Planning and Practice Directorate
Road and Traffic Engineering Branch
Policy No: 67/08/25
MAIN ROADS POLICY
for
Co-ordinate Systems
POLICY
The geodetic datum adopted for all spatially referenced data is
the existing Australian Geodetic Datum 1984 (AGD 84) or
an approved AGD 84 Project Zone.
As of 1 July 2000 the geodetic datum to be adopted by Main Roads Western
Australia will be the Geocentric Datum of Australia 1994 (GDA 94) or
an approved GDA 94 Project Zone.
CONTENTS
PAGE
1.
GUIDELINES ...................................................................................................................................... 2
2.
PROCEDURE ...................................................................................................................................... 4
3.
STANDARDS....................................................................................................................................... 5
4.
NOTES ................................................................................................................................................. 7
Authorisation
……………………………
EXECUTIVE DIRECTOR PLANNING AND PRACTICE
DATE: ……………………
All Controlled Copies shall be marked accordingly
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MAIN ROADS POLICY
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1.
GUIDELINES
1.1
General
GDA 94 is the new Australian co-ordinate system for spatially referenced data and will
replace AGD 84 as the standard co-ordinate system for Main Roads WA.
Main Roads WA will adopt GDA 94 for all spatially referenced projects as of
July 1 2000. Project/Branch Managers should use GDA 94 for all new projects
commencing March 30 2000. Existing spatially referenced projects shall be completed
on the existing AMG 84 co-ordinate system and at the completion of the project relevant
corporate data shall be transformed to GDA 94.
1.2
Transformation of Spatially Referenced Data
Existing corporate datasets that are spatially referenced and will be used after July 1 2000
need to be transformed to GDA 94.
Spatially referenced projects are those projects connected to a co-ordinate system. Some
examples of spatially referenced projects include:







Road designs
Road centrelines
Survey data
Environmental sites
Material locations
Cadastral data
Hand held GPS locations
The following issues should be considered when determining the need to transform
existing spatially referenced data to GDA 94:



What spatially referenced data do you currently control that will be used after
July 1 2000?
What is the accuracy of the data sets? <1 m, 2 m or >5 m?
What software do you operate that uses spatially referenced data or systems?
Microstation, Moss or CSV?
Additional information regarding GDA 94 transformations can be sought by contacting
the Senior Geodetic Surveyor.
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1.3
Project Zones
Project Zones will be affected by the introduction of GDA 94. New GDA 94 Project
Zones can be obtained by contacting the Senior Geodetic Surveyor.
Refer to section 4.3 for a full explanation regarding the use of Project Zones.
1.4
Use of the GDA 94 Logo
To distinguish between the different geodetic datums used, all GDA 94 products, (both
digital and hard copy) must display the GDA 94 logo below and meta data statements are
to be attached with all spatially referenced information that is sourced or supplied. A
copy of the logo is displayed below and a meta data statement can be seen at
Attachment II.
MAIN ROADS Western Australia
Co-ordinate Systems Policy
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MAIN ROADS POLICY
for
Co-ordinate Systems
2.
PROCEDURE
Does your spatially referenced data require transformation?
List existing spatially referenced data
you currently control
No
Is this data
required for
use after
July 1 2000?
Yes
What is the data accuracy?
What format is the data in?
Senior Geodetic Surveyor to advise the
most appropriate method of
transformation for the data set.
Data in correct
co-ordinate
system
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Co-ordinate Systems Policy
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MAIN ROADS POLICY
for
Co-ordinate Systems
3.
STANDARDS
3.1
Transformation Methods for Digital Data
There are four major transformation methods available to transform existing AGD 84 to
GDA 94 and vice versa for digital data. Advice can be sought from the Senior Geodetic
Surveyor as to the most appropriate transformation for your existing data.
(i)
Block Shift Method: This is the simplest technique to transform spatially related
data. This method requires a common series of points in both co-ordinate systems
and from these an average value is derived.
Transformation accuracy is around 20m.
