GPS and Geodetic News You Can Use David Conner Geodetic Advisor to the State of Ohio National Geodetic Survey, NOAA 2008 Ohio GIS Conference September 10-12, 2008 Crowne Plaza North Hotel Columbus, Ohio

TOPICS Overview National Readjustment - NAD83 (NSRS2007) GPS CORS, OPUS, OPUS-DB, and more County Scorecard

The CEAO Board, on Sept 6, 2007, passed a resolution to “Adopt NAD83 (NSRS2007) as the reference system of choice for the development of county coordinate systems” in Ohio. National Readjustment NAD83 (NSRS2007) NGS has just completed a major Readjustment to the National Spatial Reference System (NSRS). Updated all GPS survey control point positions in North America. Resolved coordinate inconsistencies between CORS and monumented control New accuracy Standards for Geodetic Control will be implemented

Shifts in Ohio NAD 83 (1995) vs NAD 83 (NSRS2007) Horz Shift Average : m (Max: m) Vert Shift Average : m (Max: m) Example actual horizontal shifts at station SMITH (JY0742) NAD 27 vs NAD 83 (1986)~ 13 meters NAD 83 (1986) vs NAD 83 (1995)~ 20 cm NAD 83 (1995) vs NAD 83 (NSRS2007)~ 1.5 cm

For Stations not Included In the NSRS (2007) readjustment NGS recommends that NAD 83 data that is not part of the NSRS readjustment be readjusted using original observation data Because of the relatively small shifts involved transformation software such as NADCON will not be developed for NAD 83(NSRS2007) NADCON accuracy~ 6 cm (0.2 ft) NAD 83 (NSRS2007) avg shift~ 2.5 cm NGS will streamline the process of project acceptance OPUS DB – coming soon - ?

Ohio’s GPS CORS Network Brought to you courtesy of the ODOT, Bureau of Aerial Engineering VRS/ CORS information Telephone: , or

CORS/OPUS: Overview & Status The CORS network contains about 1,250 GPS tracking stations, and it is growing by about 200 stations per year. OPUS is a Web-based service enabling users to automatically post-process GPS data. CORS = Continuously Operating Reference Station

Vertical standard error achievable when a user submits 15 minutes of GPS data to OPUS-RS

OPUS FLAVORS Try it … Proxy/oraOpusDbWeb /

OPUS-DB

OPUS-DB Sample Datasheet

OPUS  Datasheet Concept

GPS data requirements “OPUSable” 4+ hours of dual frequency data NGS-calibrated antenna OPUS must achieve: ≥ 70% observations used ≥ 70% ambiguities fixed ≤ 0.04m peak-to-peak horizontal ≤ 0.08m peak-to-peak vertical ≤ 0.03m RMS NGS-modeled antenna GPS data (4+hr, good stats )

* optional for “existing” stations. control station description * control station photo * metadata requirements observation notes Simplified bluebooking antenna type, height

NOAA has a relatively new performance metric that assesses how well we are doing at “enabling” local capacity for accurate positioning. This metric:  Makes use of NOAA’s Online Positioning User Service (OPUS) as a proxy to assess the local use of NOAA positioning tools and services. Was developed over the past several years in partnership with National Association of County Surveyors (NACS).  Involves the use of a web-based county scorecard of 23 survey questions specifically focusing on infrastructure, NGS models and tools, NGS capacity building and outreach, and overall satisfaction. We need input from YOU, our core customers, to help NOAA improve its geospatial products and services. For more information, visit or contact:  Your NOAA State Geodetic Advisor, in Ohio (for current list of all Advisors visit OR  Brett Howe We want YOU to tell us how we’re doing NOAA’S County Scorecard

Our Performance Metric Asks Are Counties using NOAA’s positioning products and services?  NOAA looks at County Online Positioning User Service (OPUS) use as a proxy. Have there been 25 or more OPUS solution generations in a given county in the last 12 months?  Counties meeting the above criteria are “substantially enabled” (shaded yellow). Is there feedback and interaction between the local community and NOAA?  Is the County in a State that participates in the NOAA State Advisor/Coordinator program?  Has a County Geospatial Representative been identified (eg County Surveyor, County Engineer, GIS Administrator, or equivalent)?  Has “blue book” data from the County been submitted to NGS through activities such as: leveling project software, GPS projects and OPUS DB (when available)?  Has a County Scorecard web survey been filled out by the County Geospatial Representative?  Counties meeting the above criteria are “fully enabled” (shaded green). County Scorecard Details

NOAA’S County Scorecard How you can help …

NSRS Coordinate Systems Latitude & Longitude State Plane Coordinates UTM Coordinates U.S. National Grid Earth-Centered Earth-Fixed NAD 83 NAD 27 NAVD 88 NGVD 29 ITRF00 ITRF05

Coordinate Confusion DATUM TAGS … are the following all the same? NAD_83(CORS96) NAD 83 (CORS) NAD_83 Position (EPOCH ) NAD_83(CORS96) (EPOCH: ) NAD83 (NSRS2007) NAD 83 (2007) WGS_84(original) WORLD GEODETIC SYSTEM 1984 … how many WGS84’s have there been?

What’s A Person To Do? USER BEWARE – software is suspect re: datums and conversions HTDP – use it to test coordinates FUTURE … - NGS will provide simple transformation tools between datums and reference frames used by NGS - HTDP will evolve to include vertical transformations … TDP

HTDP NAD_83(CORS96) to WGS-84(original)

The NGS 10 year plan

G ravity for the R e-definition of the A merican V ertical D atumG ravity for the R e-definition of the A merican V ertical D atum Official NGS policy as of Nov 14, 2007 –$38.5M over 10 years Airborne Gravity Snapshot Absolute Gravity Tracking Re-define the Vertical Datum of the USA by 2017 Q: What is GRAV-D? A: A Plan (released Dec 2007)

The first, middle and last point of GRAV-D: Gravity and Heights are inseparably connected Or (to borrow from a common bumper sticker): –No gravity, no height –Know gravity, know height Q: What is GRAV-D? A: Gravity to determine heights accurately

Fast, Accurate Orthometric Heights GPS already gives fast accurate ellipsoid heights If the geoid were determined to highest accuracy… Voila… Fast, accurate orthometric heights –Anywhere in the nation –Time-changes to H determined through: GPS on CORS (h changes) Absolute gravity spot checks (N changes)

GRAV-D Airborne gravity –Critically needed as a one-time high resolution “snapshot” of gravity in the USA As opposed to the thousands of surveys, with hundreds of instruments and operators over dozens of years –One time survey Absolute gravity –Cyclical for episodic checks in fixed locales –Co-incident with foundation CORS? –Two field meters plus one fixed SG Relative Gravity –More frequently attached to “Height Mod” surveys

National Readjustment

New Standards for Geodetic Control Local accuracy Relative to Adjacent Points Network Accuracy Relative to CORS Both are relative accuracy measures at 95% confidence Will not use distance dependent (proportional) expression of accuracy Order/Class codes (A, B, 1, etc.)

Example Datasheet with new Accuracies

FGDC Standards for Geodetic Control

Future Changes? The published CORS coordinates based on ITRF2000 define the new NAD 83 (NSRS2007) coordinate system When the next version of ITRF is available NGS will probably adopt it and revise the CORS coordinates … within a couple of years

OPUS-RS Accuracy for 15-minute data sets