2/4/2020 COORDINATE SYSTEMS, DATUMS AND MORE Wisconsin Society of Land Surveyors Conference Wisconsin Dells, 2020 1 PRESENTATION OUTLINE A mostly non-technical look at survey coordinates Coordinate system components TYPE OF COORDINATES New U.S. datum strategies ELLIPSOIDS 2022 COORDINATES WGS84 U.S. SURVEY FOOT PROJECTIONS HTDP FALSE NORTHINGS & EASTINGS / ORIGINS DATUMS EPSG DATASET Other coordinate system considerations GEOIDS – GRACE PATCHWORK IS BECOMING GLOBAL EPOCHS ITRF TABLECLOTHS GEOCODING REGIONAL COORDINATES USER SOFTWARE – FIELD AND OFFICE HOUGHTEAM Realizing coordinates in the field NORTH CORS AND NETWORKS NETWORK DATUMS OPUS REPORTS PPP COORDINATE CALIBRATIONS SC104 COORDINATE TRANSFORMATION ANTENNAS 2 COORDINATE SYSTEM MECHANICS Coordinate System Components 3 1 2/4/2020 TYPES OF COORDINATES • Number line • Plane • Polar • Cylindrical • Cartesian GNSS use a hypotheoretical location as the centroid of an ellipsoidal model that best fits the earth’s shape. 4 ELLIPSOIDS WGS84 (G1762) is the current ellipsoid being used by GPS • NAD83 coordinates are based on the GRS80 ellipsoid model • NAD27 coordinates are based on the Clark ellipsoid of 1866 • Trimble Business Center has at least 219 ellipsoid models in its database • Additional custom models can be created 5 WGS84 Semi-major axis 6378137 m | Semi-minor axis 6356752.31424518 m Flattening (1/f) 298.25722356301 | Eccentricity 0.0818191908426202 Year Realization (Epoch) Practical equivalent to… 1987 WGS1984 (Original) NAD83 (1986) 1994 WGS1984 (G730) ITRF91/92 1997 WGS1984(G873) ITRF94/96 2002 WGS1984 (G1150) ITRF00 2012 WGS1984 (G1674) ITRF08 2013 WGS1984 (G1762) Compares to ITRF08 within 1 cm RMS Source: https://rplstoday.com/community/gnss-geodesy/datums-2/paged/2/ 6 2 2/4/2020 PROJECTIONS Four types of projection distortions can occur • Distortions include: Shape, Size, Direction, Distance • Transverse Mercator generally used in North/South regions • Lambert Conformal generally used in East/West regions • Oblique Stereographic generally used in 1-step transformations The Universal Transverse Mercator system 7 MAP DISTORTION EXAMPLE Abu Dhabi to Los Angeles 8 FALSE NORTHINGS & EASTINGS / ORIGINS A look at Sauk County WISCRS projection • Transverse Mercator • Origin is near Blanchardville, WI • False Northing 0.017 Survey Foot • False Easting 609000.001 Survey Feet • Approximate Ground to Grid ratios • Low distortion • 1:500,000: Baraboo, Reedsburg, Wisconsin Dells, Lake Delton 9 3 2/4/2020 DATUMS The NGS defines the official geodetic datums for all federal mapping activities in the U.S. and its territories as part of the National Spatial Reference System (NSRS) • NAD27 NAD83 (NSRS2007) National Readjustment • NAD83 • NAVD88 • NAPGD2022 • Will be based on the IGSxx Time- Dependent Reference Frame https://www.ngs.noaa.gov/NationalReadjustment/ 10 EPSG DATASET International Association of Oil & Gas Producers European Petroleum Survey Group • Search the database http://www.epsg.org for "Sauk" 11 EPSG DATASET International Association of Oil & Gas Producers European Petroleum Survey Group • Search the database for "Sauk" • View the parameters for EPSG 7631 • Many organizations have suggested using the EPSG code for broadcasts from GNSS base stations to rovers. In this way, rovers have the possibility to be calibrated automatically into the active coordinate system regardless of brand and with homogeneity of the datum. 12 4 2/4/2020 GEOIDS – GRACE Heights to Elevations Earth Mass Center WGS84 GEOID Ellipsoid Ellipsoid Geoid Topographic Surface 13 GEOIDS – GRACE Gravity Recovery And Climate Experiment 14 EPOCHS Coordinates change over time • Reference Frames have Realizations • NAD 83(CORS96) active control • NAD 83(NSRS2007) passive control • Realizations have Epoch dates • NAD 83(2011) epoch 2010.00 15 5 2/4/2020 ITRF International Terrestrial Reference Frame EPSG NAME EPOCH • Realization of the ITRS, International CODE Terrestrial Reference System* ITRF92 1988.0 4914 ITRF93 1988.0 4915 • ITRF and ITRS realizations are managed by ITRF94 1993.0 4916 the IERS, International Earth Rotation and ITRF96 1997.0 4917 Reference Systems Service* ITRF97 1997.0 4918 • Current global standard ITRF2000 1997.0 4919 ITRF2005 2000.0 4896 • New datums from the NGS will align with the ITRF2008 2005.0 5332 current ITRF** ITRF2014 2010.0 7789 *https://en.wikipedia.org/wiki/International_Terrestrial_Reference_System_and_Frame **https://www.ngs.noaa.gov/datums/index.shtml 16 REGIONAL COORDINATES Many regions have localized coordinates • States including Wisconsin, Minnesota, Indiana and Iowa have created County based systems • Networks are using the RTCM Coordinate Transformation Messages to inform rovers about datum parameters • One-Step transformation to locally based Ground