(ii)
3 Parameter Molodensky Transformation: This is a mathematical model
transformation that calculates average transformation shifts in X, Y and Z. Most
generic spatially referenced software should be capable of this computation.
Transformation accuracy is around 2 m.
3 Parameter Molodensky Transformation Values
X = -128.5
Y = -53.0
Z = 153.4
a = -23
f = -0.00000008119
(iii)
7 Parameter Similarity Transformation: This is similar to the 3 Parameter
Molodensky Transformation but not only uses shifts in X, Y and Z but also
computes for rotations of the axis and a scale change. Again, most generic
spatially referenced software should be capable of this computation.
Transformation accuracy should be less than 2 m.
7 Parameter Similarity Transformation Values
X = -117.763
Y = -51.510
Z = 139.061
RX = -0.292
RY = -0.443
RZ = -0.277
 = -0.191
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(iv)
Grid File Technique: This method of transformation will provide the optimum
solution and undertakes distortion modelling techniques from data within the Grid
File. The file will be available by March 2000.
Transformation accuracy will be 2 – 5 cm
3.2
Universal Transverse Mercator Projection Parameters
The existing zone coverage throughout the state will remain unchanged and the
applicable zones will still be 49, 50, 51 and 52. The following parameters apply
for the Universal Transverse Mercator (UTM) projections




6o wide zones
Central Scale Factor 0.9996
False Easting 500,000 m
False Northing 10,000,000 m
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MAIN ROADS POLICY
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4.
NOTES
4.1
General
The Geocentric Datum of Australia 1994 (GDA 94) is the new Australian co-ordinate
system, replacing the Australian Geodetic Datum (AGD). GDA 94 is part of a global coordinate reference frame and is directly compatible with the Global Positioning Systems
(GPS).
On June 4 1996 the Western Australian Cabinet approved the adoption of the Geocentric
Datum of Australia by 1 January 2000. However, this date has now been amended and
implementation will occur by December 4 2000. All government agencies are responsible
for their own implementation as determined by Cabinet.
The Western Australian Land Information System (WALIS) Council has been made
responsible for the oversight and introduction into Western Australia of the Geocentric
Datum of Australia 1994. The Department of Land Administration (DOLA) was made
responsible for all technical issues associated with the introduction of GDA 94.
The Senior Geodetic Surveyor will be responsible for the co-ordination and
implementation of GDA 94 within Main Road Western Australia.
AGD and GDA 94 are two different mathematical models of the shape of the Earth.
Each has a different origin and subsequently a point on the Earth's Surface will have
different co-ordinates based on each datum.
Earth Centred GDA 94
Australian Centred AMG 84
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GDA 94 will vary by about 200m in a north easterly direction from AGD coordinates
because of the different reference datums. The actual size and orientation of the change
will vary slightly from place to place. There will be two major outcomes as a result of
the introduction of GDA 94:
1.
2.
A change in the origin of the reference ellipsoid from ANS (Australian centred)
to GRS80 (earth centred) (change is 200 metres).
The upgrading and readjustment of the Australian Geodetic Network with new
and more accurate survey measurements (change is 0-2 metres).
The Australian Height Datum (AHD) will not be affected by the adoption of GDA.
With the introduction of GDA 94 the following naming conventions will apply:
BEFORE DECEMBER 4 2000
Australian Geodetic Datum 1984
Australian National Spheroid
Australian Map Grid 1984
AFTER DECEMBER 4 2000
Geocentric Datum of Australia 1994
Geodetic Reference System 1980
Map Grid of Australia 1994
The table below shows the effect of a 200 metre shift at various map scales.
MAP SCALE
1:1,000
1:5,000
1:10,000
1:25,000
1:50,000
1:100,000
1:250,000
SHIFT
200.0mm
40.0mm
20.0mm
8.0mm
4.0mm
2.0mm
0.8mm
Approximate coordinate shift from AGD 84
to GDA 94(in metres) across Australia
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4.2
Use of Handheld GPS Units
All handheld GPS receivers will facilitate GDA 94 co-ordinates. This is possible with
older model handheld GPS units using the World Geodetic System 1984 (WGS 84) as the
reference datum/spheroid which, for all practical purposes can be considered identical to
GDA 94.
