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Datums and Shifts

Datums and Shifts. Most coordinate systems are referenced to a specific datum Mix two different datums for the same point. Shift. NAD83?, WGS84? And ITRF?. NAD83 (1986) = WGS84 (G730) first GPS version NAD83 (CORS96) ≠ WGS84 (G1150) WGS84 (G1150) = ITRF00 Autonomous GPS = ITRF00

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Datums and Shifts

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  1. Datums and Shifts Most coordinate systems are referenced to a specific datum Mix two different datums for the same point Shift

  2. NAD83?, WGS84? And ITRF? • NAD83 (1986) = WGS84 (G730) first GPS version • NAD83 (CORS96) ≠ WGS84 (G1150) • WGS84 (G1150) = ITRF00 • Autonomous GPS = ITRF00 • SBAS = ITRF00 • CONUS DGPS Beacon = NAD83(CORS96) • Reference Stations = NAD83 (some epoch date)

  3. Datum Adjustments WGS84 (G1150) – most current version “Original” NAD83 = NAD83 (1986) NAD83 (1992) NAD83 (CORS96) (Epoch 1997.00) NAD83 (2002) NAD83 (NSRS2007) NAD83 (2011) Know your NADS

  4. Over Time Datums Have Grown Apart WGS84 = ITRF00(2cm) NAD83 NAD83 (1986) = WGS84 ~ 1 meter Difference between WGS84 and NAD83

  5. Step 1. Verify Datum in GIS Standardize on NAD83! Convert NAD27 to NAD83 using NADCON Special Cases Require Care Consider Scale of Data

  6. Step 2. Confirm the GPS Reference Frame Which Reference Frame are you In? WGS84 /ITRF00 I’m in NAD83

  7. Step 3. Apply the Correct Transformation Use Zero Transformations when Appropriate If NDGPS differential If VRS or Single Base is in NAD83 If using CORS – Reference Position from Base File NAD83 Reference Frame If post-process CORS, WAAS – ITRF00 Reference Frame If using Trimble Base Provider List or Reference Position from Base Provider If using WAAS If using Autonomous Transform using NAD83 (CORS96) Do Nothing! See Handout for Trimble and ArcPad Users

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