Earth Gravitational Model (EGM)
This division in the Office of Geomatics at NGA is responsible for collecting, processing, and evaluating gravity data (free-air and Bouguer gravity anomalies). These data are then used to compute gravimetric quantities such as mean gravity anomalies, geoid heights, deflections of the vertical, and gravity disturbances. All of these quantities are used in World Geodetic System 1984 support, navigation systems, mapping projects, and different types of surveys.
An Earth Gravitational Model (EGM) is set of geopotential coefficients used in a spherical harmonic expansion to create a global potential surface to coincide with Mean Sea Level (MSL). This surface is called a geoid and it fluctuates above and below the reference ellipsoid surface established by WGS 84. For more information, click on a drop-down menu item above on the EGM tab.
Earth Gravitational Model 2008 (EGM2008)
The EGM84 and EGM96 are legacy products. Users are recommend to use the latest EGM from NGA,currently EGM2008. In 2020, NGA plans to release a new EGM, tentatively named EGM2020, where uponEGM2008 will become a legacy product.
The EGM2008 is provided as a set of normalized, geopotential coefficients complete to degreeand order 2159, and contains additional spherical harmonic coefficients extending to degree 2190 andorder 2159. Also provided is a 2.5-minute worldwide geoid height file, precomputed from the EGM2008.The coefficient and geoid height files have associated software and documents. EGM2008 was approvedfor official DoD use as documented in NGA STND.0036_1.0, 2014-07-08.
| WHAT'S NEW |
|---|
April, 2013 - EGM2008 Citation included below with Links to reference EGM2008 and the EGM2008 Erratum are given on left under Additional Information. EGM2008 Citation: The development and evaluation of the Earth Gravitational Model 2008(EGM2008) - Nikolaos K. Pavlis, Simon A. Holmes, Steve C. Kenyon, John K. Factor; Journal ofGeophysical Research: Solid Earth (1978-2012) Volume 117, Issue B4, April 2012. |
| May, 2009 - Global 2.5 Minute Geoid Undulation Grid available in GIS format. |
| February, 2009 - Middle East Geoid Undulation Grid available in GIS format. |
| February, 2009 - Propagated Error Estimates of EGM2008 released. |
| January, 2009 - Utility to convert binary files from Big Endian to Small Endian released. |
| January, 2009 - Gravity Anomalies & Deflections of the Vertical data released. |
| November, 2008 - SMALL ENDIAN versions of binary files released. |
| November, 2008 - Files & Products for Oceanographic Applications released. |
| July, 2008 - WGS 84 version of EGM2008 released. Includes grids and programs for computing geoid undulations relative to WGS 84 Ellipsoid. |
Please contact the Office of Geomatics with comments, suggestions, and feedback.
Earth Gravitational Model 1996 (EGM96)
The EGM84 and EGM96 are legacy products. Users are recommend to use the latest EGM from NGA,currently EGM2008. In 2020, NGA plans to release a new EGM, tentatively named EGM2020, where uponEGM2008 will become a legacy product.
The EGM96 is provided as a set of normalized, geopotential coefficients to degree and order360. Also provided is a 15-minute worldwide geoid height file, precomputed from the EGM96. Thecoefficient and geoid height files have associated software and documents. EGM96 was approved forofficial DoD use as documented in NIMA TR8350.2, Third Edition, 4 July 1997.
Earth Gravitational Model 1984 (EGM84)
The EGM84 and EGM96 are legacy products. Users are recommend to use the latest EGM from NGA,currently EGM2008. In 2020, NGA plans to release a new EGM, tentatively named EGM2020, where uponEGM2008 will become a legacy product.
The EGM84 is provided as a set of normalized, geopotential coefficients to degree and order180. Also provided is a 30-minute worldwide geoid height file, precomputed from the EGM84. Thecoefficient and geoid height files have associated software and documents. EGM84 was approved forofficial DoD use as documented in DMA TR8350.2, Second Edition, 1 September 1991.
World Magnetic Model (WMM)
The World Magnetic Model is the standard model used by the U.S. Department of Defense, the U.K. Ministry of Defence, the North Atlantic TreatyOrganization (NATO) and the International Hydrographic Organization (IHO), for navigation, attitude and heading referencing systems using the geomagneticfield. It is also used widely in civilian navigation and heading systems. The model, associated software, and documentation (to be released early 2020)are distributed by NCEI on behalf of NGA. The model is produced at 5-year intervals, with the current model expiring on December 31, 2024.
