What is the World Geodetic System (WGS), and what are its primary applications?

The World Geodetic System (WGS) is a standard utilized in cartography, geodesy, and satellite navigation systems like GPS. It provides a consistent framework for representing the Earth's shape and gravitational field.

What is the current version of the World Geodetic System, and what key elements does it define?

The current version is WGS 84. It defines an Earth-centered, Earth-fixed coordinate system, a geodetic datum, and also describes the associated Earth Gravitational Model (EGM) and World Magnetic Model (WMM).

Which organization is responsible for the publication and maintenance of the World Geodetic System standard?

The World Geodetic System standard is published and maintained by the United States National Geospatial-Intelligence Agency (NGA).

What historical efforts in the 19th century contributed to the development of a unified geodetic system?

In the 19th century, F.R. Helmert's book 'Mathematical and Physical Theories of Physical Geodesy' laid theoretical groundwork. Additionally, organizations like the Central Bureau of International Geodesy in Austria and Germany were founded, leading to the derivation of several global ellipsoids for the Earth.

What were the primary driving forces behind the need for a unified geodetic system in the 1950s?

The need for a unified geodetic system arose due to the advent of international space science and astronautics, the lack of inter-continental geodetic information, the inadequacy of existing national geodetic systems for worldwide data, the requirement for global maps for navigation and geography, and Cold War preparedness necessitating a standardized NATO-wide geospatial reference system.

How did Cold War preparedness influence the development of standardized geospatial reference systems?

Western Cold War preparedness necessitated a standardized, NATO-wide geospatial reference system, which was established in accordance with the NATO Standardization Agreement.

When and by whom was the World Geodetic System 1960 (WGS 60) developed?

WGS 60 was developed in the late 1950s by combining the efforts of the U.S. Army, Navy, and Air Force, along with scientists from other institutions and countries, to create a unified world system for geodetic data.

What was a significant challenge in integrating data from various national geodetic systems into a global framework like WGS 60?

A substantial problem was re-referencing elevations. Traditional surveying methods referenced elevations to the local geoid, which is not easily determined by satellite geodesy, making it difficult to patch together data from different regions and reconcile elevation references for global mapping.

What types of data were utilized in the development of WGS 66?

The development of WGS 66 incorporated additional surface gravity observations, results from extended triangulation and trilateration networks, and significant amounts of Doppler and optical satellite data that had become available since WGS 60.

What were the defining parameters for the WGS 66 Ellipsoid?

The defining parameters for the WGS 66 Ellipsoid were its flattening, determined from satellite data to be 1/298.25, and its semi-major axis, measured at 6,378,145 meters, derived from a combination of Doppler satellite and astro-geodetic data.

How was the WGS 66 gravimetric geoid produced?

The WGS 66 gravimetric geoid was produced using a worldwide 5° x 5° mean free air gravity anomaly field, which served as the basic data.

What was the primary methodology used in the development of WGS 72?

WGS 72 was developed through a 'Unified WGS Solution,' which involved a large-scale least squares adjustment combining selected satellite, surface gravity, and astro-geodetic data available up to 1972 from both Department of Defense (DoD) and non-DoD sources.

What types of satellite data contributed to the development of WGS 72?

Both optical and electronic satellite data were used, including Doppler data from the U.S. Navy's Navigational Satellite System (NNSS) and GEOCEIVERS, SECOR (Sequential Collation of Range) data from the U.S. Army, and optical satellite data from the Worldwide Geometric Satellite Triangulation Program using BC-4 cameras. Data from the Smithsonian Astrophysical Observatory, including Baker-Nunn camera observations and some laser ranging, was also included.

What was the composition of the surface gravity field used in the Unified WGS Solution for WGS 72?

The surface gravity field consisted of 410 equal-area mean free air gravity anomalies (10° x 10°), with approximately 45% determined directly from observed gravity data and the rest from geophysically compatible approximations using gravity-geophysical correlation techniques.

How was astro-geodetic data incorporated into the Unified WGS Solution for WGS 72?

Astro-geodetic data, primarily in the form of deflection of the vertical components referenced to national geodetic datums, was used to create astro-geodetic geoid charts. These geoid heights provided additional, more detailed data for land areas within the Unified WGS Solution.

What were the adopted semimajor axis and flattening values for the WGS 72 Ellipsoid?

