Co-ordinates on the ACT Standard Grid are derived from a Transverse Mercator projection of geographic co-ordinates on the AGD66.

They are defined by the formulae for easting and northing as given in The Australian Geodetic Datum Technical Manual, Special Publication No 10 (SP 10) of the National Mapping Council 1986 Chapter 4, "Rigorous Formulae between Spheroid and Grid". They are also commonly referred to as "Redfearn's Formulae".

Parameters for the ACT Standard Grid

Ellipsoid is the Australian National Spheroid (ANS)

Major semi-axis (a) = 6,378,160 metres

Flattening (f) = 1/298.25 exactly

Additional quantities that may be required

Minor semi-axis (b) = 6,356,774.719 metres

Eccentricity² (e²) = 0.006 694 541 855

Second eccentricity² (e´²) = 0.006 739 660 796

Meridian of Origin is Mt Stromlo Trig Station: 149º 00' 33".46139 East

Latitude of Origin is the Equator: 0º

Latitude of Mt Stromlo Trig: 35º 19' 03".85060 South

Scale Factor (k0) at Central Meridian (CM) = 1.000 086

Zone Width: As the projection has only one zone, this quantity is discretionary, but preferably should be restricted so as to contain the E-W extents of the Australian Capital Territory.

Meridian Distance

The meridian distance (m) from the equator to Mt Stromlo Trig along the line of longitude at "sea level" = 3,909,857.2463 metres. It is calculated using the expression given in paragraph 4.3 of the abovementioned SP10 document.

The distance (mk0) from the Equator to the False Origin for Northings, that is, a point 600,000 metres south of Mt Stromlo Trig, is comprised of the true distance from the Equator to Mt Stromlo Trig, multiplied by the above Combined Scale Factor (k0).

(3,909,857.2463 x 1.000 086) + 600,000.000 = 4,510,193.494 metres. This is the quantity that is used as the "False Northing" for software development.

The False Easting is 200,000.000 metres.

ACT Standard Grid Co-ordinates of Mt Stromlo Trig

E 200,000.000 metres

N 600,000.000 metres

For further information on the development of this projection, refer to:

Wellspring, K. H. "Some Aspects of the Conversion from Imperial to Metric Co-ordinates in the Australian Capital Territory", Surveying & Mapping Australia. (Technical paper presented at the 16th Australian Survey Congress, Canberra 1973).

Converting AGD66 Co-ordinates to GDA94 and vice versa

Current Bursa-Wolf (3D Helmert, etc) parameters (3D) for transformations between GDA94 and AGD66 as realised in the ACT are:

AGD66 to GDA94 GDA94 to AGD66 GDA94 to AGD66 AGD66 to GDA94
Dx=  -131.017m Dx=  131.017m
Dy=  - 39.798m Dy=   39.798m
Dz=   129.552m Dz=  -129.552m
Rx=  -0.225” Rx=   0.225”
Ry=  -0.373” Ry=   0.373”
Rz=  -0.327” Rz=   0.327”
Scale=  -3.356 ppm Scale=   3.356 ppm