Nightmare on GIS Street: GNSS Accuracy, Datums, and Geospatial Data
Speaker: Eric GakstatterContributing Editor – GPS World
Editor - Geospatial SolutionsPresented at: Association of Petroleum Surveying & Geomatics
Houston, TXApril 22, 2014
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Agenda
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- What’s the problem and why should I care?
- The challenge of horizontal datums
- The challenge of integrating high-accuracy data into workflows.
- Audience Q&A. Discussion.
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What’s the problem and why should I care?
- The cost of acquiring high-precision geospatial data is declining (eg. GNSS, airborne/terrestrial Lidar, UAVs, etc.)
GNSS technology is going to advance significantly more in the next 5 years than it has in the past 10
years
GNSS is the new GPS
GNSS = Global Navigation Satellite System
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World-Wide GNSS
ACTIVE GNSS:
-GPS (USA)
-GLONASS (Russia)
-SBAS:WAAS (North America), MSAS (Japan)
EGNOS (Europe), Omnistar, Terrastar
-QZSS (Japan)
-RTK Networks
-DGPS/NDGPS
PLANNED GNSS:
-Galileo (Europe)
-BDS (China)
-SBAS: GAGAN (India)
-SBAS: SDCM (Russia)
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• Not only is GNSS receiver technology constantly evolving, so is the GNSS infrastructure (satellites, signals and control).
• This is one of the reasons that the GNSS industry is so dynamic and will be for the foreseeable future.
• These changes will affect the way that GNSS mapping and surveying users perform their work.
GNSS is Changing
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GPS Constellation Status
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• There are currently 31 operational GPS satellites.
• 20 x GPS Block IIA/IIR. L1 C/A, L1/L2 P(Y)
• 7 x GPS Block IIR-M. L1 C/A, L1/L2 P(Y), L2C
• 4 x GPS Block II-F. L1 C/A, L1/L2 P(Y), L2C, L5
• L2C = More robust iono correction for high precision positioning. No need for cross-correlation (semi-codeless).
• L5 = Similar to L2C, but stronger signal @ 1176• Civil signals (black, red), Military signals (blue)
•
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GLONASS
Russia’s Satellite Navigation System
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• Declared fully operational in December 2011.
• 24 operational satellites. Most since 1997.
• A valuable augmentation to GPS. Not used as a stand-alone system yet.
• Valuable to high-precision users (RTK, sub-meter) because it increases productivity.
• 5-10 satellites are added when using GLONASS.
• Increases productivity, not accuracy.
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Galileo
Europe’s Satellite Navigation System
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• First launch of operational Galileo satellites (2) occurred in 2011. Two more Galileo satellites were launched Oct. 12, 2012.
• Production launches scheduled for Summer 2014. Launched in pairs.
• Constellation of 18 Galileo satellites projected for 2015/2016 timeframe.
• Highly compatible with GPS L1/L5.
• No L2 support.
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BDS
China’s Satellite Navigation System
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• More high-precision GNSS receivers are sold in China than the rest of the world combined.
• BDS is currently a regional system of satellites orbiting in a figure eight pattern above China that add ~14 satellites on top of GPS and GLONASS.
• The RTK environment in China is better than any other place in the world due to the significant number of satellites in view.
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• GPS+Galileo = 20 average satellites in view.
• Add 30 more from BDS and 24 from GLONASS.
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SBAS
Satellite-Based Augmentation System
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• SBAS – WAAS/EGNOS/MSAS/GAGAN. Free source of GPS L1 corrections.
• SBAS was designed for aviation, but used widely by geospatial professionals as an accurate source of GPS L1 corrections.
• SBAS was designed primarily for integrity, but can be optimized for accuracy to achieve sub-meter precision.
Public SBAS (sub-meter)
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• Commercial PPP SBAS (decimeter world-wide subscription services):
- Starfire
- OmniSTAR
- Terrastar
• Public PPP SBAS (free decimeter world-wide service):
• IGS RT <rt.igs.org>
PPP SBAS (decimeter)
OmniStar/Starfire/Terrastar
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• Commercial RTK Networks• - Surveying equipment dealers
• - GNSS eq. manufacturers – Trimble/Leica/Topcon
• Commercial RTK Clusters• - Agriculture
• Public RTK Networks• - State agencies (eg. Dept of Transportation)
• Public RTK Clusters• - Plate Boundary Observatory (PBO)
RTK
PBO RTK Bases
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• OmniStar – ITRF08 current day epoch
• WAAS – ITRF08 current year epoch
• DOT RTK Networks – NAD83/2011 2010.0
• NGS CORS streaming (discontinued) – ITRF00 1997.0
• PBO RTK bases - ???
• Commercial RTK Networks (surveying) - ??? Localize?
• Commercial RTK Clusters (ag) – WGS-84??
Disparate Datums
Public RTK Base Stations in the U.S.
