 95% of GNSS receivers on the market today are WAAS compatible The GARMIN Venture HC is WAAS compatible
- 22. How accurate isa $150 GNSS? (n Acknowledgements: Dr. Phillip Rasmussen, Utah Geospatial Extension Specialist
- 23. • Collect andstore 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 GNSS applications
- 24. Waypoints 001 Corner2 Point3 Latitude: 37° 16’18” Longitude: W80° 28’ 45” Elevation: 2108 feet
- 25. • Collect andstore 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. GNSS applications
- 26.
- 27. Tracks (just start walking…) Latitude:37° 16’ 18” Longitude: W80° 28’ 45” Elevation: 2108 feet Time: 13:22.15 Date: 05/08/2009 Each track point has important information associated with it... “Virtual bread crumbs” 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).
- 28. • 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! GNSS applications
- 29. • Collect andstore 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. GNSS applications
- 30. 1. Establish Waypointsat strategic locations 2. The GNSS Receiver “Connects the dots” 3. Area and perimeter measurements are generated #4 #2 #5 #3 #1 GNSS applications
- 31. Route GNSS applications s vs.Tracks Yellow lines = Route Red lines = Track Red dots = Track points
- 32. 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 GNSS applications
- 33. • 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 $! GNSS applications
- 34. • Speed GNSS’s calculateyour ground speed as you walk, run, drive, or fly GNSS applications hat can you do with a GNSS?
- 35. What can youdo with a GNSS? GNSS applications • 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!
- 36. • 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... GNSS applications
Editor's Notes
- #3 This is an illustration that shows how Differential Correction works. Farmers out west use differential correction so that they can manage their fields in a more efficient manner (precision agriculture). As a side note, almost every French fry that you consume is a product of precision agriculture! The airline industry uses differential correction both on the ground and in the air to support airline safety. Local, state, and federal government agencies use differential correction to improve mapping and inventory efforts. And researchers use differential correction as well. Base stations are most often not ‘towers’. They are often located on the roof of buildings. They may appear like radio antennae.
- #21 WAAS satellites are different satellites from the GNSS satellites. This is how the WAAS system works: You GNSS receiver receives a signals from at least 4 GNSS satellites, and calculates your position At the same time, a WAAS ground station (hopefully nearby) receives signals from GNSS satellites, and calculates the position of the ground station for that particular second in time (remember, that satellites are constantly on the move, and there are other factors that will influence the accuracy of GNSS signals at any given point in time...) The WAAS ground station compares the GNSS derived position, with it’s exact (surveyed) location. It then calculates a correction. This correction is transmitted to the WAAS satellite. The WAAS satellite then sends the correction information down to your GNSS receiver. Your GNSS receiver corrects the coordinate locations derived from the GNSS satellite constellation (based on the WAAS correction information). This is all transparent to the user, and happens “on the fly”. The final product should be a more accurate GNSS locational calculation! Note that a WAAS satellite must be “visible” (not physically visible, but your GNSS receiver must be in communication with the WAAS satellite) in order for all of this to work...!
- #22 This is a good reference when working with accuracy issues
- #24 Waypoints can be considered to be “virtual flags”. Each waypoint has a name associated with it (by default, names are usually 001, 002, etc), a lat./ long. coordinate system, a time/date stamp, elevation, and other information. Customized interfaces (pull down menus, radio buttons, etc) can be developed on tablets, pocket PC’s, smartphone devices, etc. to support efficient data collection.
- #26 This is what a Track looks like. It would, for example, be difficult to calculate the area of this field if you did not have a GIS or other mapping application. With a GNSS, you can calculate the area “on the fly” by walking around it. Question #1: Why would a farmer want to know the area of a field? Question #2: Why would someone want to know the area of a parking lot? If you had this information, how could it support decision making? The little red box denotes an area that we’ll zoom into in the next slide.
- #27 A track is actually comprised of individual “track points” (not a line). You can think of a track point as virtual bread crumbs that are “dropped” as you walk, run, or drive. You do need to be sure that the “track log” is turned on in your GNSS receiver. If not, then your GNSS will not collect any track points. Each track point contains an array of information associated with it, including: Lat./Long. Elevation Time Date
- #28 Tracks are very powerful. We’ll get into some of the uses and applications of GNSS derived track data later!
- #29 People often get routes and tracks confused. Routes are similar to tracks, but they are created by connecting a series of EXISTING waypoints. Thus, if you have not collected any waypoints, you can not define a route! Routes are straight lines, tracks can be very curvy and defined. You can determine length and area from a route. Question #1: Can you think of a situation when collecting area / perimeter information from a route might be more efficient than from a track?
- #30 This is what a route might look like. After the waypoints have been collected, you can then generate differerent scenarios based on the waypoints. Once the waypoints have been collected, these scenarios can be generated back in the office.
- #31 This is how a route looks in comparison to a track. Notice that routes are much straighter than tracks....
- #32 The “GOTO” function will guide you to a predefined waypoint. This is how car navigation systems work. Keep in mind, though, that car navigation systems lead you to a user-defined destination based on a road network that is loaded into the car navigation system. The lower-end recreational grade GNSS systems do not have road a comprehesive road network databased installed, so they can not be used for car navigation...
- #33 Different GNSS receivers have different bells and whistles / functions and capabilities.
- #34 All GNSS receivers will provide you with your speed.
- #35 As long as your GNSS receiver receives signals from at least 4 satellites, it can provide elevation information. Note that the elevation information is typically not as accurate as the lat./long. Coordinate information.
- #36 We’ve already discussed this!