Coordinate Reference Systems

Geodesy is a very extensive subject; therefore this document will not attempt to cover all the different aspects of coordinate reference systems. Anyone interested in a more comprehensive discussion of geodesy can refer to the many books and articles on the subject that are readily available on the internet.

However, it is important for the layman to understand that a set of coordinates (whether it be latitude and longitude or easting and northing) has no meaning without reference to a known Coordinate Reference System (CRS).  When giving the coordinates of a location in latitude and longitude, for example, we also need to specify the geodetic datum on which the geographic coordinates are based, e.g. GDA94 or AGD84. When providing easting and northing, we typically need to qualify this by adding the UTM zone for the map projection, e.g. UTM 51 South.

Consequently, all spatial coordinates stored in the OCRIS database are linked to a coordinate reference system, or CoordSys for short. The ODBT makes use of a CoordSys code that encapsulates all the geodetic metadata that may be required to correctly interpret the spatial context of the set of coordinates. These metadata can be used to calculate a comprehensive coordinate suite, comprising both geographic and projected coordinates, as shown in the following table.

Project	SiteID	CoordSys	GridUTM	EastingUTM	NorthingUTM	Datum	Latitude	Longitude
MTREEW	WV019	MGA94-51	UTM51S	552813	6285486	GDA94	-33.569	123.56903
MTREEW	WV024	MGA94-51	UTM51S	553043	6284577	GDA94	-33.5772	123.57156
MTREEW	WV025	MGA94-51	UTM51S	553298	6283631	GDA94	-33.5857	123.57437

The definition and management of these codes is an administrative task that will be discussed later.