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:
- a=6378137.0 m (semi-major axis of WGS 84 Ellipsoid)
- f=1.0/298.2572235630 (flattening of WGS 84 Ellipsoid)
- GM=0.3986004418D15 m**3/s**2 (Earth's Gravitational Constant w/ atmosphere)
- OMEGA=7292115.D-11 radians/sec (Earth's angular velocity)
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.
- User Instructions (README File)
- FORTRAN Program INTPT.F
- Geoid Height File (3,326,955 bytes DOS self-extracting compressed; 9,756,647 bytes uncompressed)
- Geoid Height File (3,251,930 bytes UNIX compressed; 9,756,647 bytes uncompressed)
- FORTRAN Program F477.F
- EGM96 Coefficients (1,834,203 bytes DOS self-extracting compressed; 5,357,716 bytes uncompressed)
- EGM96 Coefficients (1,762,535 bytes UNIX compressed; 5,357,716 bytes uncompressed)
- Correction Coefficients (1,664,278 bytes DOS self-extracting compressed; 5,357,962 bytes uncompressed)
- Correction Coefficients (1,571,219 bytes UNIX compressed; 5,357,962 bytes uncompressed)
- Test Input Data
- Test Output Data for INTPT.F
- Test Output Data for F477.F
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
- INTPT geoid program for Windows XP (3.4 M, zip file, )
- F477 geoid program for Windows XP (3.6 M, zip file)
- EGM96 geoid program for Windows 95/NT (3.85 M, zip file)
- Binary Geoid Height File (unformatted direct access file, interpolation programs, readme file)
For more information regarding the development of EGM96, please access the NASA/NGA EGM96 web site.
phone (314) 676-9127, DSN 846-9127
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