About Geodesy

OpenWells® Software Features

Geodesy is the science of measuring the earth's surface. The earth is round and maps are flat. A geodetic system enables us to convert geodetic coordinates (angles on a round earth - latitude / longitude) to map coordinates (distances on a flat map - eastings / northings). To do this we must know the geodetic system, datum and zone.

Geodetic System

A geodetic system is one or more map projections covering adjacent parts of the globe. A system may comprise one or more zones. If you do not know the geodetic system, Flat Earth can be selected.

Geodetic Datum

A geodetic datum defines a common reference and shape for the surface of the earth in the area of interest. The datum is a definition of the center of the earth based on a common center (average). An ellipsoid is associated with a datum and is a definition of the radius of the earth and its eccentricity. The ellipsoid defines a geometric shape like an American football or rugby ball.

Geodetic Zone

A geodetic zone is one segment of a geodetic system. A geodetic system may contain several zones with each zone mapping a different area. As an example, let's look at three of the geodetic systems shipped with OpenWells software.

Universal Transverse Mercator (UTM)

The UTM maps the entire world by dividing it into 60 zones each 6° of longitude wide. When the UTM system is selected OpenWells software makes all datums available and allows for selection of any one of the 60 zones north or south.

US State Plane Coordinate System 1983

This system maps the United States. It is a combination of Transverse Mercator and Lambert Projections and comprises 124 zones. Most States have more than one zone - Alaska has 10 zones, California 6 but Maryland just one. Unlike the UTM projection, just one datum is used for the entire system - GRS 1980.

UK National Grid

This maps the United Kingdom, has one zone and is based on the National datum BGS.