Download WMM 2020
Datum Transformations & Conversions
Data acquired by NGA and referenced to a geodetic datum other than WGS 84 does not meet agency standards, and must therefore undergo a datumtransformation to WGS 84. For assistance setting up geographic translations, acquiring grid system and datum parameters, running batch conversions, andloading MSP Geotrans please refer to the GEOTRANS menu item on the Data/Apps tab.
Definitions
A transformation, or more specifically a geodetic datum transformation, is a change in a coordinate based onto what geodetic datum a coordinate is referenced. The NGA and DoD approved geographic translator to perform geodetic datum transformations is MSPGEOTRANS.
A conversion, or more specifically a coordinate conversion, is a change in coordinate data from one referencesystem to another. The NGA and DoD approved geographic translator to perform coordinate conversions is MSP GEOTRANS.
World Geodetic System 1984 Reference System
Brief Description: WGS 84 is an Earth-centered, Earth-fixed terrestrial reference system and geodetic datum. WGS 84 is based on a consistent set of constants and model parameters that describe the Earth's size, shape, and gravity and geomagnetic fields. WGS 84 is the standard U.S. Department of Defense definition of a global reference system for geospatial information and is the reference system for the Global Positioning System (GPS). It is compatible with the International Terrestrial Reference System (ITRS).
Definition:
• Origin Earth’s center of mass being defined for the whole Earth including oceans and atmosphere.
• Axes
- Z-Axis = The direction of the IERS Reference Pole (IRP). This direction corresponds to the direction of the BIH Conventional Terrestrial Pole (CTP) (epoch 1984.0) with an uncertainty of 0.005″.
- X-Axis = Intersection of the IERS Reference Meridian (IRM) and the plane passing through the origin and normal to the Z-axis. The IRM is coincident with the BIH Zero Meridian (epoch 1984.0) with an uncertainty of 0.005″.
- Y-Axis = Completes a right-handed, Earth-Centered Earth-Fixed (ECEF) orthogonal coordinate system.
• Scale Its scale is that of the local Earth frame, in the meaning of a relativistic theory of gravitation. Aligns with ITRS.
• Orientation Given by the Bureau International de l’Heure (BIH) orientation of 1984.0.
• Time Evolution Its time evolution in orientation will create no residual global rotation with regards to the crust.
Coordinate System: WGS 84 follows the criteria outlined in the International Earth Rotation Service (IERS) Technical Note 36. The WGS 84 Coordinate System origin also serves as the geometric center of the WGS 84 Ellipsoid and the Z-axis serves as the rotational axis of this ellipsoid of revolution. WGS 84 geodetic coordinates are generated using its reference ellipsoid.
Defining Parameters: WGS 84 identifies four defining parameters. These are the semi-major axis of the WGS 84 ellipsoid, the flattening factor of the Earth, the nominal mean angular velocity of the Earth, and the geocentric gravitational constant as specified below.
| Parameter | Notation | Value |
|---|---|---|
| Semi-major Axis | a | 6378137.0 meters |
| Flattening Factor of the Earth | 1/f | 298.257223563 |
| Nominal Mean Angular Velocity of the Earth | ω | 7292115 x 10-11 radians/second |
| Geocentric Gravitational Constant (Mass of Earth’s Atmosphere Included) | GM** | 3.986004418 x 1014 meter3/second2 |
**The value of GM for GPS users is 3.9860050x1014 m3/sec2 as specified in the reference below.
Relationship to International Terrestrial Reference Frame: The realization of a system into a frame is accomplished through the establishment of physical reference markers whose coordinates are consistent with its definition. Following this model, the WGS 84 Reference Frame (WGS 84 RF) is made real through the Cartesian coordinates of the Antenna Reference Points at the NGA/USSF GPS Monitor Stations. WGS 84 RF is aligned to ITRF to within one centimeter in each 3D component. At this level, NGA states the two frames are coincident for positioning, navigation, and targeting.
The 7-parameter transformation from WGS 84-to-ITRF is zero in all components by design. To support this claim two sets of metrics are provided:
- The 7-parameter transformations between the IGS GPS Precise Ephemerides and the NGA GPS Precise Ephemerides with the view that each is a reflection of their underlying reference frames.
- The offsets in Precise Point Positioning solutions using NGA GPS Precise Ephemerides to a subset of IGS stations’ coordinates as presented in the SINEX data.