The WGS 72 Ellipsoid adopted a semimajor axis (a) of 6,378,135 meters and a flattening (f) of 1/298.26.

What factors led to the recognition of the need for a new world geodetic system in the early 1980s, replacing WGS 72?

WGS 72 was no longer sufficient due to limitations in data, geographic coverage, and product accuracy for current and anticipated applications. The availability of improved data, increased coverage, new data types, and enhanced techniques, such as satellite laser ranging, VLBI, and satellite radar altimetry, prompted the development of a new system.

What new data types and techniques became available for the development of WGS 84?

New data types included observations from Doppler, satellite laser ranging (SLR), very-long-baseline interferometry (VLBI), and satellite radar altimetry. An advanced least squares method called collocation also became available, allowing for consistent combination solutions from different measurement types related to the Earth's gravity field.

What is the WGS 84 reference system used for, and what is its approximate accuracy?

WGS 84 is the reference system used by the Global Positioning System (GPS). It is geocentric and globally consistent within approximately 1 meter.

How does the WGS 84 reference ellipsoid relate to the GRS 80 ellipsoid?

The WGS 84 reference ellipsoid is based on the GRS 80 ellipsoid but contains a very slight variation in its inverse flattening. This difference arose because WGS 84 was derived independently, and its resulting parameters were rounded to different significant digits, leading to a tiny difference in the semi-minor axis.

What are the primary ellipsoid parameters for GRS 80 and WGS 84, specifically the semi-major axis and inverse flattening?

For GRS 80, the semi-major axis (a) is 6,378,137.0 meters and the inverse flattening (1/f) is approximately 298.2572221008827. For WGS 84, the semi-major axis (a) is also 6,378,137.0 meters, but the inverse flattening (1/f) is 298.257223563.

Where is the coordinate origin of WGS 84 intended to be located, and what is the estimated uncertainty?

The coordinate origin of WGS 84 is intended to be located at the Earth's center of mass. The uncertainty in this location is believed to be less than 2 centimeters.

Which meridian serves as the zero longitude meridian for WGS 84, and how does it differ from the Greenwich meridian?

The zero longitude meridian for WGS 84 is the IERS Reference Meridian. This meridian is approximately 5.3 arc seconds, or about 102 meters, east of the Greenwich meridian at the latitude of the Royal Observatory in Greenwich.

At what approximate longitude do the longitude positions on WGS 84 agree with those on the North American Datum 1927?

The longitude positions on WGS 84 align with those on the older North American Datum 1927 at approximately 85° longitude west, in the east-central United States.

What are the key parameters defining the WGS 84 datum surface, including the equatorial radius, flattening, gravitational constant, and Earth's angular velocity?

The WGS 84 datum surface is an oblate spheroid with an equatorial radius (a) of 6,378,137.0 meters and a flattening (f) of 1/298.257223563. The refined gravitational constant (GM) is 3.986004418 x 10^14 m³/s², and the Earth's angular velocity (ω) is defined as 72.92115 x 10^-6 rad/s.

What is the calculated value for the polar semi-minor axis (b) and the first eccentricity squared (e²) for the WGS 84 ellipsoid?

For the WGS 84 ellipsoid, the polar semi-minor axis (b) is calculated as 6,356,752.3142 meters, and the first eccentricity squared (e²) is approximately 0.00669437999014.

What was the original standardization document for WGS 84, and who published it?

The original standardization document for WGS 84 was Technical Report 8350.2, published in September 1987 by the Defense Mapping Agency, which later became the National Imagery and Mapping Agency.

How has the accuracy of WGS 84 evolved with its updates, particularly concerning GPS observations?

The original WGS 84 model had an absolute accuracy of 1-2 meters. Subsequent updates, such as WGS84 (G730), incorporated GPS observations, reducing the accuracy to about 10 cm (root mean square) per component.

What is the latest reference frame update for WGS 84, and what other standards is it aligned with?

The most recent update is reference frame G2296, released on January 7, 2024. It is aligned with both the ITRF2020 (the most recent International Terrestrial Reference Frame realization) and the IGS20 (the frame used by the International GNSS Service).

How are updates to the geoid and the World Magnetic Model handled in relation to WGS 84?

Updates to the geoid for WGS 84 are now published separately as an Earth Gravitational Model (EGM), offering improved resolution and accuracy. Similarly, the World Magnetic Model (WMM) is updated independently. The current WGS 84 uses EGM2008 and WMM2020.

