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A changing approach togeodetic networks and standards
MATT AMOS and DON GRANT
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Overview
Historical- Based on method of observation
Current- Based on accuracy achieved
Future
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NZ Geodetic Datum 1949
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Limitations of NZGD1949
“New” technology
- EDM, GPS, etc
Public access to global datasets
Earth Deformation
- Earthquakes
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Edgecumbe 1987 (M6.3)
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Limitations of NZGD1949
“New” technology
- EDM, GPS, etc
Public access to global datasets
Earth Deformation
- 1855 Wellington earthquake – magnitude 8.2
• 18m horizontal
• 2.5m vertical- Continuous deformation
• 5m / century between east and west of NZ
• Motion relative to geo-centre of Earth
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New Zealand Geodetic Datum 2000
GPS-based
Geocentric
Accommodates Earth deformation
Monitored by continuous GNSS
observations
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NZGD2000 Zero Order Network
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NZGD2000 2nd – 4th Order Networks
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NZGD2000 5th Order Network
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Current network still not ideal
Different and conflicting uses Different and conflicting characteristics
- Density
- Accuracy
- Accessibility
- Mark construction
- Site stability Purposes not clear
What exactly do we need?
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Proposed Future Geodetic Networks
Networks defined by purpose (not by process)
Accuracy of networks related to their purpose
not how they are obtained
Different mark characteristics for each
network
Marks can be in multiple networks
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National Reference Frame
Connection to the global frame
One station for each tectonic plate
Continuous GNSS observations
Absolute gravity connection
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Datum Monitoring Network
Maintain accuracy of geodetic datum
Monitor earth deformation
Re-establish cadastre following major
deformation events
Density related to deformation rate
Stability of marks important
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Cadastral Control Network
Geodetic marks to support cadastral surveys
Enable connection to the geodetic datum
Enable orientation to the geodetic datum
Provided where cadastral surveys are being done
Intervisibility important
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Geospatial Network
Alignment of geospatial datasets
Datum connection in areas of little cadastral
activity
- Wilderness areas & National Parks
- Offshore Islands
- Ross Dependency
Marks visible to “aerial” applications
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Next steps
Standard being drafted by LINZ Regulatory Group
Review by expert committee early 2008
Two month public consultation period
Consideration of consultation feedback by committee
Publication of standard late 2008
Networks implemented by LINZ Customer Services
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Summary
Existing geodetic networks based on observation
technique rather than function
New geodetic networks based on purpose
Different networks for different purposes
Draft standard for consultation in early 2008
Standard publication late 2008
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End