Control Points is still very common 17 GNSS APPLICATIONS AND INFRASTRUCTURE Realizing Coordinates in the Field 18 6 2/4/2020 CORS AND NETWORKS Thousands of Continuously Operating Reference Stations around the world form networks of GNSS receivers 19 NETWORK DATUMS Real-time network corrections define the datum at the rover • NAD83-2011 Epoch 2010.0 • Some networks are commercial enterprises • WRTN, ODOT, ORGN, TURN, INCORS, • Some networks are public NYSNet, WISCRS, IaRTN, TxDOT infrastructure with varying fee based • CRTN – NAD83-CSRS Epoch 2017.50 access • Some network datums are • TGRN – NAD83 (1995) constrained by historical, financial or • GDA2020 – ITRF2014 Epoch 2020.0 other considerations 20 OPUS REPORTS OPUS Worldwide Post-Processing Service • Static RINEX files (*.YYo) can be uploaded to https://www.ngs.noaa.gov/OPUS/ to be processed into the NSRS (National Spatial Reference System) • If the submission includes a zero antenna height, OPUS will provide a warning/notice • Other file requirements include: Dual- frequency GPS between 15 minutes and 48 hours in duration 21 7 2/4/2020 OPUS REPORTS (2) OPUS Worldwide Post-Processing Service • Information about the satellite orbits is in the Ephemeris file • There are three releases for a day's orbit file • Each release is slightly more accurate https://www.ngs.noaa.gov/orbits/orbit_data.shtml 22 OPUS REPORTS (3) OPUS Worldwide Post-Processing Service • RINEX NAV files contain constellation specific details: Satellite health, transmission time of message and fit interval • The correct antenna model and antenna height above the marker can be selected • The NGS manages a database of absolute geodetic antenna models to minimize azimuth and elevation dependent errors 23 OPUS REPORTS (4) OPUS Worldwide Post-Processing Service • Overall (3D) RMS for this collection is calculated to be 0.017 meters • Solution is presented in two different reference frames as… • ECEF coordinates • Latitude and Longitude • Ellipsoidal Height • Geoidal Height and model that was used 24 8 2/4/2020 OPUS REPORTS (5) OPUS Worldwide Post-Processing Service • Coordinates are also provided in global UTM and State Plane projected systems • Convergence angle (+/-) to the projected system's central meridian • Horizontal point scale – grid to ground • 3D Combined point scale – grid to ground • CORS data that was used to process the position is provided 25 PPP Precise Point Positioning (State Space Representation) • The goal is to achieve under 4 centimeters of accuracy PPP-RTK anywhere in the world with PPP - State space PPP-Network - State space - Local/Regional - Observation no internet access - Global - Ambiguity State space - No ambiguity resolution - Local/Regional resolution - Cm accuracy - Ambiguity - Dm accuracy resolution - Cm accuracy https://iotbusinessnews.com/2011/12/20/68809-u-blox-achieves- sub-meter-gps-accuracy-with-ppp-precise-point-positioning/ 26 COORDINATE CALIBRATIONS . Site Calibrations Turning global coordinates into Name Horz Vert North Error East Error Vert Error 1 Yes Yes 0.0000.0080.0050.0070.006 0.0000.0080.0060.0120.011 0.0000.0090.0080.007 survey points “The2 Yesproof Yes is 0.0000.0050.0080.009 in the 0.0000.0070.0090.010 dirt!” 0.0000.0100.0140.006 3 Yes Yes No 0.0060.0040.0050.008 0.0100.0090.0080.007 0.0000.0400.048-.--- 4 Yes Yes 0.0010.0030.005 0.0050.004 0.0030.004 5Phil Yes No Stevenson, Yes 0.033-.--- 0.076 -.---PLS0.009 0.011 Global LLH 2 points define rotation and scale 5 points provide Datum redundancy checks 3 points create a plane and Local LLH Project generate Hz residuals Area Map Projection Geoid 4 points generates Hz and Vt residuals Grid Y,X Z 1 point – North rotation, Scale = 1 27 9 2/4/2020 SC104 COORDINATE TRANSFORMATION RTCM Special Committee 104 has developed messages that can automate the coordinate calibration process from the server side Message Type Message Name 1021 Helmert/ Abridged MolodenskiTransformation Parameters 1022 Molodenski-BadekasTransformation Parameters 1023 Residuals, Ellipsoidal Grid Representation 1024 Residuals, Plane Grid Representation Projection Parameters, Projection Types other than Lambert 1025 Conic Conformal (2 SP) and Oblique Mercator Projection Parameters, Projection Type LCC2SP (Lambert 1026 Conic Conformal (2 SP)) 1027 Projection Parameters, Projection Type OM (Oblique Mercator) 1028 (Reserved for Global to Plate-Fixed Transformation) 28 ANTENNA GNSS antennas vary Magellan 111406 L1 Offset – 6.01 cm (2.37”) • PCV = Phase Center Variation • ARP = Antenna Reference Point Spectra Epoch 35 L1 Offset – 9.97 cm (3.93”) 90° 90° Phase Center Phase Center 0° 0° Spectra SP60 Antenna Reference Point Antenna Reference Point L1 Offset – 5.05 cm (1.99”) Phase Meter Phase Meter +π +π 0.f λ 0.f λ -π -π Elevation Elevation