WGS84: What is the World Geodetic System 1984
The World Geodetic System (WGS) is a standard that defines Earth-centered, Earth-fixed (ECEF) models, Earth gravitational, and World Magnetic models. In 1983, a new realization of WGS—WGS84—was developed from modifications of the Navy Navigation Satellite System (NNSS). Today, that realization is used worldwide for global positioning and navigation in automotive and mobile devices.
This article will provide a detailed exploration of World Geodetic Systems (WGS) and explain their importance in specific fields such as construction surveying and mapping. It will also clarify some technical WGS terms and demonstrate how WGS determines location.
Finally, we’ll explore other related geographic coordinate systems and address frequently asked questions about WGS84 and other World Geodetic Systems.
What is WGS84?
WGS84 is a three-dimensional coordinate reference frame and the current world geodetic system standard used in navigation, mapping, drones, self-driving cars, robotics, satellite communications, and geospatial analysis. It comprises an ellipsoid, a horizontal datum, a vertical datum, and a coordinate system that accurately determines geographical locations.
For example, geodesists use WGS84 to define the coordinates of various locations on the Earth's surface so that they can say that a particular state or country is located at specific latitude and longitude coordinates.
Before becoming the accurate and reliable standard today, WGS 84 has undergone several updates. The first is WGS84 (G730), followed by WGS84(G873), then WGS84(1150), and the current WGS84(G1674), with each version becoming more accurate.
The WGS84 standard is the same one used with GPS devices, but people often confuse the WGS84 coordinate system with GPS, since GPS/GNSS can be used with any datum.
WGS84 vs GPS
GPS/GNSS can be used with any datum as they are fundamentally designed to be datum-agnostic. But how do the coordinates provided by global positioning systems differ from those of the world geodetic system?
Simply put, GPS coordinates can be converted to match different datums depending on the app's requirements or geographical area, but WGS84 remains consistent and is universally applied in GPS technologies. Also, while GPS typically provides raw satellite data that may initially reference a slightly different version of the WGS84 or other datums, WGS84 provides the standardized datum framework that aligns these coordinates globally.
For survey and geodetic tasks requiring high precision, like RTK surveying, a consistent, standardized coordinate reference system (CRS) such as WGS84 is absolutely necessary. Why? It supports absolute and relative navigation by providing a common reference framework for accurate positioning and data comparison across different geographic locations. This means construction surveyors and geospatial analysts can access precise measurements quickly. WGS84 is also used in other fields, such as robotics and self-driving cars.
What are coordinate reference systems? How do they work?
Coordinate reference systems use coordinates to define how two-dimensional projected maps relate to true locations on the Earth. For instance, CRS uses ellipsoids and geoids to model the Earth's size and shape so users can achieve precise navigation.
But do coordinate reference systems need standardization? Can you use any coordinate reference system on your GPS device? Let’s explain.
Ellipsoid or Geoid
Ellipsoids provide a mathematical representation of the Earth’s shape, while geoids show the Earth’s mean sea level (elevation information), which is used for measuring precise surface elevations.
Various coordinate reference frames and systems use ellipsoids to establish a base model of the Earth against which positional measurements are taken. These reference frames include WGS84, NAD83, ETRS89, GRS80, and many others. Each of these coordinate reference frames mentioned has its ellipsoid, with the world geodetic system of 1984 ellipsoid being the most popular one used as a reference surface for GPS coordinates.
On the other hand, geoids adjust the height calculations provided by ellipsoids to account for local variations in the Earth's gravity, which impacts sea levels and, thus, the actual height of locations. Together, ellipsoids and geoids create a detailed, accurate mapping and geographic data analysis system.
Geoids are also important in land surveying, topographic mapping, agricultural farm mapping, and navigation as they convert ellipsoidal heights to orthometric heights, which engineers, architects, and construction workers can use.
Horizontal Datum
A horizontal datum is a reference system that provides the longitude and latitude coordinates that determine exact locations on the Earth's surface. These datums measure movement in the earth's crusts, which can be further used to predict geological events and assess risk areas for engineering projects.
CRS uses horizontal datums to reference geodetic measurements to rectangular coordinates. This means converting complex spherical measurements into simpler, planar grids, and it is necessary for accurately mapping and modeling the Earth for various applications such as navigation and environmental management.
Vertical Datum
While horizontal datums deal with latitude and longitudes, vertical datums reveal elevation and depth data. Instead of measuring movements in the earth’s crust, these datums provide a reference point for height measurements necessary for constructing accurate topographical maps and models.
CRS uses vertical datums to accurately measure heights below or above a surface, which is usually the sea level, and ensure consistent and reliable elevation readings across different geographic regions and over time.
Units
Units in geodesy and coordinate reference systems are basically degrees, and these are how the data obtained from geographic measurements such as GPS readings are presented. Here’s an example: if a GPS device measures the longitude of a particular location, it might display that longitude as 34.0522 degrees West.
