Transcript Why Change to GDA

Geocentric Datum of Australia
Geocentric Datum
of Australia
(GDA)
Peter Todd
Project Manager
GDA Implementation
Matt Higgins
Technical Manager
GDA Implementation
ICSM
Geocentric Datum of Australia
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?
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Spatial Information Management
(including collection, manipulation and
presentation)
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Uses Spatial Information Products
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Integrate Spatial Information
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Manage Information that has a Spatial
Extent.
Geocentric Datum of Australia
Magnitude of Shift
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All coordinates
will shift in excess
of 200m.
Australia will
adopt GDA on
1
January 2000.
Geocentric Datum of Australia
Terminology
AGD84
Latitudes &
Longitudes
GDA94
Universal Transverse Mercator
Std. 6 Degree Zones, with
the same Central Meridians etc.
AMG84
Eastings, Northings
& Zone
MGA94
Geocentric Datum of Australia
Datum & Spatial Data
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Evolution of
Geodetic Datum
Negative Impact
resulting from the
precision of AGD
Multiple Datum
International
Agenda
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International
Environmental Data
Australian Spatial
Data Infrastructure
Qld Information
Council (QSIIC)
Qld Industry Group
(QSIIG)
Geocentric Datum of Australia
Mapping Standards
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Australian Defence Forces adopted a
geocentric Datum in June 1992
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Aeronautical & Hydrographic
organisations will adopt GDA by 1998
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Dept. Natural Resources will adopt GDA
by mid 1998
Geocentric Datum of Australia
Technology Issues
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Commercialisation
of GPS
Changing nature of
the typical GPS
user
Diverse
applications
Future positioning
systems
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Impact of GIS
Breadth of GIS
applications
AM / FM
Fundamentals of
Corporate
Information
Management
Spatial Engines
Geocentric Datum of Australia
AGD
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Terrestrial
Observations
Systematic Errors
Constrained by
Doppler (transformed)
Distribution
Homogeneity
Location of Marks
Geocentric Datum of Australia
GDA
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GPS Observations
Small Random
Errors
Constrained by
GPS
Distribution
Homogeneity
Marks are
Accessible
Geocentric Datum of Australia
Ellipsoids and Geoids
Geocentric Datum
(best fit globally)
The Geoid
(Mean Sea Level)
Local Datum
AGD84
(best fits Australia)
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Geocentric Datum of Australia
Reference Frames
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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
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Geocentric Datum of Australia
Progress to Date

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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 Date
 100
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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 GDA
Readjust observations
constrained
to GDA coordinates
Readjustment
Coordinates Shift
Block Shifts
Coordinate Shifts;
Rotations and Scale
7 Parameter
Transformation
Coordinate Shifts;
Rotations and Scale
plus Distortion Model
Distortion
Model
{10
metres}
{2-3 metres}
{abt. 5 cm}
Geocentric Datum of Australia
Datum Transformation
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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
Z
Rz
Y
Ry
Dz
Dx
Dy
Rx
X
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Geocentric Datum of Australia
The Source of
these Distortions
abt. 5cm
2-3 metres
Shift determined from
7 Parameter Transformation
(most of 200m shift)
True GDA
Shift determined from
Distortion Modelling
(Most of what’s left)
abt.190 metres
True AGD
abt. 110 m
Geocentric Datum of Australia
Distortions between
Transformed AGD84 and GDA94
Western Qld
Central Coast
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Geocentric Datum of Australia
Coordinates Systems
and Projections
Z
N
X
f -X
l
Y
+Y
-Z
h
E
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Geocentric Datum of Australia
Coordinates Systems
and Projections
NMGA
NAMG
EAMG
EMGA
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Geocentric Datum of Australia
Universal Transverse
Mercator Projections
144o
147o
150o
Scale Factor
0.9996
ZONE 54
ZONE 55
6o wide zones
ZONE 56
Geocentric Datum of Australia
Effect of Ellipsoid Size and
Shape on Map Sheets
equator
GDA
AGD
difference in eastings
and northings
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Geocentric Datum of Australia
The Three Dimensional
Nature of GDA
Topography
h(AGD)
H(AHD)
Geoid (MSL)
h(GDA)
Ellipsoid (AGD)
N(AGD)
N(GDA)
Ellipsoid (GDA)
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Geocentric Datum of Australia
Implementation Plan
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January 1998
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July 1998
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Cabinet Endorsement; Methodologies;
Communication, Education.
Data sets; Standards; Pilots; Tools;
Communication.
July 1999
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Implementation; Support; Communication.
Geocentric Datum of Australia
Strategy
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Technical & Quality
Standards
Decision by your
Partners (clients
and data suppliers)
Accuracy &
reliability
Standards
Mapping Practices
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Technical
Competencies
Product Options
Presentation Issues
Software
Compatibility
Contractural Issues
Time Frames
Geocentric Datum of Australia
What is the Latest?
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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 Datum
of Australia
(GDA)
Peter Todd
Project Manager
GDA Implementation
Matt Higgins
Technical Manager
GDA Implementation
ICSM