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Overview of the Canadian Spatial Reference System and WGS84 vs NAD83 Reference Systems

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This presentation provides an in-depth look at the Canadian Spatial Reference System (CSRS) and the key aspects of the WGS84 and NAD83 reference systems. It covers their alignment, transformations, and historical updates, focusing on coordinate accuracy, datum shift parameters, and various ITRF alignments. The information addresses applications in GPS technology and GIS software, explaining how these systems relate to real-time positioning data and their practical implications for geographic and spatial sciences.

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Overview of the Canadian Spatial Reference System and WGS84 vs NAD83 Reference Systems

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  1. Earth Sciences Sector Earth Sciences Sector Earth Sciences Sector Canadian Spatial Reference System Additional slides For CGRSC Sept 18-20, 2006

  2. Dynamic Fixed 1987WGS84 - same reference system as NAD83 (+/- 1m) 1986NAD83 (Orig)- NAD83 reference system based on Doppler- Coordinate shifts of 1.5 m horizontally, 1 m vertically- metre-accuracy NAD83 Fixed 1988ITRF88 - geocentric ITRF89ITRF90ITRF91ITRF92ITRF93ITRF94ITRF96ITRF97ITRF2000 Dynamic 1994WGS84(G730)- aligned with ITRF91- 1.5 m different from NAD83 Small incremental changes 1997WGS84(G873)- aligned with ITRF94 2001WGS84(G1150)- aligned with ITRF2000 Reference Systems - Timeline NAD83 WGS84 ITRF 1998NAD83 (CSRS)- same NAD83 reference system- same geocentre error- same axis misalignment- cm-accuracy NAD83

  3. NAD83(CSRS) vs NAD83(Orig.) Stations re-observed with high-order GPS Provincial Grid Shift Files

  4. WGS84 - NAD83(CSRS) shift in 1997 Datum Transformation Parameters

  5. Datum Shift in GPS receivers/software • Usually 3-parameter datum shift • Datum Shift Table published by NGA (National Geospatial-Intelligence Agency)formerly NIMA http://earth-info.nga.mil/GandG/publications/tr8350.2/tr8350_2.html From June 23, 2004 update • The WGS84-NAD83 datum shift values date back to 1987 when WGS84 and NAD83 were the same • If you set your receiver to • WGS84 no datum shift is applied (GPS native datum) • NAD83 a zero datum shift is applied (which is incorrect) • Either way you’re in WGS84

  6. Datum shift in GIS software • 7-parameter datum shift values are often used (e.g. ArcPad) • Datum Shift Table published by NATO • Most GIS software • expect realtime position data (NMEA stream) to be in WGS84 • can apply a WGS4-to-Local datum shift http://earth-info.nga.mil/GandG/coordsys/datums/helmert.html • WGS84-to-NAD83 is a Zero-shift here as well

  7. GPS fix code (1=GPS, 2=DGPS, 3=PPS, 4=RTK, 5=Float RTK) Time 15:55:32 # of Sats HDOP Latitude Longitude (in degrees and decimal minutes) H =h-N h=H +N Ellipsoidal Height originally computed by receiver = 73.7m – 34.1m =39.6 m NMEA realtime position format H N Geoid Height MSL Height No data field for Datum WGS84 Geoid height is applied

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