Progress Towards the Seamless Combination of Bathymetric and Topographic Data in New Zealand

Transcription

1 Progress Towards the Seamless Combination of Bathymetric and Topographic Data in New Zealand Matt Amos Senior Technical Advisor National Geodetic Office

2 Introduction Datasets usually defined in terms of different vertical datums and reference surfaces Topography MSL Hydro LAT/CD Cadastral MHWS Geodesy MSL & ellipsoid Challenge is to combine different datasets

3 2006 Height Integration Study Main recommendations: Ellipsoidal heights to be used as transformation medium Define transformations between local datums and sea levels GRS80 be adopted as a common reference system Develop national DEM Map coastal zone with marine/terrestrial LiDAR

4 NZ Vertical Datum 2009 Based on NZGeoid2009 Normal-orthometric heights Aligned to GRS80 Offsets to local datums ±8 cm nationally ±2 15 cm locally 2-3 cm would meet most user needs Supports dataset integration through defined datum offsets

5 Vertical Datum Improvement Project to reduce the following weaknesses of NZVD2009: Inaccuracies in the geoid model Inaccurate relationships to other datums Small number of defined relationships Resolving these weaknesses is key to supporting data integration

6 Airborne Gravity Survey Airborne gravity gives regular coverage irrespective of terrain Efficient method of improving gravity database Collect over a short timeframe Should enable 2-3 cm accuracy when combined with existing data in flat areas Test survey planned in Canterbury in April 2012

7 Airborne Gravity Survey Area

8 Offset Improvement Constant offset approach is simplistic Assumes distortion-free flat datum Determined from limited GPS-levelling observations Probably not representative across entire datum Offsets only published to 13 major datums NZVD2009 uptake limited by small number of offsets May need unique offsets/relationships for each datum or dataset

9 Offset Improvement Evaluate other methods of relating datums Inclined planes Polynomial surfaces Increase number/coverage of GPS-levelling points Improves offset calculation for major datums Provides more field check points Provide links to more vertical datums Develop process to include new datums Seek user suggestions for datums to be added

10 Imagery Coordination Public sector initiative to: Improve efficiency of acquisition Promote free re-use of data Includes land and sea coverage Will enable easy access to imagery products Increase demand for integrated datasets

11 National Elevation Framework Initiative to develop a national DEM Framework to allow other models to align Likely to extend offshore so bathymetric datasets could be included to create seamless models Requires data to be collected or stored in a consistent/compatible vertical datum

12 Marine and Terrestrial LiDAR Enables seamless data collection across land/sea interface Terrestrial LiDAR used extensively for elevation modeling Supports national DEM initiative Planned trial marine acquisition in December 2011 was deferred by inclement weather

13 LINZ Data Service

14 LINZ Data Service Provides free online access to a large number of LINZ datasets Released under creative commons license Includes 5 hydrographic & maritime datasets, including data from LINZ ENC products Enables integration of datasets Reliant on defined transformations

15 LINZ Data Service Demonstration at 12:50 today at the LINZ exhibition stand Downloading vector data to different applications Accessing vector data via LINZ web services

16 Summary LINZ has been working on the integration of topographic and bathymetric data for some time NZVD2009 has provided a useful transformation surface to enable combination Current initiatives include: Upgrade to NZVD2009 Imagery coordination National elevation framework Marine & terrestrial LiDAR LINZ Data Service

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