How WGS84 Determines Location
Here’s how GPS devices and mapping applications use WGS84 to determine geographic locations using an ellipsoid model, a horizontal, and a vertical datum.
WGS84 Unified Ellipsoid Model
GPS and mapping applications use the WGS84 Unified Ellipsoid Model as a reference surface to arrive at the correct coordinates for a particular location. How? GPS devices usually have receivers that detect signals from multiple satellites orbiting the Earth, including the Global Positioning System (GPS) from the United States, GLONASS from Russia, Galileo from the European Union, and BeiDou from China.
The signals from these major constellations interact with the ellipsoid model to compute accurate locations. GPS devices can translate satellite signals into precise ground coordinates by knowing the device’s position in reference to the WGS84 ellipsoid. GPS devices can also use RTK corrections to derive an even more accurate result up to 1 cm accuracy.
WGS84 Horizontal Datum
While the ellipsoid model is a reference surface and the basis for many geodetic datums, the horizontal datum establishes the measurement framework for precisely calculating longitude and latitude. With this, GPS devices can accurately determine precise geographic positions.
WGS84 Vertical Datum
The horizontal datum measures latitude and longitude, so if you want to assess elevation accurately, you’ll need a vertical datum. Vertical datums measure heights above or below a reference surface. However, most GPS devices have built-in support for horizontal and vertical data, so you won’t need to configure these settings manually.
Related Geographic Coordinate Systems
WGS84 is the most widely used geographic coordinate system, but there are also GRS 80, WGS72, NAD83, EPSG:3857, and EPSG:4326.
WGS72
WGS72 is the World Geodetic System of 1972, created by the U.S. Department of Defense. While it is no longer in use, it is one of the earlier versions of WGS before WGS84. It was a military standard datum used to produce three-second digital elevation models, which are now used to enhance historical data comparison and analysis.
GRS80
The Geodetic Reference System 1980 is the IAG's chosen standard for geodesy, earth science, and inertial navigation applications. It is the standard reference ellipsoid for the earth’s size and shape adopted by the International Union of Geodesy and Geophysics in 1979.
It is used the same way as the WGS84 but is a bit more flattened than the WGS84. Also, while WGS84 is used globally with global positioning systems, GRS80 accurately measures coordinates in the United States and Canada.
NAD83
NAD83 is the North American Datum 1983, a horizontal and geometric control datum for the United States, Canada, Mexico, and Central America. It uses survey monuments and triangulation techniques to create a reference frame for the Earth. It also uses the GRS80 ellipsoid to provide high accuracy in regional geospatial calculations, unlike WGS84, which uses a slightly different ellipsoid model for global consistency.
However, unlike WGS84, a global datum, NAD83 is a local datum because it is tied to the North American continent and originates from continental fixed points. While this may seem like a limitation, surveyors and geodesists who use NAD83 in the United States or any other country in North America will achieve more precise local measurements than if they use WGS84.
EPSG:3857
EPSG is an acronym for European Petroleum Survey Group. This group publishes data on coordinate systems on map projections and datums, and although it is not a recognized geodetic system, the EPSG:3857 is a spherical/web Mercator used for web mapping services such as Google Maps and OpenStreetMap.
EPSG:4326
The EPSG:4326 is the unique reference code used by WGS84. This reference code is a globally recognized identifier for geographic coordinate systems. The EPSG:4326 is actually sometimes referred to as the WGS84 projection because it is based on the world geodetic system ellipsoid of 1984
More About World Geodetic System 1984
There’s more to the world geodetic system of 1984, and here, we answer some of your most asked questions.
Is Google Maps in WGS84?
Google Maps uses a Mercator projection. However, this is still based on the World Geodetic System 1984 geographic coordinates. So, yes, Google Maps is in WGS84.
How do you plot WGS84 on a map?
To plot WGS84 coordinates on a map, you need the latitude and longitude values from WGS84. Next, use a GIS (Geographic Information System) software or an online mapping service like Google Maps to display the corresponding location on the map, using the WGS84 datum for accurate positioning.
What is a WGS84 coordinate example?
An example of a WGS84 coordinate would be the latitude and longitude for the Eiffel Tower in Paris, France: Latitude: 48.8584° N, Longitude: 2.2945° E. These coordinates mark the precise location using the WGS84 system, which you can enter into most GPS devices or mapping software to locate the Eiffel Tower.
Access Location Precision with Point One
Since its introduction in 1960 (WGS60), the World Geodetic Standard has been updated several times, from the WGS66, which introduced astrogeoids and astronautic mercury datum, to the current WGS84, which provides more sufficient data and has greater geographic coverage.
This article has explored WGS84 alongside other versions of the world geodetic systems and other related geographic coordinate frames. We have also shown the importance of accuracy in surveying and mapping and how more location and coordinate data equals a more accurate result than using traditional utility location techniques.
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