Table of Contents

## What does GRS80 stand for?

The Geodetic Reference System 1980 (GRS 80) is a geodetic reference system consisting of a global reference ellipsoid and a normal gravity model.

**What is the difference between GRS80 and WGS84?**

Please note that the GRS80 and WGS84 are considered to be the same. Actually, there is a very small difference in the flattening which results in the semi-minor axis, b, being different by 0.0001 meters. There is no known application for which this difference is significant.

### What are the defining parameters of the Geodetic Reference System 1980?

The Geodetic Reference System 1980 GRS80 is still the conventional system for most applications in Geodesy and other Earth sciences. It was defined through the four parameters a (semi-major axis), J2 (Dynamical Form Factor), GM (geocentric Gravitational Constant) and ω (Angular Rotation Velocity).

**What does NAD 83 stand for?**

North American Datum of 1983

The North American Datum of 1983 (NAD 83) is the horizontal and geometric control datum for the United States, Canada, Mexico, and Central America. NAD 83 was released in 1986. State-by-state adjustments were completed in the 1990s, an effort referred to as the High Accuracy Reference Network (HARN).

#### What is GDA94 datum?

GDA94 is a coordinate reference system whose origin coincides with a determination of the centre of mass of the earth, hence the term ‘geocentric’. GDA94 is a ‘plate-fixed’ or ‘static’ coordinate datum based on the International Terrestrial Reference Frame 1992 (ITRF92), held at the reference epoch of 1 January 1994.

**Is GRS80 a datum?**

GRS80 is an ellipsoid (spheroid in Esri software), not an actual geodetic datum or coordinate reference system.

## What is ellipsoid in geodesy?

In geodesy, a reference ellipsoid is a mathematically-defined surface that approximates the geoid, the truer figure of the Earth, or other planetary body.

**What are NAD 83 and NAD27?**

NAD 27 and NAD 83 provide a frame of reference for latitude and longitude locations on Earth. Surveyors now rely almost exclusively on the Global Positioning System (GPS) to identify locations on the Earth and incorporate them into existing geodetic datums.

### What is the difference between MGA94 and GDA94?

GDA94 replaced the Australian Geodetic Datum 1966 (AGD66) and Australian Geodetic Datum 1984 (AGD84). The standard map projection associated with GDA94 is the Map Grid of Australia 1994 (MGA94), a transverse Mercator projection that conforms to the internationally accepted Universal Transverse Mercator Grid system.

**What is the difference between WGS84 and GDA94?**

GDA94 is a coordinate system specifically for Australia. WGS84 is developed for the DMA or United States Defense Mapping Agency which is now called the National Imagery and Mapping Agency or simply NIMA. It is the main geodetic reference system used by GPS systems.

#### What are datums used for?

A datum is a plane, a straight line, or a point that is used as a reference when processing a material or measuring the dimensions of a target.

**What is the difference between NAD27 and NAD 83?**

The NAD 27 was based on the Clarke Ellipsoid of 1866 and the NAD 83 is based on the Geodetic Reference System of 1980. The NAD 27 was computed with a single survey point, MEADES RANCH in Kansas, as the datum point, while the NAD 83 was computed as a geocentric reference system with no datum point.

## What datum is Google Maps in?

Google Maps and Microsoft Virtual Earth use a Mercator projection based on the World Geodetic System (WGS) 1984 geographic coordinate system (datum). This Mercator projection supports spheres only, unlike the ESRI Mercator implementation, which supports spheres and ellipsoids.