Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
1999-05-11
2001-06-19
Gregory, Bernarr E. (Department: 3662)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C701S200000, C701S207000, C701S221000
Reexamination Certificate
active
06249745
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
(Not applicable)
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
(Not applicable)
BACKGROUND OF THE INVENTION
This invention relates generally to inertial navigation systems which require gravity vector data in their operational regions and more specifically to methods for determining the deflection of the gravity vector at a point above the earth's surface given gravity vector deflection data for a three-dimensional grid of points above the earth's surface.
World wide deflection of vertical (DOV) data provided by the National Imagery and Mapping Agency (NIMA) can be used to compensate the mismodeled gravity vector error, thereby reducing velocity and position errors from an inertial navigation system.
NIMA provides DOV data on 32 CD-ROMs with each CD/ROM containing a 45°×45° sector of data. DOV data (East-West, North-South, as well as associated accuracies) are stored in files corresponding to grid points that are 2 arcminutes apart in 1°×1° cells.
The future NIMA DOV database will consist of 180×360+1=64,801 files at one altitude. There will be seven reference altitudes at 0, 10K, 20K, 30K, 50K, 70K, and 90K feet. This represents the NIMA-supplied data for the F-117 aircraft.
Each of the 64,801 files (except for the one discussed in the next paragraph) contains DOV data and accuracy data (all in arcseconds) of 900 grid points at 2 arcminutes spacing in a 1°×1° angular cell as shown in FIG.
1
. The files are labeled from N
01000
, N
01001
, . . . , N
01359
, N
02000
, . . . , to N
90359
and S
0000
, S
00001
, . . . , S
00359
, S
01000
, . . . , to S
89359
. Each file is 29,025 bytes in size.
The remaining file is named S
90000
. It contains the DOV and accuracy data for the south pole repeated 900 times to maintain the uniformity of data files.
BRIEF SUMMARY OF THE INVENTION
The invention is a method and apparatus for gravity vector compensation in an inertial navigation system (INS). The INS obtains its position, in terms of latitude, longitude and altitude, and determines a gravity-model vector at its position using a predetermined gravity model. There is an error between the gravity-model vector and the true gravity vector.
The error in the direction of the gravity-model vector is referred to as deflection of vertical (DOV), the DOV being expressed in terms of a North-South (N-S) DOV component and an East-West (E-W) DOV component. Matrices of N-S DOV and E-W DOV data are stored in memory in a plurality of files for a plurality of discrete points distributed over the surface of the earth at a plurality of altitudes.
The elements of a matrix of N-S DOV data or E-W DOV data have a one-to-one correspondence with a two-dimensional array of discrete contiguous points at a specified altitude above the earth's surface, the array of points having (1) latitude values in a specified range of latitude values, (2) longitude values in a specified range of longitude values, and (3) an altitude value in a specified range of altitude values. Adjacent elements in a matrix correspond to (1) adjacent points on a parallel of latitude or (2) adjacent points on a half-circle meridian, a half-circle meridian terminating at the two poles of the earth.
The first step of the method consists of obtaining the INS position.
The second step of the method consists of separately translating the N-S DOV data and the E-W DOV data from a plurality of matrices into a plurality of supermatrices. The INS latitude and longitude values are within the specified ranges of latitude and longitude and the INS altitude is greater than the altitude value of at least one matrix. The INS latitude and longitude values are within the specified ranges of latitude and longitude, and the INS altitude is less than the altitude value of at least one matrix.
The adjacent elements of a supermatrix correspond to (1) adjacent points on a parallel of latitude or (2) adjacent points on a whole-circle meridian. The elements of a supermatrix all correspond to the same altitude value.
The third step of the method consists of determining the N-S DOV and the E-W DOV at the INS position utilizing data from the plurality of supermatrices.
The fourth step of the method consists of compensating the direction of the gravity-model vector for the N-S DOV and the E-W DOV.
REFERENCES:
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patent: 5272639 (1993-12-01), McGuffin
patent: 5305236 (1994-04-01), Germanetti
patent: 5321631 (1994-06-01), Germanetti
patent: 5339684 (1994-08-01), Jircitano et al.
patent: 5402340 (1995-03-01), White et al.
patent: 5774832 (1998-06-01), Vanderwerf
patent: 6073077 (2000-06-01), Hsu
Brockstein Allan J.
Hsu David Y.
Gregory Bernarr E.
Litton Systems Inc.
Malm Robert E.
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