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Vertical Datum Issues in New Zealand

Vertical Datum Issues in New Zealand. Nic Donnelly – Geodetic Data Analyst 5 March 2008. Global Context. New Zealand Height Systems. Unlike the US, New Zealand does not have a single national vertical datum 13 major leveling datums (and many minor local datums)

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Vertical Datum Issues in New Zealand

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  1. Vertical Datum Issues in New Zealand Nic Donnelly – Geodetic Data Analyst 5 March 2008

  2. Global Context

  3. New Zealand Height Systems • Unlike the US, New Zealand does not have a single national vertical datum • 13 major leveling datums (and many minor local datums) • Datum origins in terms of MSL at 12 different gauges Major Leveling Datums

  4. Issues • Most vertical datums in NZ were defined over short time frames (1-2 years) in non-ideal locations so they may not represent long term MSL • MSL changes over time (~50 years since datums defined) • Orthometric heights only on benchmarks beside major highways – sparse coverage • Nationwide leveling inefficient

  5. Height Modernization FROM THIS TO THIS

  6. NZGeoid05 • NZGeoid05 developed in conjunction with Curtin University of Technology, Perth, Australia • Geoid determined using the following datasets: • Terrestrial gravity observations • Marine gravity observations • Satellite altimetry • Digital topography data • Global geoids • Geoid verified with: • GPS derived heights • Leveling derived heights Marks with GPS and Precise Leveling Heights

  7. NZGeoid05 • A gravimetric geoid (as opposed to geometric) • Ranges from 0 to 40 m above GRS80 ellipsoid • Provided on a 2 arc-minute grid (~3.7 km) • Sub 10 cm nationwide accuracy at this resolution

  8. NZGeoid05 Accuracy

  9. NZ Vertical Datum • Ellipsoidal heights authoritative • Geoid plus offset used to transform from ellipsoid to leveling datums • Offsets can also be used to transform heights between leveling datums (even if they don’t overlap)

  10. Height Modernization Products • Ellipsoidal heights on about 20000 geodetic marks • Online height conversions to obtain orthometric heights • Downloadable conversion software • Geoid grid files available • Continued maintenance of existing benchmark infrastructure

  11. Next Steps • Surveyor-General Vertical Datum standard • Continued education of the spatial community to encourage geoid model usage for appropriate purposes • Maintenance plan for geoid and existing benchmark network • Possible update when EGM08 becomes available

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