NGA/NASA EGM96, N=M=360 Earth Gravitational Model

WGS 84 EGM96 15-Minute Geoid Height File and Coefficient File

The NGA/NASA Geoid Height File consists of a 15-minute grid of point values in the tide-free system, using the EGM96 Geopotential Model to degree and order 360. The WGS 84 constants used to define the geometry and the normal field of the reference ellipsoid in the calculation of this geoid height file are the following:

The geoid undulation values are calculated by applying a correction term that converts a pseudo-height anomaly calculated at a point on the ellipsoid to a geoid undulation value. In addition, a correction term of -0.53 m is added to the prior result to obtain the geoid undulation with respect to the WGS 84 ellipsoid. The value of -0.53 m is based on the following estimates of the equatorial radius (a) and flattening (f) of an ideal earth ellipsoid in the tide-free system: a=6378136.46 m and 1/f=298.25765. Details on the geoid undulation computations will be described in the joint project report on the EGM96 model.

The 15-minute geoid height grid is used as input to a FORTRAN program, INTPT.F, developed for interpolating from the grid, a geoid undulation at any given WGS 84 latitude and longitude. The program F477.F requires both the EGM96 spherical harmonic coefficient file and the correction coefficient file to calculate point geoid undulations at any given WGS 84 latitude and longitude by spherical harmonic synthesis. Refer to the User Instructions below for specific details on EGM96 files and programs.

Before using any of the software or data files on this web page, please click here and read the disclaimer.

DOS Users

For users who do not have access to a FORTRAN compiler, the executables for INTPT.F and F477.F have been compressed into one DOS self-extracting file. Before downloading this file, please check the instructions in the README file below and be aware the uncompressed versions of the two executables together will require a total of 7,344,408 bytes of space.

Online Geoid Calculator

Geoid Programs for Windows

Note: for the XP programs, an input.dat file is required with lines of geodetic latitude and longitude for all positions where you want the geoid height computed. There is a sample input.dat file included with each program.

Binary Files

For more information regarding the development of EGM96, please access the NASA/NGA EGM96 web site.

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

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