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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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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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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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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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• 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

Eric Gakstatter

Contact Information:[email protected]

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