What are some of the EPSG codes associated with WGS 84 components, and what do they represent?

Key EPSG codes for WGS 84 include: EPSG:4326 for the 2D coordinate reference system, EPSG:4979 for the 3D coordinate reference system, EPSG:4978 for the geocentric 3D CRS, EPSG:7030 for the reference ellipsoid, and EPSG:6326 for the horizontal datum.

What related concepts or projects are listed under the 'See also' section that pertain to geodetic systems?

The 'See also' section lists related topics such as the Degree Confluence Project, Earth Gravitational Model, European Terrestrial Reference System 1989, Geo (microformat), geo URI scheme, Geographic Information System, Geotagging, GIS file formats, North American Datum, Point of Interest, Timeline of Earth estimates, and the TRANSIT system.

According to the text, what was the purpose of the 'Central Bureau of International Geodesy' founded in the 19th century?

The Central Bureau of International Geodesy was founded in the 19th century by Austria and Germany to advance the field of geodesy and contributed to the derivation of early global ellipsoids for the Earth.

What specific limitations of large geodetic systems like ED50 and NAD contributed to the need for a global system?

The limitations of large geodetic systems such as European Datum (ED50), North American Datum (NAD), and Tokyo Datum (TD) included their inability to provide a worldwide geo-data basis, which was increasingly necessary for global mapping, navigation, and aviation.

What was the role of the World Geodetic System Committee formed in 1966?

The World Geodetic System Committee, formed in January 1966 and composed of representatives from the U.S. Army, Navy, and Air Force, was tasked with developing an improved World Geodetic System (WGS 66) to meet evolving mapping, charting, and geodetic requirements.

What was the 'Unified WGS Solution' used in the development of WGS 72?

The 'Unified WGS Solution' was a large-scale least squares adjustment process that combined various types of available data, including satellite, surface gravity, and astro-geodetic measurements, to determine the most consistent set of geodetic positions and gravitational field parameters.

What was the purpose of including geodimeter long line precise traverses in the WGS 72 solution?

Geodimeter long line precise traverses were included in the WGS 72 solution to control the overall scale of the geodetic adjustment.

What is the approximate geocentric consistency of current geodetic realizations of the International Terrestrial Reference System (ITRS) compared to WGS 84?

Current geodetic realizations of the International Terrestrial Reference System (ITRS) are internally consistent at the few-centimeter level, while still being at the meter-level consistent with WGS 84. Both are geocentric.

What specific difference in the semi-minor axis exists between the GRS 80 and WGS 84 ellipsoids?

There is a tiny difference of approximately 0.105 mm in the semi-minor axis between the GRS 80 and WGS 84 ellipsoids, stemming from independent derivations and rounding of parameters.

What is the value of the WGS 84 reference ellipsoid's equatorial radius (a)?

The equatorial radius (a) of the WGS 84 reference ellipsoid is 6,378,137.0 meters.

What is the WGS 84 reference ellipsoid's flattening (f)?

The flattening (f) of the WGS 84 reference ellipsoid is 1/298.257223563.

What is the refined value for the WGS 84 gravitational constant (GM)?

The refined value for the WGS 84 gravitational constant (GM), including the Earth's atmosphere, is 3.986004418 x 10^14 m³/s².

What is the defined angular velocity (ω) of the Earth in WGS 84?

The defined angular velocity (ω) of the Earth in WGS 84 is 72.92115 x 10^-6 radians per second.

What was the Earth Gravitational Model (EGM) used in the original WGS 84 model?

The text mentions that the original WGS 84 model's Earth Gravitational Model (EGM) is documented in a 1991 DMA Technical Report, but it does not specify the exact EGM designation used in that initial version. However, it notes that current versions use EGM2008.

Which specific ITRF realization is the WGS 84 reference frame G2296 aligned with?

The WGS 84 reference frame G2296 is aligned with ITRF2020, which is the most recent realization of the International Terrestrial Reference Frame.

How is the orientation of a gravimetric datum depicted in relation to the geoid and an ellipsoid, according to the provided figure description?

The figure illustrates different orientations: an ellipsoid of an astro-geodetically oriented datum (shown with a cyan dotted line), the geoid (shown with a lime green line), and a gravimetrically-oriented ellipsoid (shown with a red dotted line).

