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Spatial Data Infrastructure Geodetic Infrastructure Objective • To understand the role of Geodesy in SDI and Land Administration Overview • Geodesy and Geodetic Datums in Australia • Geodetic requirements of SDI • Case Study: PCGIAP • Case Study: Vicmap Digital Property • Victoria‟s Geodetic Strategy Geodetic Datum • A mathematical approximation of the geoid for specific area • Comprised of: – Reference frame (defines axes, eg CIO) – Ellipsoid (mathematical representation of the Earth, eg ANS, GRS80, WGS84) – Origin (location and orientation defined by ground marks, eg AFN, Johnston Geodetic Station) Coordinate Systems • Different methods of representing the same coordinates • E.g. geographic/geodetic, Grid (UTM), Cartesian (XYZ) • Geodetic latitude, longitude and height recently adopted by Victoria as the preferred system for storing geographic data Old Geodetic Datum • AGD 66 – based on Australian National Spheroid (ANS) – origin displaced from the centre of the earth by about 200m – No geoid model used – inhomogeneous scale and orientation – replaced in some states (WA, Qld) by AGD84 – UTM coordinates known as AMG New Geodetic Datum • GDA 94 – based on GRS80 ellipsoid (civilian version of WGS84) – global best fit to geoid – geocentric – homogeneous – national datum – will be used for several decades Geodetic Requirements of SDI • Purpose of SDI to enable effective collection, management, access, delivery and utilisation of spatial data in a local, national, regional or global community • Geodesy forms the foundation of the individual data sets and is needed to relate one data set to another Geodetic Requirements of SDI ... • Transformation of Coordinates – data from many sources using a variety of geodetic datums – often transformation between datum does not model errors correctly – preferable to re-adjust – good practice to relate national datum to ITRF – E.g PCGIAP Pilot Project Geodetic Requirements of SDI ... • Connection / use of control – data collected without direct use of the geodetic infrastructure – problems with heterogeneity – E.g. Victorian Cadastral Map (Vicmap Digital Property) Case Study - PCGIAP • Committee to support the use of GIS for social, economic and environmental objectives of the 55 member countries • Regional Geodetic Network Working Group • Establishment of a regional datum and transformation parameters is a fundamental component PCGIAP ... • Lack of geodetic infrastructure in many countries – no zero order control, horizontal datum, vertical datum, geoid models, unknown tectonic movements etc. • Due to cultural differences and/or military control over mapping activities many nations do not wish to share data PCGIAP ... Australia Hong Kong Indonesia Sri Lanka Thailand Horizontal Datum GDA94 Hong Kong Unknown / Everest 1980 Indian Datum (ITFR92 @ 1980 Geodetic Not 1975 1994.0) Datum and Specified WGS84 Ellipsoid GRS 80 Hayford 1910 Unknown / Everest Unknown / and WGS84 Not Not Specified Specified Vertical Datum AHD Hong Kong Unknown / MSL with Unknown / Principle Not one tide Not Specified Datum Specified gauge Geoid AUSGeoid98 Not Defined Unknown / Unknown / Unknown / Not Not Not Specified Specified Specified Permanent GPS, SLR, GPS Unknown / GPS Unknown / Geodetic Facilities VLBI, DORIS Not Not Specified Specified Techtonic No Unknown Unknown / No No Movement Not Problems Specified Source: (Rajabifard and Williamson, 2001) PCGIAP ... • Asia Pacific Regional Geodetic Project • GPS/SLR/VLBI campaigns to establish: – station coordinates and velocities in an ITRF system – problems caused by tectonic movements – a regional horizontal and vertical datum – transformation parameters between local systems and the regional datum Case Study - Vicmap Digital Property • Digital cadastral map of Victoria • Contains most private and Crown properties in Victoria • Used by over 300 organisations • Data collected by: – digitisation of maps – direct entry of bearings and distances – digital plans of new subdivisions Vicmap Digital Property ... • Stated accuracy of 0.1m to 25m is a function of: – scale of map used for digitisation, and – method of isolated surveys used in Victoria • Updating (within 10 days of receipt of plan) • Upgrading - the “shifting cadastre” – requirement to connect to AMG in Victoria since 1995 (earlier in proclaimed survey areas) Vicmap Digital Property ... • Utility of cadastre Lower Utility Digital DCDB Upgraded DCDB Survey Accurate Cadastral Model Reinstate-able Cadastral Model Legal Coordinates Cadastre Higher Utility Vicmap Digital Property ... • Review of Cadastral Requirements of Geodetic Surveying Infrastructure, Nov 2000 – An „unhealthy‟ percentage of surveyors choose not to comply with current legislation regarding connection to control – Certification of the accuracy of the connection is required by the surveyor – Surveyors do not seem to understand the benefits of connecting to control Vicmap Digital Property ... • New Zealand – Surveyors submit observations instead of property boundaries – Must connect to control (unless permission not to do so is granted) and meet certain integrity and redundancy requirements – Adjustment is done by LINZ – Cadastral marks are regarded as geodetic marks Vicmap Digital Property ... • Queensland – Parts of the cadastral map with suspect accuracy are „carpet bombed‟ using RTK GPS to get good coordinates for property boundaries Victorian Geodetic Strategy • Reduce need for ground marks • Maintain the same minimum accuracy across the state • Support economic and efficient positioning state-wide for a wide range of users • Encourage adoption of GDA94 • GPS base station network (GPSnet) GPSnet • Around 20 continuously operating GPS reference stations across the state • Nominal spacing of 100km across Victoria, 50km in the metropolitan area • Geodetic, dual frequency receivers • Users can down load data at a small cost • Will become part of the national adjustment GPSnet ... • Hesitation by surveyors to use GPS for cadastral surveying – Cost of GPS, especially for the predominantly small cadastral surveying companies in Victoria – Practicality in urban and wooded areas – Lack of confidence/understanding of achievable accuracy – Legal traceability Research • Automatic integrity monitoring of GPSnet – Quality control of raw data – Detection of reference station movement • Stochastic modelling to asses uncertainty in GPS and provide better measures of precision Questions?
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