Geocentric Datum of Australia

Geocentric Datumof Australia(GDA)

Peter Todd

Project Manager

GDA Implementation ICSMICSMMatt Higgins

Technical Manager

GDA Implementation

Geocentric Datum of Australia

Standard Time ActStandard Time Act (1894)(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?Who will GDA Impact?

Spatial Information Management (including

collection, manipulation and presentation)

Uses Spatial Information Products

Integrate Spatial Information

Manage Information that has a Spatial

Extent.

Geocentric Datum of Australia

Magnitude of ShiftMagnitude of Shift

All coordinates will shift in excess of 200m.

Australia will adopt GDA on 1 January 2000.

Geocentric Datum of Australia

TerminologyTerminology

GDA94GDA94AGD84AGD84 Latitudes & Longitudes

AMG84AMG84 MGA94MGA94Eastings, Northings& Zone

Universal Transverse MercatorUniversal Transverse MercatorStd. 6 Degree Zones, with

the same Central Meridians etc.

Geocentric Datum of Australia

Datum & Spatial DataDatum & Spatial Data

Evolution of Geodetic Datum

Negative Impact resulting from the precision of AGD

Multiple Datum International

Agenda

International Environmental Data

Australian Spatial Data Infrastructure

Qld Information Council (QSIIC)

Qld Industry Group (QSIIG)

Geocentric Datum of Australia

Mapping StandardsMapping Standards

Australian Defence Forces adopted a

geocentric Datum in June 1992

Aeronautical & Hydrographic

organisations will adopt GDA by 1998

Dept. Natural Resources will adopt GDA

by mid 1998

Geocentric Datum of Australia

Technology IssuesTechnology Issues

Commercialisation of GPS

Changing nature of the typical GPS user

Diverse applications

Future positioning systems

Impact of GIS Breadth of GIS

applications AM / FM Fundamentals of

Corporate Information Management

Spatial Engines

Geocentric Datum of Australia

AGDAGD

Terrestrial Observations

Systematic Errors Constrained by

Doppler (transformed) Distribution Homogeneity Location of Marks

Geocentric Datum of Australia

GDAGDA

GPS Observations Small Random

Errors Constrained by

GPS Distribution Homogeneity Marks are

Accessible

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Geocentric Datum of Australia

The GeoidThe Geoid(Mean Sea Level)(Mean Sea Level)

Local DatumLocal DatumAGD84 AGD84

(best fits Australia)(best fits Australia)

Geocentric DatumGeocentric Datum(best fit globally)(best fit globally)

Ellipsoids and GeoidsEllipsoids and Geoids

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Geocentric Datum of Australia

Reference FramesReference Frames

International Terrestrial Reference Frame (ITRF) is a particular “realization” of an idealized reference system...

observation at certain sites and with certain factors in the processing produces...

set of positions and velocities of those sites at a certain time.

reference ellipsoid - GRS80

Geocentric Datum of Australia

Progress to DateProgress to Date

Recognise the need to adopt a geocentric datum.

Resolution 2: … recommend the adoption of an appropriate geocentric datum on 1 January 2000.

ICSM Supports a National GPS Campaign.

Geocentric Datum of Australia

Progress to DateProgress to Date

100 km Network commenced in QLD Adjustment of 100 km and GMA82

data sets constrained to the AFN & ANN.

Adjustment of secondary networks. Densification of control. Network management &

datum extension.

Geocentric Datum of Australia

AGD to GDAAGD to GDA

Block ShiftsCoordinates Shift {10 metres}

7 ParameterTransformation

Coordinate Shifts; Rotations and Scale {2-3 metres}

ReadjustmentReadjust observations constrained to GDA coordinates

Coordinate Shifts;Rotations and Scaleplus Distortion Model

DistortionModel

{abt. 5 cm}

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Geocentric Datum of Australia

Datum TransformationDatum Transformation 3D Transformation between

GDA94 and AGD84 7 Parameters : 3 Shifts, 3

Rotations and 1 Scale Presently use “Higgins 1987”

Parameters New Parameters - Late 1997 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 The Source of these Distortionsthese 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

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Geocentric Datum of Australia

Distortions between Distortions between Transformed AGD84 and GDA94Transformed AGD84 and GDA94

Western Qld Central Coast

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Geocentric Datum of Australia

Coordinates Systems Coordinates Systems and Projectionsand Projections

X

Y

Z

h

- X+ Y- Z

N

E

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Geocentric Datum of Australia

Coordinates Systems Coordinates Systems and Projectionsand Projections

NAMG

NMGA

EMGAEAMG

Geocentric Datum of Australia

Universal Transverse Universal Transverse Mercator ProjectionsMercator Projections

147o 150o144o

Scale Factor0.9996

6o wide zones

ZONE 55ZONE 54 ZONE 56

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Geocentric Datum of Australia

Effect of Ellipsoid Size and Effect of Ellipsoid Size and Shape on Map SheetsShape on Map Sheets

GDAAGD

same lats and longs

same lats and longs

difference in eastings difference in eastings and northingsand northings

equatorequator

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Geocentric Datum of Australia

The Three Dimensional The Three Dimensional Nature of GDANature of GDA

H(AHD) Topography

Geoid (MSL)

N(GDA)

h(GDA)

Ellipsoid (GDA)

h(AGD)

N(AGD)

Ellipsoid (AGD)

Geocentric Datum of Australia

Implementation PlanImplementation Plan

January 1998 Cabinet Endorsement; Methodologies;

Communication, Education. July 1998

Data sets; Standards; Pilots; Tools; Communication.

July 1999 Implementation; Support; Communication.

Geocentric Datum of Australia

StrategyStrategy

Technical & Quality Standards

Decision by your Partners (clients and data suppliers)

Accuracy & reliability Standards

Mapping Practices

Technical Competencies

Product Options Presentation Issues Software

Compatibility Contractural Issues Time Frames

Geocentric Datum of Australia

What is the Latest? GDA List Server Implementation Team

Hotline & GDA Email Group Web Sites

ICSM & AUSLIG (National Implementation) QSIIC & QSIIG (Spatial Infrastructure) GIS & GPS vendors Your Web Site

Geocentric Datum of Australia

Geocentric Datumof Australia(GDA)

Peter Todd

Project Manager

GDA Implementation ICSMICSMMatt Higgins

Technical Manager

GDA Implementation