When using handheld GPS units as a navigation aid, users will need to be aware of which
co-ordinate reference system they are working with. This information can be found in the
meta data statement of the hard copy maps, and the GPS reference datum/spheroid must
be altered accordingly.
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4.3
Project Zones
Although the AMG 84 and GDA 94 reference systems are the basis for correlating
spatially referenced data sets, the actual ground to plan measurements are rarely the same.
For Main Roads applications this situation complicates both the design and construction
setout phase by introducing scale factors to all measured ground distances and design
dimensions.
To facilitate the interchange of data and provide a common coordinate base that will
enable flat surface calculations on a spherical earth, Main Roads has found it necessary to
standardise on a transformation system that directly relates to AMG 84 or GDA 94.
The establishment and use of Project Zones allows rigorous transformations to be
performed between AMG 84, GDA 94 and Project Zones.
To enable the Senior Geodetic Surveyor to establish, maintain or check the adequacy of
Project Zones define the project extremities by supplying the road name, start and finish
Straight Line Kilometres (SLKs) and a location in relation to a town.
The Senior Geodetic Surveyor can also facilitate the transformation of existing data from
AGD 84 or GDA 94 to an approved project zone.
Refer to Attachment I for an example of a Project Zone Summary Sheet.
4.4
Meta Data Statements
A Meta Data Statement shall accompany all data sourced and supplied to the Main Roads
Western Australia. The Meta Data statement shall contain a description of the data, its
source, currency and accuracy statements
Refer to attachment II for a sample meta data statement
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ATTACHMENT I
Sample Project Zone Summary Sheet
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ATTACHMENT II
Sample Meta Data Statement
Metadata
Category
Dataset
Contact Address
Description
Core Metadata
Element
Title
Custodian
Contact Organisation
Contact Position
Mail Address
Telephone
Facsimile
Electronic Mail
Abstract
Keywords
Geographic Extent
Dataset Currency
Dataset Status
Access
Data Quality
Beginning Date
Ending Date
Progress
Maintenance and
Update Frequency
Native Dataset Format
Available Format
Types
Access Constraints
Lineage
Positional Accuracy
Attribute Accuracy
Logical Consistency
Completeness
Metadata Date
Further
Information
Metadata Date
Further Information
Description
Metropolitan Road Centreline Network
Main Roads Western Australia
Survey and Mapping Section - Main Roads Western Australia
Senior Geodetic Surveyor
PO Box 6202
East Perth Western Australia 6892
(08) 9323 4152
(08) 9323 4449
geoff.xanthis@mrwa.wa.gov.au
Road centrelines for all classified (main) and unclassified
(local) roads in the Perth Metropolitan area
Road, centreline, road name
-31.4553, 115.5811
-31.4618, 116.4157
-32.4672, 115.5654
-32.4740, 116.4092
13/01/1992
30/04/1997
Complete
Annual
Digital - vector (ARC/INFO)
Digital - ARC/INFO
Digital - Design File
Digital - ASCII
Digital - DXF
Restricted Access (License)
Original dataset compiled Jan 1992 using standard
photogrammetric procedures from 1:40 000 b/w aerial
photography.
Annual updates compiled from various sources including:
DOLA digital cadastral information Scanned aerial
photography
Field measurements
Design information
1 - 3 metres
3 - 5 metres for updates using 1994 digitised DOLA cadastre
Road centreline is a notional reference line that generalises and
approximates the centre of the pavement extent.
Road numbers have been verified against existing internal
corporate databases. Road names are currently undergoing
verification with Geonoma.
Contact custodian for technical capture specification.
Digital data has been visually verified against Main Roads’
State of Construction plans and metropolitan street directories.
Dataset contains all road centrelines in the Perth metropolitan
area at the time of the update photography. Private roads,
driveways etc. are not captured.
Contact custodian for centreline generalisation criteria (dual
carriageways, roundabouts, culs de sac etc.)
30/04/1997
WALIS
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