Two recent examples of using Public RTK bases:
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Public RTK Base Stations in the U.S.
Case #1. Colorado.
-Windows Mobile data collector w/AT&T SIM card for internet connectivity
-~12 mile baseline
-Accuracy: 1.9cm horizontal RMS. Adjusted from ITRF00 1997.0 to NAD83.2011 2010.0 using HTDP
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Public RTK Base Stations in the U.S.
Case #2. California (SF Bay Area)
-Samsung Note smartphone (Android) running AutoCAD 360.
-~5 mile baseline, 0.75” precision
- Accuracy: ????
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Trending towards real-time decimeter (PPP) and centimeter positioning (RTK)
Never in history has real-time, high-precision technology been so available and affordable.
And we’re only just beginning…………………….
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Trend
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GNSS L5 Signal
The Beginning of a New Era
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• May 2010 marked a new era of GPS with the launch of the first GPS satellite equipped to broadcast an L5 carrier.
• According to the U.S. Gov’t, a full constellation of 24 GPS satellites broadcasting L5 (and all legacy signals) will be in orbit by 2020.
• Europe’s Galileo could accelerate a full L5 constellation (18) as soon as 2015/2016.
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• L5 = broadcast signal four times more powerful than L2C, frequency further separated from L1 which enhances mitigating the effect of the ionosphere.
• L5 designed for safety-of-life apps (eg. aviation) and frequency (1176.45 MHz) is in the highly protected aeronautical navigation band.
• GPS, Galileo and BDS support L5.
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When will L5 be available?
• GPS won’t have a full constellation of satellites broadcasting L1/L5 until 2020.
• Galileo could accelerate that by five years if the EU and US keep their projected schedules.
• If GPS has 12 satellites broadcasting L1/L5 by 2015 and Galileo has 18 satellites broadcasting L1/L5 by 2015, there would essentially be a full constellation of satellites broadcasting L1/L5 signals.
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Significant developments
• SBAS (WAAS, EGNOS, MSAS) became operational. GAGAN and SDCM conceived.
• GLONASS matured.
• RTK Network proliferation.
• PPP real-time decimeter services matured (Starfire, OmniSTAR, Terrastar).
• L2C introduced.
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High-Precision GNSS Technology
The Next 5 Years
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The Next 5 Years
• Complete hybrid L5 constellation (GPS/Galileo/BDS).
• Cheaper/more accurate GNSS receivers.
• Initial deployment of Europe’s Galileo and Chinese BDS.
• Continued proliferation of RTK Networks.
• Further refinement of PPP real-time services (eg. Trimble RTX, IGS-RT).
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• The new GPS L5 signal will result in very low-cost L1/L5 receivers capable of cm-level horizontal/vertical precision.
• High-precision GPS receivers trending towards commoditization.
• RTK on your mobile phone by 2020?
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• GNSS performance around obstructions such as tree canopy, buildings, terrain blockage.
• Geodesy – datums, coordinate velocities. The “Nightmare on GIS Street”. Combining disparate data sets.
• Communication for real-time GNSS corrections.
Three Gotchas
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• Knowing what you have (metadata).
• Having tools to transform accurately between datums.
• Knowing when to transform between datums.
• Handling velocities.
The Nightmare
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Velocities
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• Don’t know what you have.
• Simplicity vs. accuracy. Geospatial software operators follow the path of least resistance.
• Transformation workflows are not simple or understandable.
• Velocities are a difficult concept for the average geospatial specialist.
• Mainstream workflows to deal with velocity models are largely non-existent.
• Velocity models are a work in progress.
Why is it so Complex?
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• Large water utility company
- getting past the infatuation with imagery.
- finding imagery metadata. NAD83/86, 91, 96, 2011?
- Fixing incorrect assumptions on metadata for different data layers.
- Collecting high-precision GNSS data. Some from WAAS (ITRF08 current year epoch), some from commercial RTK network (NAD83/2011 2010.0) using the same receiver and software.
Case #1 - Challenges
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• Consortium of large utility companies
- Setting standards and developing a common workflow.
- Geographic coverage area is CONUS (lower 48).
- GNSS technology selection. Real-time PPP SBAS selected, largely driven by ubiquitous national coverage and common datum.
- Workflow was unable to deal with a real-time ITRF -> NAD83/2011 transformation.
- Ultimately, real-time PPP SBAS was the incorrect technology for many of the projects.
Case #2 - Challenges
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• The ability to collect high-accuracy geospatial data is cheaper and easier than ever before.
• Stewards of geospatial data are largely ill-equipped to accurately deal with disparate data sets.
• Geospatial workflows are largely ill-equipped to accurately deal with disparate data sets.
• Velocities are a foreign concept to most geospatial data stewards.
• Velocity models are a work in progress.
Takeaways
Comments?
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Questions?
Eric Gakstatter
Contact Information:[email protected]
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