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gnssconstellation

Satellite locations at specified time

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Syntax

[satPos,satVel] = gnssconstellation(t)

Description

example

[satPos,satVel] = gnssconstellation(t) returns the satellite positions and velocities at the datetime t. The function returns positions and velocities in the Earth-centered Earth-fixed (ECEF) coordinate system in meters and meters per second, respectively.

Examples

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Open Live Script

Get the current satellite positions and velocities from the GNSS satellites. Access the orbital parameters from IS-GPS-200K Interface Specification and calculate the position and velocities in ECEF coordinates for the given time. Display the satellite positions.

t = datetime('now','TimeZone','Local');
[satPos,satVel] = gnssconstellation(t);
disp(satPos)
   1.0e+07 *

   -1.5213    0.0809    2.1756
    0.5704    2.5220   -0.6071
    0.2122   -2.5969   -0.5148
    0.9433   -1.9737   -1.5063
    0.5621    1.4400   -2.1598
    1.5956    0.6465   -2.0224
   -2.1452    1.5560   -0.1765
    0.8640   -1.9216    1.6171
   -2.3605    0.7396    0.9669
   -1.5869    0.7606   -1.9893
    2.1404    1.4844   -0.5192
    2.4674    0.7058    0.6840
   -0.4427   -1.7501    1.9482
   -1.1443   -1.8875   -1.4772
    1.5098    0.5879    2.1046
    1.4713   -0.5469    2.1425
   -0.7977    2.1657   -1.3144
   -0.4301   -2.5900   -0.4014
    2.3716   -0.9618    0.7104
   -0.5730    1.8760    1.7907
   -1.6045   -0.6373   -2.0183
   -1.6795    1.8525    0.8954
    0.5554    1.7697    1.9010
   -2.3407   -1.2516   -0.0937
   -2.4460   -0.5383    0.8840
    1.3565   -0.9463   -2.0782
    2.2091   -0.0434   -1.4738
Open Live Script

Use the lookangles function to get the azimuth and elevation angles of satellites for given satellite and receiver positions. Specify a mask angle of 5 degrees. Get the satellite positions using the gnssconstellation function.

Specify a receiver position in geodetic coordinates (latitude, longitude, altitude). 

recPos = [42 -71 50];

Get the satellite positions for the current time.

t = datetime('now');
gpsSatPos = gnssconstellation(t);

Specify a mask angle of 5 degrees. 

maskAngle = 5;

Get the azimuth and elevation look angles for the satellite positions. The vis output indicates which satellites are visible. Get the total using nnz.

[az,el,vis] = lookangles(recPos,gpsSatPos,maskAngle);
fprintf('%d satellites visible at %s.\n',nnz(vis),t);
9 satellites visible at 01-Sep-2021 14:09:24.

Input Arguments

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Current time for the satellite simulation, specified as a scalar datetime array.

The default time zone for a datetime array is UTC. For information on specifying a different time zone, see datetime.

GPS start time is Jan 6, 1980 midnight, UTC. Specifying any datetime prior to this time will use the GPS start time.

Example: datetime('now','TimeZone','Local');

Data Types: datetime

Output Arguments

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Satellite positions in the Earth-centered Earth-fixed (ECEF) coordinate system in meters, returned as an N-by-3 matrix of scalars. N is the number of satellites in the constellation.

Data Types: single | double

Satellite velocities in the Earth-centered Earth-fixed (ECEF) coordinate system in meters per second, returned as an N-by-3 matrix of scalars. N is the number of satellites in the constellation.

Data Types: single | double

More About

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Orbital Parameters

The initial satellite positions and velocities are defined by orbital parameters in Table A.2-2 in GPS SPS Performance Standard, and are given in Earth-centered Earth-fixed (ECEF) coordinates.

Position calculations use equations from Table 30-II in the same IS-GPS-200K Interface Specification.

Velocity calculations use equations 8.21–8.27 in [1].

References

[1] Groves, Paul D. Principles of GNSS, Inertial, and Multisensor Integrated Navigation Systems. Boston: Artech House, 2013.

Extended Capabilities

See Also

Objects

Functions

Topics

Introduced in R2021a

Navigation Toolbox Documentation

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