This tutorial explores the various geographic and projection coordinate systems used within Australia. It explores the latest datum, known as the Geocentric Datum of Australia 2020 (GDA2020), and how it differs to its predecessor. Finally, it will discuss the concept of a Project Local coordinate to eliminate rounding errors and graphical limitations in non-GIS enabled software, such as Revit.
Geographic Coordinate System
A Geographic Coordinate System (GCS) uses a three-dimensional spherical surface to define locations on the earth. It includes an angular unit of measure, a prime meridian, and a datum (based on a spheroid). In a geographic coordinate system, a point is referenced by its latitude and longitude values (reference). Sydney for example has a latitude of 33.877° S and a longitude of 151.215° E.
While a spheroid approximates the shape of the earth, a datum defines the position of the spheroid relative to the centre of the earth. In the last 15…