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VicRoads and “Pseudo AMG”

Recently I was attempting to import some data sourced from VicRoads, but had a huge struggle trying to find the correct coordinate system to plot it in. The data had columns labelled amg_x and amg_y, so naturally I assumed this referred to either AMG66 zone 54 or 55. Neither of these fit though – the points were plotting about 200km out from their correct location.

It turns out VicRoads “helpfully” uses their own coordinate system, Pseudo AMG (described on pages 18 & 19 in this document). If you’re trying to import this data into a modern GIS, this coordinate system can be described by the proj string:

+proj=tmerc +lat_0=0 +lon_0=145 +k=1 +x_0=500000 +y_0=10000000 +ellps=WGS84
+towgs84=-117.808,-51.536,137.784,0.303,0.446,0.234,-0.29 +units=m +no_defs

With any luck this may save someone else the time I spent trying to mangle this data into shape. Thanks VicRoads… ThicRoads.

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