4

I've been asked to recommend a mapping coordinate reference frame for use for Australian mapping, which I've said AHD for the vertical component and GDA94 for the the horizontal component.

However, I'm not sure whether they cover all the islands/territories around Australia.

For islands that are not closely adjacent, but are nevertheless administratively part of Australia (e.g Christmas, Lord Howe, and Norfolk islands) what would they use if not the same as Australia?

4

The subcommittee that maintains the EPSG Geodetic Registry briefly had an Australian member who got some of the Australian data updated. Even so, these may not be the current coordinate reference systems.

Christmas Island

Currently the GeodCRS is GDA94 while the ProjCRS is GDA94 / CIG94. WKT (in the new format) is:

PROJCRS["GDA94 / CIG94",
  BASEGEODCRS["GDA94",
    DATUM["Geocentric Datum of Australia 1994",
      ELLIPSOID["GRS 1980",6378137,298.257222101,LENGTHUNIT["metre",1.0]]]],
  CONVERSION["Christmas Island Grid 1994",
    METHOD["Transverse Mercator",ID["EPSG",9807]],
    PARAMETER["Latitude of natural origin",0,ANGLEUNIT["degree",0.01745329252]],
    PARAMETER["Longitude of natural origin",105.625,ANGLEUNIT["degree",0.01745329252]],
    PARAMETER["Scale factor at natural origin",1.00002514,SCALEUNIT["unity",1.0]],
    PARAMETER["False easting",50000,LENGTHUNIT["metre",1.0]],
    PARAMETER["False northing",1300000,LENGTHUNIT["metre",1.0]]],
  CS[cartesian,2],
    AXIS["easting (E)",east,ORDER[1]],
    AXIS["northing (N)",north,ORDER[2]],
    LENGTHUNIT["metre",1.0],
  ID["EPSG",6721]]

Norfolk Island

GDA94 / MGA zone 58 for onshore/offshore west of 168E and GDA94 / MGA zone 59 for offshore east of 168E

Lord Howe Island

GDA94 / MGA zone 57.

Disclosure: I'm on the subcommittee.

2

Since you are making the recommendation, I think you need to become familiar with these and other Geoscience Australia pages related to Geodetic Datums, if you are not already:

The Geocentric Datum of Australia (GDA) is the latest Australian coordinate system, replacing the Australian Geodetic Datum (AGD).

If the levels on islands closely adjacent to the Australian mainland are observed to standard third order accuracy, and are referred to mean sea level at a satisfactory tide gauge, they are deemed to be part of the Australian Height Datum.

  • Thanks for the reply, I am familiar with the GDA and AHD pages but will check out the other geodetic datums page aswell. For islands that are not closely adjacent; e.g Christmas, Lord Howe, and Norfolk islands what would they use if not the same as Australia which I think they would, but I can't find a definitive answer anywhere – Alex Hunter Oct 14 '15 at 5:21
  • I think those specific details would make a useful edit to your question. Being new to GIS SE, I recommend that you take the Tour to see how our focussed Q&A format operates. – PolyGeo Oct 14 '15 at 5:48

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