Geocentric Datum of Australia Geocentric Datum of Australia (GDA) Peter Todd Project Manager GDA Implementation ICSM Matt Higgins Technical Manager GDA Implementation

Geocentric Datum of Australia Standard Time Act(1894) Standard Time Act (1894) “... a traveller from Brisbane arriving in Toowoomba will find his watch four minutes fast. Exactly so. And it will be fast. Let him set it right. Are all the people in Toowoomba to keep their watches wrong to oblige a few strangers? Why should it be that the convenience of the man who is travelling should be preferred to the ninety-nine who stay at home?” ( The Professional Officer, p13 )

Geocentric Datum of Australia Who will GDA Impact? l Spatial Information Management (including collection, manipulation and presentation) l Uses Spatial Information Products l Integrate Spatial Information l Manage Information that has a Spatial Extent.

Geocentric Datum of Australia Magnitude of Shift l All coordinates will shift in excess of 200m. l Australia will adopt GDA on 1 January 2000.

Geocentric Datum of Australia Terminology GDA94AGD84 Latitudes & Longitudes AMG84MGA94 Eastings, Northings & Zone Universal Transverse Mercator Std. 6 Degree Zones, with the same Central Meridians etc.

Geocentric Datum of Australia Datum & Spatial Data l Evolution of Geodetic Datum l Negative Impact resulting from the precision of AGD l Multiple Datum l International Agenda l International Environmental Data l Australian Spatial Data Infrastructure l Qld Information Council (QSIIC) l Qld Industry Group (QSIIG)

Geocentric Datum of Australia Mapping Standards l Australian Defence Forces adopted a geocentric Datum in June 1992 l Aeronautical & Hydrographic organisations will adopt GDA by 1998 l Dept. Natural Resources will adopt GDA by mid 1998

Geocentric Datum of Australia Technology Issues l Commercialisation of GPS l Changing nature of the typical GPS user l Diverse applications l Future positioning systems l Impact of GIS l Breadth of GIS applications l AM / FM l Fundamentals of Corporate Information Management l Spatial Engines

Geocentric Datum of Australia AGD l Terrestrial Observations l Systematic Errors l Constrained by Doppler (transformed) l Distribution l Homogeneity l Location of Marks

Geocentric Datum of Australia GDA l GPS Observations l Small Random Errors l Constrained by GPS l Distribution l Homogeneity l Marks are Accessible

Geocentric Datum of Australia 11 The Geoid (Mean Sea Level) Local Datum AGD84 (best fits Australia) Geocentric Datum (best fit globally) Ellipsoids and Geoids

Geocentric Datum of Australia 12 Reference Frames l International Terrestrial Reference Frame (ITRF) is a particular “realization” of an idealized reference system... l observation at certain sites and with certain factors in the processing produces... l set of positions and velocities of those sites at a certain time. l reference ellipsoid - GRS80

Geocentric Datum of Australia Progress to Date l Recognise the need to adopt a geocentric datum. l Resolution 2: … recommend the adoption of an appropriate geocentric datum on 1 January l ICSM Supports a National GPS Campaign.

Geocentric Datum of Australia Progress to Date l 100 km Network commenced in QLD l Adjustment of 100 km and GMA82 data sets constrained to the AFN & ANN. l Adjustment of secondary networks. l Densification of control. l Network management & datum extension.

Geocentric Datum of Australia AGD to GDA Block Shifts Coordinates Shift { 10 metres } 7 Parameter Transformation Coordinate Shifts; Rotations and Scale { 2-3 metres } Readjustment Readjust observations constrained to GDA coordinates Coordinate Shifts; Rotations and Scale plus Distortion Model Distortion Model { abt. 5 cm }

Geocentric Datum of Australia 16 Datum Transformation l 3D Transformation between GDA94 and AGD84 l 7 Parameters : 3 Shifts, 3 Rotations and 1 Scale l Presently use “Higgins 1987” Parameters l New Parameters - Late 1997 l To be supplemented with a grid of corrections to model remaining distortion due to errors in AGD84 Y X Z Y X Z Dx Dy Dz Rx Ry Rz

Geocentric Datum of Australia The Source of these Distortions Shift determined from 7 Parameter Transformation (most of 200m shift) True GDA True AGD abt. 110 m abt.190 metres Shift determined from Distortion Modelling (Most of what’s left) 2-3 metres abt. 5cm

Geocentric Datum of Australia 18 Distortions between Transformed AGD84 and GDA94 Western QldCentral Coast

Geocentric Datum of Australia 19 Coordinates Systems and Projections X Y Z  h - X + Y - Z N E

Geocentric Datum of Australia 20 Coordinates Systems and Projections N AMG N MGA E MGA E AMG

Geocentric Datum of Australia Universal Transverse Mercator Projections 147 o 150 o 144 o Scale Factor o wide zones ZONE 55ZONE 54ZONE 56

Geocentric Datum of Australia 22 Effect of Ellipsoid Size and Shape on Map Sheets GDA AGD same lats and longs difference in eastings and northings equator

Geocentric Datum of Australia 23 The Three Dimensional Nature of GDA H (AHD) Topography Geoid (MSL) N (GDA) h (GDA) Ellipsoid (GDA) h (AGD) N (AGD) Ellipsoid (AGD)

Geocentric Datum of Australia Implementation Plan l January 1998  Cabinet Endorsement; Methodologies; Communication, Education. l July 1998  Data sets; Standards; Pilots; Tools; Communication. l July 1999  Implementation; Support; Communication.

Geocentric Datum of Australia Strategy l Technical & Quality Standards l Decision by your Partners (clients and data suppliers) l Accuracy & reliability Standards l Mapping Practices l Technical Competencies l Product Options l Presentation Issues l Software Compatibility l Contractural Issues l Time Frames

Geocentric Datum of Australia What is the Latest? l GDA List Server l Implementation Team  Hotline & GDA Group l Web Sites  ICSM & AUSLIG (National Implementation)  QSIIC & QSIIG (Spatial Infrastructure)  GIS & GPS vendors  Your Web Site

Geocentric Datum of Australia Geocentric Datum of Australia (GDA) Peter Todd Project Manager GDA Implementation ICSM Matt Higgins Technical Manager GDA Implementation