What is happening?
The Australian national mapping authorities have decided to replace their national datum (GDA94) with a new one (GDA2020). These datums define the relationship between positions on Earth and numeric coordinates (typically latitude, longitude, and ellipsoid height) before any formulas are applied to flatten things out for 2D maps. There are two main reasons a national datum would be replaced: increased accuracy available from new technologies and growing inconsistency vs. GPS due to earthquakes and drifting tectonic plates; these are all in play here.
What it means for our users
As GDA2020 becomes law, positions in Australia will increasingly be required and provided in terms of GDA2020 instead of GDA94. The differences are significant, with horizontal coordinates changing by about 1.8m. This means users (together with their software) will be required to correctly identify the coordinate system used by their input and output data, and correctly convert data in GDA94 to a reasonable GDA2020 equivalent. As above, any mistakes in this area risk distorting data by about 1.8m.
Converting existing data
Two techniques have been provided for converting GDA94 coordinates to GDA2020 ones:
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A conformal transform. This was released in the "Geocentric Datum of Australia 2020 Interim Release Note" in early March, 2017. It was initially provided as a similarity transformation, and is now also available as an equivalent NTv2-format grid. (We don’t include this grid with FME as it’s much larger than the parameter-based version, and yields the same results.)
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A combined conformal and distortion transform. This was released as an NTv2-format grid in December 2017.
We expected that a single NTv2-format grid would be provided, and that it would be preferable to the similarity transform in almost all cases; what actually happened is a bit more complicated. It turns out the appropriate choice of transformation (conformal vs. conformal and distortion) depends on both how the data was gathered, and in which jurisdiction it was gathered in. Users are advised to consult the Geocentric Datum of Australia 2020 Technical Manual for details. (In Version 1.3, the relevant portions include Section 3.7.1 and Table 3.4.)
What we have done
As of FME 2017.1 we have made the following updates:
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Defined coordinate systems in FME corresponding to the GDA2020 coordinate systems recently added to EPSG.
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Defined a transformation between the GDA94 and GDA2020 datums based on the similarity transform.
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Defined mappings between these coordinate systems and the GIS application formats we support which also support GDA2020 in their latest versions.
As of FME 2018.0, we have added the NTv2 grid transformation to FME. In the initial 2018.0 beta build, the transformation names were GDA94_to_GDA2020_FME and GDA94_to_GDA2020_NTv2_Grid_FME, but we've renamed these to more explicitly denote the conformal vs. conformal-and-distortion distinction: GDA94_to_GDA2020_conformal_only_7P_FME and GDA94_to_GDA2020_conformal_and_distortion_NTv2_Grid_FME. (For those who jumped on the first beta, we’ll make sure your workspaces continue to work.)