Download IGS vs NGA
Download SINEX Offsets
Reference:
- National Geospatial-Intelligence Agency (NGA) Standardization Document “Department of Defense, World Geodetic System 1984, Its Definition and Relationships with Local Geodetic Systems” Version 1.0.0 NGA.STND.0036_1.0.0_WGS84 available in NSG Standards Registry
MSP (Mensuration Services Program) GEOTRANS (Geographic Translator) v3.9
MSP GEOTRANS is the NGA and DOD approved coordinate converter anddatum translator. The user-friendly GUI has features including batchconversion capability, a choice of precision levels, and the capabilityto add your own datum. MSP GEOTRANS can be downloaded to run as astand-alone application. Available downloads are listed (below).
Operating Systems and Compilers Supported:
- Windows 10, 32-bit, Visual Studio 2015
- Windows 10, 64-bit, Visual Studio 2015
- RHEL 7, 64-bit, GCC 4.8.5
NOTE: Since version 3.8, GeoTrans retired support for all Windows versions using theVisual Studio 2010, 2012, and 2013 compilers, and Red Hat Enterprise Linux 6.
New Enhancements:
- Added support for common European Petroleum Survey Group (EPSG) codes
Bug Fixes:
- Fixed a bug in the GARS::convertToGeodetic code to correct out-of-range longitudes
- Corrected a bug in an argument for the method DatumLibraryImplementation::GeodeticDatumShift
MSP GEOTRANS Documents
MSP GEOTRANS Downloads
GeoTrans 3.9 requires Java Runtime Environment (JRE) 1.8 or later to execute (JRE 1.8.0.256 or later is recommended). Refer to the MSP GeoTrans 3.9 Release Notesfor information on how to check your Java version and download JRE 1.8.0.256.
There are four versions of GeoTrans available for download, one intended for end users and three for software developers.After downloading the appropriate version please refer to the MSP GeoTrans 3.9 Release Notesfor proper installation instructions and for detailed descriptions of the changes included in this release.To verify download integrity, please get the checksums here.
End User Version:
The End User version is recommended for the majority of the GeoTrans users and contains everything necessary torun GeoTrans, to include the GeoTrans on-line help. Windows users should determine whether the 32- or 64-bitversion is appropriate for their installation based on whether they have a 32- or 64-bit version of Javainstalled.
- Windows 32-bit End User (Self-installer)
- Windows 64-bit End User (Self-installer)
- Windows End User (All Files)
- Linux End User (All Files)
Developer Version:
The Developer version is for software developers and contains the GeoTrans executable software plus the GeoTranssource code, documentation and a programmer's guide.
- Windows Developer
- Linux Developer
MGRS Version:
The MGRS version is for software developers who only need the MGRS, UTM, UPS, Transverse Mercator and PolarStereographic modules, source code and documentation. It does not include any GeoTrans executable software.
- MGRS Windows
- MGRS Linux
Master Version:
The Master version is for software developers and includes all of the GeoTrans executables for all platforms, allsource code and all documentation. The only difference between the Windows and Linux version is the method usedto zip the files.
- Windows Master
- Linux Master
MSP GEOTRANS Assistance
Having trouble starting GEOTRANS? Hereare some suggestions
If you have installed GEOTRANS and areunable to get it to start (no message given) you may need to downloadthe MS Visual C++ Redistributable Package. This software is normallyincluded on a computer, but system configurations do vary. Pleaseread the instructions for installing GEOTRANS on aNetwork Drive.
MS Visual C++ Redistributable Package for 32-bit user download: http://www.microsoft.com/en-us/download/details.aspx?id=5582
MS Visual C++ Redistributable Package for 64-bit user download: http://www.microsoft.com/en-us/download/details.aspx?id=14632
NOTE: Java 32-bit and 64-bit may be required to run MSP GEOTRANS.GEOTRANS 3.9 was built using Java JDK 1.8 update 256. The latestreleases of Java can be found at Oracle.com. Should you encounter a Windows Error2 condition during MSP GEOTRANS install, this error usually occursbecause the wrong bit-level for Java was selected. Especially withJava 1.8, the Windows environment variable for PATH is often not setcorrectly. You may try the following procedure to correct thecondition:
- Right click on Computer and select properties.
- On the left panel, click on Advanced system settings.
- At the bottom of the Advanced tab, click on EnvironmentVariables...
- Under the System variables, select Path and click Edit.
- Change the Variable values forC:\ProgramData\Oracle\Java\javapath to C:\Program Files(x86)\Java\<your java version>\bin
- Click Ok and exit out of the Advanced tab
Contact the MSP/GEOTRANS Help Desk
For assistance with MSP GEOTRANS software, including questions aboutsource code, please email MSP_Help@nga.mil(Unclassified content only).
Earth Gravitational Model 2008 (EGM2008) Data and Apps
The following links contain documentation, source code, data, and supporting inputs and tools for EGM2008.
