Coordinates and CORSnet-NSW: Dealing with distortions in GDA94

CORSnet-NSW is a rapidly growing network of Global Navigation Satellite System (GNSS) Continuously Operating Reference Stations (CORS) providing fundamental positioning infrastructure for New South Wales now and into the future. Currently consisting of over 50 permanent stations tracking multiple satellite constellations, CORSnet-NSW will expand to over 70 stations within a year and plans are on the drawing board for the network to increase to nearly 120 stations shortly after that. For spatial professionals, the introduction of CORS or 'active' control marks will revolutionise positioning, but they must work in tandem with the traditional 'passive' marks in the ground. Issues arise for high-accuracy applications simply because the new control marks are far more accurate than the old. To solve these issues for GNSS users in NSW, we have introduced what some may see as a new realisation of the existing national horizontal datum. Others will argue these are only refined coordinates with superior Positional Uncertainty. Whatever your view, the geodetic experts at the NSW Land and Property Management Authority (LPMA) have dubbed this new horizontal system GDA94(2010). To avoid confusion, the original definition of GDA94 that people have been using for the last 15 years or so is referred to as GDA94(1997). Both will have to work in tandem for a few more years. This article helps explain the reasoning behind this introduction and outlines how the new realisation should be dealt with in practice, in the field.