What type of satellite ground stations were crucial for providing data for the development of WGS 72?

Doppler satellite ground stations, including those established by the U.S. Navy for the Navigational Satellite System (NNSS) and numerous sites equipped with GEOCEIVERS, were primary data sources for WGS 72 development.

What system utilized BC-4 cameras for worldwide geometric satellite triangulation as part of WGS 72 data collection?

The Worldwide Geometric Satellite Triangulation Program employed BC-4 cameras to gather optical satellite data, which was then used in the development of WGS 72.

How does the position of the Greenwich meridian relate to the WGS 84 datum's zero longitude meridian at the Royal Observatory?

The WGS 84 meridian of zero longitude, known as the IERS Reference Meridian, is located approximately 5.3 arc seconds (or 102 meters) east of the Greenwich meridian at the latitude of the Royal Observatory, Greenwich. This difference is due to local gravity field variations.

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What is the WGS?

Global Spatial Standard

The World Geodetic System (WGS) is a standard utilized in cartography, geodesy, and satellite navigation systems, most notably the Global Positioning System (GPS). It establishes a precise Earth-centered, Earth-fixed (ECEF) coordinate system and a geodetic datum, providing a consistent framework for defining locations worldwide.^[1]

Defining Our Planet

The current iteration, WGS 84, defines not only the coordinate system and datum but also an associated Earth Gravitational Model (EGM) and World Magnetic Model (WMM). This comprehensive system is maintained by the United States National Geospatial-Intelligence Agency (NGA), ensuring global standardization for geospatial data.^[1]

Precision and Consistency

WGS provides the foundational reference for all geospatial activities, from precise scientific measurements to everyday navigation. Its evolution reflects advancements in measurement technologies and a growing need for globally consistent, high-accuracy spatial data.^[1]

Historical Evolution

Early Foundations

The need for a unified global geodetic system emerged in the mid-20th century, driven by advancements in space science, astronautics, and the limitations of existing national geodetic systems. Early efforts, building on 19th-century work by figures like F.R. Helmert, aimed to create compatible worldwide geo-data bases for navigation, aviation, and geography.^[2]

WGS 60 & 66

The Department of Defense World Geodetic System 1960 (WGS 60) was an early attempt to consolidate various national systems. It faced challenges in reconciling data collected using different methods, particularly regarding elevation references. WGS 66 represented an improvement, incorporating more satellite data and refining ellipsoid parameters.^[3]

WGS 72: A Unified Solution

Developed over three years, WGS 72 was a significant step, utilizing an extensive collection of optical and electronic satellite data (Doppler, SECOR, BC-4 cameras) alongside surface gravity and astrogeodetic measurements. This "Unified WGS Solution" provided improved geodetic positions and gravitational field parameters.^[3]

WGS 84: The Modern Standard

Recognizing the limitations of WGS 72, WGS 84 was developed in the early 1980s. It incorporated new data types like satellite radar altimetry and advanced techniques like collocation. As the reference system for GPS, WGS 84 provides a geocentric, globally consistent framework with high accuracy, forming the bedrock of modern positioning.^[1]^[4]

WGS 84 Definition

Geocentric Framework

The WGS 84 coordinate origin is precisely at the Earth's center of mass, with an uncertainty estimated to be less than 2 centimeters. Its primary meridian is the IERS Reference Meridian, which is slightly east of the Greenwich meridian due to local gravitational variations.^[7]^[9]

Ellipsoid Parameters

WGS 84 defines a reference ellipsoid, closely based on the GRS 80 system, which approximates the Earth's shape. The key parameters are:

Ellipsoid Reference	Semi-major axis $a$	Semi-minor axis $b$	Inverse Flattening 1⁄ $f$
GRS 80	6,378,137.0 m	≈ 6,356,752.314140 m	298.257222100882711...
WGS 84^[6]	6,378,137.0 m	≈ 6,356,752.314245 m	298.257223563

These parameters define the precise dimensions of the reference spheroid used for calculations.^[5]^[6]

Derived Constants

Further constants derived from these parameters include the polar semi-minor axis ( $b$ ), the first eccentricity squared ( $e 2$ ), the standard gravitational parameter ( $GM$ ), and the Earth's angular velocity ( $ω$ ). These are crucial for accurate orbital mechanics and geodetic computations.^[11]

