Spatial Data Infrastructure

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Spatial Data Infrastructure

• Geodetic Infrastructure

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Objective

• To understand the role of Geodesy in SDI and Land
  Administration

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Overview

• Geodesy and Geodetic Datums in Australia
• Geodetic requirements of SDI
• Case Study PCGIAP
• Case Study Vicmap Digital Property
• Victorias Geodetic Strategy

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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)

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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

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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

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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

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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

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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

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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)

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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

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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

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PCGIAP ...
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Source (Rajabifard and Williamson, 2001)
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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

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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

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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)

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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

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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

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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

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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

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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)

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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

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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

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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

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Questions?