Policy No: 67/08/25
MAIN ROADS POLICY
for
Co-ordinate Systems
POLICYThe 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 1July2000 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
MAIN ROADS POLICY
for
Co-ordinate Systems
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 July12000. Project/Branch Managers should use GDA 94 for all new projects commencing March302000. 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 July12000 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 GDA94:
· What spatially referenced data do you currently control that will be used after July12000?
· 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.
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 AttachmentII.
MAIN ROADS POLICY
for
Co-ordinate Systems
2. PROCEDURE
Does your spatially referenced data require transformation?
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 GDA94 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
D
X = -128.5
DY = -53.0
DZ = 153.4
Da = -23
Df = -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
DX = -117.763
DY = -51.510
DZ = 139.061
RX = -0.292
RY = -0.443
RZ = -0.277
l = -0.191
(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
MAIN ROADS POLICY
for
Co-ordinate Systems
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 co-ordinate 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.
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. A change in the origin of the reference ellipsoid from ANS (Australian centred)
to GRS80 (earth centred) (change is »200 metres).
2. 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 / AFTER DECEMBER 4 2000Australian Geodetic Datum 1984 / Geocentric Datum of Australia 1994
Australian National Spheroid / Geodetic Reference System 1980
Australian Map Grid 1984 / Map Grid of Australia 1994
The table below shows the effect of a 200 metre shift at various map scales.
MAP SCALE / SHIFT1:1,000 / 200.0mm
1:5,000 / 40.0mm
1:10,000 / 20.0mm
1:25,000 / 8.0mm
1:50,000 / 4.0mm
1:100,000 / 2.0mm
1:250,000 / 0.8mm
Approximate coordinate shift from AGD 84 to GDA 94(in metres) across Australia
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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Sample Project Zone Summary Sheet
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Sample Meta Data Statement
Metadata Category / Core Metadata Element / DescriptionDataset / Title / Metropolitan Road Centreline Network
Custodian / Main Roads Western Australia
Contact Address / Contact Organisation / Survey and Mapping Section - Main Roads Western Australia
Contact Position / Senior Geodetic Surveyor
Mail Address / PO Box 6202
East Perth Western Australia 6892
Telephone / (08) 9323 4152
Facsimile / (08) 9323 4449
Electronic Mail /
Description / Abstract / Road centrelines for all classified (main) and unclassified (local) roads in the Perth Metropolitan area
Keywords / Road, centreline, road name
Geographic Extent / -31.4553, 115.5811
-31.4618, 116.4157
-32.4672, 115.5654
-32.4740, 116.4092
Dataset Currency / Beginning Date / 13/01/1992
Ending Date / 30/04/1997
Dataset Status / Progress / Complete
Maintenance and
Update Frequency / Annual
Access / Native Dataset Format / Digital - vector (ARC/INFO)
Available Format
Types / Digital - ARC/INFO
Digital - Design File
Digital - ASCII
Digital - DXF
Access Constraints / Restricted Access (License)
Data Quality / Lineage / 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
Positional Accuracy / 1 - 3 metres
3 - 5 metres for updates using 1994 digitised DOLA cadastre
Attribute Accuracy / 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.
Logical Consistency / Digital data has been visually verified against Main Roads’ State of Construction plans and metropolitan street directories.
Completeness / 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.)
Metadata Date / Metadata Date / 30/04/1997
Further Information / Further Information / WALIS
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