WGS84 – World Geodetic System 1984: Aviation and Surveying Glossary

Introduction

WGS84 (World Geodetic System 1984) is the foundational global geodetic reference system used for positioning, navigation, mapping, and geospatial data exchange. Established in 1984 and managed by the United States Department of Defense and the National Geospatial-Intelligence Agency (NGA), WGS84 forms the backbone of the Global Positioning System (GPS) and is universally adopted for all major global navigation satellite systems (GNSS), cartographic products, and aviation standards.

WGS84 defines the shape and size of the Earth, its orientation in space, and the associated gravity and magnetic models. Its rigorous, Earth-centered, Earth-fixed (ECEF) framework ensures that latitude and longitude anywhere on the globe are referenced to the same mathematical surface and origin. This uniformity eliminates the ambiguities and distortions that arose from older regional datums, providing seamless integration and compatibility for all geospatial applications.

WGS84 Reference Ellipsoid

The WGS84 reference ellipsoid is a mathematically defined, oblate spheroid that closely approximates the shape of the Earth, accounting for its equatorial bulge and polar flattening. It is defined by two key parameters:

• Semi-major axis (a): 6,378,137.0 meters (the equatorial radius)
• Flattening (f): 1/298.257223563

These parameters are derived from global geodetic data and satellite measurements, making the WGS84 ellipsoid both globally representative and highly precise. The semi-minor axis (b), or polar radius, is calculated as b = a × (1 – f) = 6,356,752.314245 meters.

The WGS84 ellipsoid is an Earth-centered model, with its origin at the Earth’s center of mass. This central positioning is essential for satellite-based navigation and global geospatial referencing.

Comparison with Other Ellipsoids

While WGS84 is nearly identical to ellipsoids like GRS80 (used in NAD83), even slight differences in flattening or axis length can cause measurable discrepancies in high-precision applications. Thus, accurate datum management and transformation are critical when integrating data from different sources.

Horizontal Datum

The horizontal datum of WGS84 defines how the reference ellipsoid is anchored to the real Earth. WGS84’s horizontal datum is Earth-centered and geocentric, with its origin at the planet’s mass center, including oceans and atmosphere.

WGS84 Coordinate Axes

• Z-axis: Aligned with the Earth’s mean rotational axis (IERS Reference Pole)
• X-axis: Intersects the equator at the IERS Reference Meridian (close to Greenwich)
• Y-axis: Completes a right-handed system, lying in the equatorial plane 90° east of the X-axis

This geocentric framework enables seamless integration of GNSS, remote sensing, and mapping data worldwide.

Aviation and Global Standards

The International Civil Aviation Organization (ICAO) mandates WGS84 for all aeronautical charts, navigation databases, and geospatial products, ensuring safety and interoperability in international air navigation. Surveyors and GIS professionals must be vigilant in transforming legacy or regional datum data to WGS84 for consistency.

Vertical Datum

WGS84 primarily defines heights as ellipsoidal heights (h)—the perpendicular distance from a point to the WGS84 ellipsoid. However, most practical applications require orthometric heights (H), which are referenced to the geoid (approximate mean sea level).

The relationship is:
H = h – N
where N is the geoid undulation, derived from Earth gravity models such as EGM2008.

Use in Practice

• GNSS receivers provide ellipsoidal heights by default.
• Engineering and aviation require conversion to orthometric heights using the latest geoid models.
• Accuracy of vertical data depends on the precision of the geoid model.

WGS84 Coordinate Systems

WGS84 supports several coordinate systems to suit different applications:

Geodetic Coordinates

• Latitude (φ), Longitude (λ), Ellipsoidal Height (h)
• Standard for navigation, mapping, and aviation

ECEF (Earth-Centered, Earth-Fixed)

• X, Y, Z Cartesian coordinates centered at the Earth’s mass center
• Essential for satellite operations and high-precision geodesy

Geographic Coordinate System (GCS)

• WGS84 GCS uses angular units (degrees) for latitude/longitude and the Greenwich meridian
• Most common GCS code: EPSG:4326

Projected Coordinate Systems

• UTM (Universal Transverse Mercator) and others transform geodetic coordinates to planar X, Y coordinates for local accuracy
• Used in engineering, large-scale mapping, and navigation

WGS84 Technical Parameters and Constants

These constants are internationally standardized and underpin all geodetic calculations, satellite orbits, and GNSS operations.

WGS84 Realizations and Reference Frames

WGS84 is periodically updated through new realizations, each reflecting improved satellite measurements and alignment with the International Terrestrial Reference Frame (ITRF).

Each realization updates GNSS reference station positions to maintain centimeter-level accuracy despite crustal motion and technological advances.

Earth Gravitational and Magnetic Models

Earth Gravitational Model (EGM)

WGS84 incorporates the Earth Gravitational Model (EGM)—currently EGM2008—to define the global geoid for orthometric height conversion. EGM2008 provides geoid undulation data globally at 9 km resolution, enabling precise conversion between ellipsoidal and orthometric heights.

World Magnetic Model (WMM)

The World Magnetic Model (WMM) describes the Earth’s main magnetic field and is updated every five years. WMM is essential for navigation systems, compass correction, and heading calculation. Both EGM and WMM are maintained by the NGA and are critical for aviation, navigation, and surveying.

Coordinate Transformations and Conversions

Datum Transformation

When converting coordinates between different datums (e.g., NAD83, ETRS89 to WGS84), a 7-parameter Helmert transformation is commonly used. This applies translations, rotations, and scale factors to ensure high-accuracy spatial alignment. The NGA’s GEOTRANS tool is the standard for such transformations.

Coordinate System Conversion

Conversions between geodetic, ECEF, and projected systems (like UTM) are routine in surveying, mapping, and navigation. Accurate conversions ensure consistent positioning across platforms and applications.

Applications in Surveying, Mapping, and Aviation

Surveying

WGS84 is the default reference for all GNSS-based surveying, supporting real-time kinematic (RTK), post-processed surveys, and establishment of geodetic control networks. Accurate transformations and geoid corrections are essential for integrating GNSS data into engineering and cadastral workflows.

Mapping and GIS

All modern GIS software, web maps, and spatial databases use WGS84 (EPSG:4326) as their base reference. This enables seamless integration of spatial data from diverse sources and supports high-precision mapping and analysis.

Aviation

WGS84 is mandated by ICAO for all aviation navigation, charting, and obstacle databases, supporting global safety and interoperability. All aircraft GNSS navigation is referenced to WGS84, and airport/runway elevations are now reported in WGS84-derived orthometric heights.

Conclusion

WGS84 is the global geodetic reference system enabling consistent, accurate positioning and navigation worldwide. It underpins GPS, aviation, surveying, mapping, and countless geospatial technologies, making it essential for modern infrastructure, commerce, and research. With continuous improvements and broad international adoption, WGS84 guarantees the precision and interoperability required in a connected, data-driven world.