Spatial Data Infrastructure (PowerPoint) by chenmeixiu

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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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