Earth Gravitational Model 96 (EGM96) Data and Apps
The following links contain documentation, source code, data, and supporting inputs and tools for EGM96.
| FILE/LINK | DESCRIPTION |
|---|---|
| 360 Spherical Harmonics | Zip archive containing all EGM96 360 Spherical Harmonics code and documentation. |
| 15 Minute Interpolation Grid | Zip archive containing all EGM96 15 Minute Interpolation Grid code and documentation. |
| EGM96 and EGM08 Geoid Calculator | Online calculator to determine EGM96 and EGM08 geoid height based on latitude and longitudeinputs. |
Earth Gravitational Model 1984 (EGM84) Data and Apps
The following links contain documentation, source code, data, and supporting inputs and tools for EGM84.
| FILE/LINK | DESCRIPTION |
|---|---|
| 180 Spherical Harmonics | Zip archive containing all EGM84 Spherical Harmonics code and documentation. |
| 30 Minute Interpolation Grid | Zip archive containing all EGM84 30 Minute Interpolation Grid code and documentation. |
World Magnetic Model 2020 - Data
The World Magnetic Model (WMM) is a joint product of the United States' National Geospatial-Intelligence Agency(NGA)and the United Kingdom's DefenceGeographic Centre (DGC). The WMM was developed jointly by the National Centers for Environmental Information(NCEI, Boulder CO, USA) (formerly NationalGeophysical Data Center (NGDC)) and the British Geological Survey (BGS, Edinburgh, Scotland).Check the NOAA website on the open internet for the most recent annual report of the status of the WMM(https://www.ncei.noaa.gov/products/world-magnetic-model).
For more information on the WMM and how to implement the coefficients, please read theWMM 2020 Technical Report.
Download WMM 2020
World Magnetic Model 2020 - Apps
The NOAA/BGS calculators can be found on the open internet(https://www.ncei.noaa.gov/products/world-magnetic-model).
Reference Frame - Data
Relationship to International Terrestrial Reference Frame: The realization of a system into a frame is accomplished through the establishment of physical reference markers whose coordinates are consistent with its definition. Following this model, the WGS 84 Reference Frame (WGS 84 RF) is made real through the Cartesian coordinates of the Antenna Reference Points at the NGA/USSF GPS Monitor Stations. WGS 84 RF is aligned to ITRF to within one centimeter in each 3D component. At this level, NGA states the two frames are coincident for positioning, navigation, and targeting.
The 7-parameter transformation from WGS 84-to-ITRF is zero in all components by design. To support this claim two sets of metrics are provided:
- The 7-parameter transformations between the IGS GPS Precise Ephemerides and the NGA GPS Precise Ephemerides with the view that each is a reflection of their underlying reference frames.
- The offsets in Precise Point Positioning solutions using NGA GPS Precise Ephemerides to a subset of IGS stations’ coordinates as presented in the SINEX data.
Download IGS vs NGA
Download SINEX Offsets
Reference:
- National Geospatial-Intelligence Agency (NGA) Standardization Document “Department of Defense, World Geodetic System 1984, Its Definition and Relationships with Local Geodetic Systems” Version 1.0.0 NGA.STND.0036_1.0.0_WGS84 available in NSG Standards Registry
Services PKI certs required
Allows visualization via the IC Portal or ArcGIS desktop (download).After selecting the link below, additional viewing options may beavailable by following the link under the "Map Contents" heading.
| SERVICE NAME | LINK | DESCRIPTION |
|---|---|---|
| Earth Gravity Model 2008 (EGM08) | MoW REST Endpoint | EGM08 is an interpreted grid of the spherical harmonics model of the earth's gravitational potential. The grid was formed by merging terrestrial, alimetry-derived and airborne gravity data. EGM08 is complete to degree and order 2159, and contains additional coefficients up to degree 2190 and order 2159. |
| World Magnetic Model 2015 (WMM) | MoW REST Endpoint | The World Magnetic Model (WMM) is a set of data, software and charts used to characterize, depict, and predict various properties of the earth's magnetic field. Primarily used for portraying declination data (magnetic north) on maps and charts. The model is produced at 5-year intervals, with the current model expiring 31 Dec 2019. |
WGS 84 Resources & Links
| DOCUMENT | DESCRIPTION | DOCUMENT |
|---|---|---|
NGA.STND.0036_1.0.0_WGS84 | NGA Standardization Document, Department of Defense, World Geodetic System 1984 (updated 8 July 2014) | WGS 84 definition and relationships with local geodetic systems. |
