EGM2008 - WGS 84 Version

EGM08 Geoid HeightsIntroduction

The official Earth Gravitational Model EGM2008 has been publicly released by the U.S. National Geospatial-Intelligence Agency (NGA) EGM Development Team. This gravitational model is complete to spherical harmonic degree and order 2159, and contains additional coefficients extending to degree 2190 and order 2159. Full access to the model's coefficients and other descriptive files with additional details about EGM2008 are provided herein.

Those wishing to use EGM2008 to compute geoid undulation values with respect to WGS 84, may do so using the self-contained suite of coefficient files, FORTRAN software, and pre-computed geoid grids provided on this web page. For other applications, the previous release of the full 'Geoscience' package for EGM2008 can be accessed through the link at the bottom of this web page.

The WGS 84 constants used to define the reference ellipsoid, and the associated normal gravity field, to which the geoid undulations are referenced are:

All synthesis software, coefficients, and pre-computed geoid grids listed below assume a Tide Free system, as far as permanent tide is concerned.

Note that the harmonic synthesis software provided below applies a constant, zero-degree term of -41 cm to all geoid undulations computed using EGM2008 with the height_anomaly-to-geoid_undulation correction model (also provided). Similarly, all pre-computed geoid undulations incorporate this constant zero-degree term. This term converts geoid undulations that are intrinsically referenced to an ideal mean-earth ellipsoid into undulations that are referenced to WGS 84. The value of -41 cm derives from a mean-earth ellipsoid for which the estimated parameters in the Tide Free system are: a=6378136.58 m and 1/f=298.257686.

Description of Software and Data

To compute point geoid undulations from spherical harmonic synthesis of the EGM2008 Tide Free Spherical Harmonic Coefficients and its associated Correction Model, at any WGS 84 latitude/longitude coordinate pair listed in a coordinate input file (such as INPUT.DAT), use the FORTRAN harmonic synthesis program, hsynth_WGS84.f.

At present, we are also providing two grids of pre-computed geoid undulations: one at 1 x 1-minute resolution and one at 2.5 x 2.5-minute resolution. To interpolate geoid undulations from the 1 x 1-Minute Geoid Undulation Grid file, for any WGS 84 latitude/longitude coordinate pair listed in a coordinate input file (such as INPUT.DAT), use the FORTRAN interpolation program interp_1min.f. Similarly, the FORTRAN interpolation program interp_2p5min.f, will interpolate geoid undulations from the 2.5 x 2.5-Minute Geoid Undulation Grid file.

Filenames containing a ".gz" in the suffix have been compressed using the Unix "gzip" command.

All files that are SMALL ENDIAN format are highlighted in green. All files that are BIG ENDIAN format are highlighted in purple.

Please carefully review the README_WGS84 file for a complete description of coefficient and data files for computing EGM2008 geoid undulations with respect to WGS 84. Also, before using any of the data files on this web page, please read the disclaimer.

New!For GIS data formats, please visit the EGM2008 GIS Data Page.

Software and Coefficients for WGS 84 Geoid Undulation Computations by Harmonic Synthesis

*Users - Please verify results by comparing to OUTPUT.DAT file immediately above.

Software and Grids for WGS 84 Geoid Undulation Computation by Interpolation

*Note: The 1 x 1 minute interpolation program below requires a large PC RAM capacity. *Users - Please verify results by comparing to OUTPUT.DAT file immediately above.

Software to Extract WGS 84 Geoid Undulations from Grid Files (No Interpolation)

Additional Information

Please provide comments, suggestions, and feedback to the contacts below as we strive to improve our EGM2008 products. Thank you!

Dr. Nikolaos Pavlis
NGA, Geodesy and Geophysics Basic and Applied Research
NGA Office of Geomatics (SN)
EGM2008 Development Team

Point of Contact: Office of Geomatics
phone (314) 676-9127, DSN 846-9127

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