Remember your GPS may show locations as 200m different if the map is not based on the GDA. If it is not present, check the datum used. Look for the GDA logo on your topographic map. WGS84 is the most common default datum in GPS.Ī major implication of this change is that GDA coordinates (latitude and longitudes and eastings and northings) differ from their AGD predecessors by approximately 200 metres in a north-easterly direction. For the most practical navigation purposes WGS84 and GDA coordinates may be regarded as being the same. The primary reason for this change is the widespread use of satellite-based navigation systems such as the Global Positioning System (GPS), which is based on the geocentric datum known as the World Geocentric System 1984 (WGS84). This new datum was defined in 1994, and is based on a mathematical surface that best fits the shape of the earth as a whole, with its origin at the earth’s centre of mass, hence the term ‘geocentric’. The AGD84 coordinates are based on the same datum as AGD66 and for map reading and navigation purposes can be regarded as the same.įrom the year 2000, all Australian mapping authorities are using a new datum, the Geocentric Datum of Australia (GDA). In 1984 some Australian States adopted an updated version of this datum, known as AGD84. This datum best fitted the shape of the Earth for the Australian mainland. In 1966 the Australian Geodetic Datum (AGD) was defined. Mapping and coordinate systems are based on a datum, which is a mathematical surface that best fits the shape of the Earth. Vertical distance between contour lines on that particular map ![]() Method of indicating the scale of the map Gives the title and number of adjoining maps Gives map production details including the reliability, grid(s) shown, datums adopted Gives a legend of the symbols used on the map to represent various features, together with their meanings Shows, for a given year, the relationship between true, magnetic and grid north and their variations from grid north over time Identifies the map edition and the map numbering system (map number)ĭescribes how to determine a six figure grid reference * See ChangeLog for information on the currently implemented releases of NADCON and VERTCON.It may be the name of an important town or an area and indicates roughly the location of the mapĭescribes the type of map, e.g. Orthometric Height Height Transformations (VERTCON).Latitude,Longitude,and Ellipsoid Height Transformations (NADCON).State Plane Coordinates, NAD 27 (GPPCGP 2.0).State Plane Coordinates, NAD 83 (SPC83 2.1).Universal Transverse Mercator Coordinates (UTMS 2.1).NCAT incorporates the capabilities of the following NGS computer programs, which originally were stand-alone products: Only orthometric-to-orthometric and ellipsoidal-to-ellipsoidal height transformations are currently possible in NCAT. ![]() Please note that, although either orthometric or ellipsoidal heights can be used as inputs to NCAT, at this time NCAT does not convert between orthometric and ellipsoidal heights. NADCON and VERTCON provide local error estimates for each transformation, and do not support transformations which are outside the boundaries of the supported areas (generally, CONUS, Alaska, Hawaii, Puerto Rico and the US Virgin Islands, American Samoa, and Guam and Northern Mariana Islands). Transformations are provided for a wide range of frames/datums and regions in the National Spatial Reference System. NCAT currently uses NADCON* to perform three-dimensional (latitude, longitude, ellipsoid height) coordinate transformations and VERTCON* to perform orthometric height transformations. ![]() For coordinate conversion, NCAT allows conversion between lat/long/height, SPC, UTM, XYZ, and USNG systems. NGS Coordinate Conversion and Transformation Tool (NCAT) allows users to easily convert between different coordinate systems and/or transform between different reference frames and/or datums, in a single step.
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