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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
11
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
12
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}
16
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
18
Geocentric Datum of Australia
Distortions between Distortions between Transformed AGD84 and GDA94Transformed AGD84 and GDA94
Western Qld Central Coast
19
Geocentric Datum of Australia
Coordinates Systems Coordinates Systems and Projectionsand Projections
X
Y
Z
h
- X+ Y- Z
N
E
20
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
22
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
23
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