Updates and Evolution

Iterative Refinements

WGS 84 has undergone several updates since its initial publication in 1987 to incorporate new data and improve accuracy. These revisions, such as G730, G873, G1150, G1762, and most recently G2296 (released January 2024), align the system with the latest International Terrestrial Reference Frame (ITRF) realizations and International GNSS Service (IGS) standards.^[14]^[16]

Enhanced Accuracy

Initial WGS 84 models had an absolute accuracy of 1-2 meters. Subsequent updates, leveraging GPS observations, have progressively reduced this error. For instance, WGS84 (G730) achieved accuracies down to 10 cm per component (rms), reflecting the continuous advancement in measurement precision.^[14]

Separate Models

While the core WGS 84 reference frame is updated periodically, its associated Earth Gravitational Model (EGM) and World Magnetic Model (WMM) are now published and updated separately. The current WGS 84 implementation utilizes EGM2008 and WMM2020, providing enhanced resolution and accuracy for these critical components.^[18]^[19]

System Identifiers

EPSG Codes

The WGS 84 system and its components are formally identified using codes within the EPSG Geodetic Parameter Dataset. These standardized identifiers ensure unambiguous reference across different geospatial software and databases.

EPSG:4326 – 2D coordinate reference system (CRS)
EPSG:4979 – 3D CRS
EPSG:4978 – Geocentric 3D CRS
EPSG:7030 – Reference ellipsoid
EPSG:6326 – Horizontal datum

These codes are essential for interoperability in GIS and surveying applications.^[21]

Related Concepts

Fundamental Geodesy

WGS is built upon core principles of geodesy. Understanding concepts like the geoid, reference ellipsoids, map projections, and coordinate systems is fundamental to appreciating its role.

Geoid
Reference Ellipsoid
Geodetic Datum
Map Projection
Latitude & Longitude
Spatial Reference System

Navigation Technologies

WGS 84 is intrinsically linked to satellite navigation. Technologies that rely on it include global navigation satellite systems (GNSS) and related positioning techniques.

Global Positioning System (GPS)
Satellite Navigation Systems
Geotagging
Geographic Information Systems (GIS)

Historical Context

The development of WGS is part of a broader history of measurement, mapping, and understanding our planet's shape and gravity field.

History of Geodesy
Geodetic Datum Evolution
Timeline of Earth Estimates

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References

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This page was generated by an Artificial Intelligence and is intended for informational and educational purposes only. The content is based on a snapshot of publicly available data from Wikipedia and may not be entirely accurate, complete, or up-to-date.

This is not professional geodetic or mapping advice. The information provided on this website is not a substitute for professional consultation, diagnosis, or treatment. Always refer to official documentation and consult with qualified geospatial professionals for specific project needs. Never disregard professional advice because of something you have read on this website.

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The World Geodetic System

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What is the WGS? ℹ️

🌍 Global Spatial Standard

🛰️ Defining Our Planet

📐 Precision and Consistency

Historical Evolution 📜

⏳ Early Foundations

🚀 WGS 60 & 66

📡 WGS 72: A Unified Solution

📍 WGS 84: The Modern Standard

WGS 84 Definition ⚙️

🌐 Geocentric Framework

📊 Ellipsoid Parameters

🧮 Derived Constants

Updates and Evolution 🔄

📈 Iterative Refinements

🛰️ Enhanced Accuracy

🗺️ Separate Models

System Identifiers 🆔

🔢 EPSG Codes

Related Concepts 🔗

🧭 Fundamental Geodesy

🛰️ Navigation Technologies

📜 Historical Context

Teacher's Corner 🧑‍🏫

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Disclaimer ⚠️

📜 Important Notice

Dive in with Flashcard Learning!

What is the WGS?

Global Spatial Standard

Defining Our Planet

Precision and Consistency

Historical Evolution

Early Foundations

WGS 60 & 66

WGS 72: A Unified Solution

WGS 84: The Modern Standard

WGS 84 Definition

Geocentric Framework

Ellipsoid Parameters

Derived Constants

Updates and Evolution

Iterative Refinements

Enhanced Accuracy

Separate Models

System Identifiers

EPSG Codes

Related Concepts

Fundamental Geodesy

Navigation Technologies

Historical Context

Teacher's Corner

True or False?

Test Your Knowledge!

Gamer's Corner

Discover other topics to study!

References

Feedback & Support

Disclaimer

Important Notice