Geographic coordinate system

A geographic coordinate system (GCS) is a coordinate system which uses a three-dimensional spherical surface (ellipsoid) to define locations on the earth. The WGS84 coordinate system belongs to this category. A common choice of coordinates is latitude, longitude and elevation. Basically, a GCS is used to define your real-world points on a 3-dimensional digital surface.

A Geographic Coordinates System is constituted by a datum (DATUM), a prime meridian (PRIMEM) and unit (UNIT). The datum is constituted by a ellipsoid model (SPHEROID) and a anchor point.

Projected coordinate system

In a Projected Coordinate system (PCS) you project the geographic coordinate (GCS) that you have measured to for example a cylinder which you roll out easily on two-dimensional surface (the map). There exist many different projections and we'll not go in further detail about that here. 

Typically every country, state or region has its optimal projected coordinate system which minimizes distortions for particular applications like mapping

Examples are:

  • South central Texas in the United States uses "NAD83( NSRS2007) / Texas South Central (ftUS)" with unique EPSG code 3674
  • Belgium uses "ETRS89 / Lambert 2008" with unique EPSG code 3812

A projected coordinate system is constituted by a geographic coordinate system from which it's project (GEOGCS) and other projection parameters like the measurment unit (UNIT) like meter or US Survey Foot), the projection and its project parameters.

The coordinate system is usually stored in the input file (GeoTIFF) and is read automatically when you create a terrain in Virtual Surveyor. The text marked in yellow below is the projected coordinate system applicable to the input orthophoto. The number following the coordinate system is the EPSG code.

Example of a Projected Coordinate System in Virtual Surveyor

Example of a Geographic Coordinate System in Virtual Surveyor