Project Zones

Document No:  D12#434761
Revision:  6
Date amended:  15-Nov-2019

The information below is intended to reflect the preferred practice of Main Roads Western Australia ("Main Roads"). Main Roads reserves the right to update this information at any time without notice. If you have any questions or comments please contact Rod Stone  by e-mail or on (08) 9323-6381. 

To the extent permitted by law, Main Roads, its employees, agents, authors and contributors are not liable for any loss resulting from any action taken or reliance made by you on the information herein displayed.

Revision Register


Ed/Version Number Clause Number Description of Revision Date
 1 All Guideline Developed  06-Dec-2002 
 2 All Changed to Ownership and Chapter 6 24-Apr-2007 
 2A Header Contact Person changed. 05-Mar-2009 
​3 ​All ​Content Cleanup ​5-Feb-2013
​4 ​Header ​Document Number Changed ​16-Jun-2014
​5​All​Guideline Review​10-May-2017
​6​Header​Updated contact​15-Nov-2019

Table of Content

1 Background

In the Surveying and Mapping industry, developments in the acquisition, use, manipulation and analysis of digital data has placed an emphasis on the requirement for a common reference base for all data.  The integrity and interchange of such data has become totally reliant upon data users adopting a common reference system.

The densification of the Geodetic network across Australia has provided the framework for this common base, the Geocentric Datum of Australia 1994 (GDA 94) or Australian Geodetic Datum 1984 (AGD 84).

Engineering projects are predominantly designed using the modelling techniques associated with Computer Aided Design which use a vast quantity of digital data obtained from a number of sources e.g. survey, photogrammetric mapping, cadastral and utilities.  The GDA 94/AGD 84 is ideally suited to mapping applications, however there are serious limitations when adopted for engineering applications. This is because GDA 94/ AGD 84 rarely maintains the ground measurement to plan measurement relationship.  In other words designing on the GDA 94/AGD 84 would mean designing on a spherical plan and not on the 'flat ground'.  This situation would further complicate the construction set out phase of the project by introducing scale factors to all measured distances and more importantly the design dimensions.  

In order to overcome this situation Plane Project Coordinate Systems are generally adopted by most engineering agencies.  Many types of plane coordinate systems have been utilised which are generally very localised and use approximations requiring the least complicated computing solution.  The proliferation of project coordinate systems, even on occasions by different organisations operating within the same project has continued to be a problem.  Data interchange between agencies has been unnecessarily complex with little data ever being transformed back to the standard GDA 94/AGD 84 base, if at all possible.

2 Project Co-ordinate Systems In Main Roads

The policy adopted by Main Roads is that GDA 94/AGD 84 will be adopted as the reference base for all its Geodetic and Mapping applications.  However designers undertaking work on engineering projects should not be concerned with the intricacies of the GDA 94/AGD 84 and should simply supply and work with data in Main Roads Project Zone co-ordinates only. 

It is important to understand that Project Zones created on GDA 94 and AGD 84 are different and should not be confused.  All GDA 94 project zones have "94" at the end of their name.  eg PCG 94 is the GDA 94 project zones where as PCG is the AGD 84 project zone.

3 Major Benefits of Project Zones

  • Geographical Coordinates (latitude and longitude) do not change.
  • Existing conversion software from grid coordinates to geographics and reverse, including Zone to Zone routines can still be utilised, the only change being the zone parameters themselves. 
  • Where rigorous solutions are required the Project Zone can be used as a non standard UTM zone.
  • Within the accepted 20ppm accuracy limits, provides a standard Plane Coordinate system over the whole project (ie plan distance equals ground distance).
  • Provides a standard for the interchange of data within the engineering and survey and mapping industry.

4 Project Zone Parameters

For Main Roads projects the following five parameters are required for rigorous transformations between GDA 94/ AGD 84 and Project Zone and vice versa. 

Central Meridian
The longitude of the project zone is generally centrally located within the bounds of the project zone.

False Easting
In most instances a standard false easting of 50,000m is used to avoid using negative numbers.

False Northing
Is calculated by the latitude at the centre of the project zone.  The number selected will avoid negative numbers.

Central Scale Factor
Is the relationship between the height above spheroid (HAS) and the radius of the Earth.

Radius of the Earth
GDA 94 Radius of Earth - 6,364, 400 m

AGD 84 Radius of Earth - 6,366,000 m

Example of an AGD 84 determined Central Scale Factor

From studying 1:100 000 map sheets over a project area the average height (h) is determined to be 500 m (this includes the geoid-spheroid separation). 

Using R=6,366,000m in the formula R+h the uncorrected CSF is 1.000078542.

The corrected CSF is 1.000079, which using the formula in reverse, gives a HAS value of 502.914m.  This latter value is adopted as HAS for the Project Zone. 

5 Transformation Accuracy

As Main Roads projects regularly cover large areas the accuracy of the GDA 94/ AGD 84 - Project coordinate transformation is all important.  In selecting a transformation method the following features are desirable:

  • Maximum allowable error less than 20 ppm
  • 50 kilometre east/west coverage
  • Rigorous GDA 94/ AGD 84/Plane transformation (i.e. reversible)
  • Compensate for height above the reference ellipsoid

The transformation accuracy is the difference between the plane distance calculated from project coordinates and the true ground distance.  As a general rule 1:50 000 or 20 ppm has been set as desirable to avoid measurable differences in survey control. 

The accuracy of the project coordinate transformation is a function of both distance from the project Central Meridian and deviation from the chosen mean terrain height.

6 Survey Portal/Project Zones

The Survey Portal provides direct access to view Main Roads Project Zones on line via a graphical interface.  The site, developed by the Survey and Mapping Section, allows the user to identify the correct Project Zone for a Main Roads project and then view or print out the required parameters.  To assist the user to select the correct Project Zone, various backgrounds including the road network, towns, regions and/or the Travellers Atlas can be viewed and interrogated.

Sample GDA 94 Project Zone Summary Sheet

Sample AGD 84 Project Zone Summary Sheet

Project Zone Presentation (PDF 420KB)