gnssconstellation

Satellite locations at specified time

Since R2021a

Syntax

[satPos,satVel] = gnssconstellation(t)

[satPos,satVel,satID] = gnssconstellation(t,navData)

[satPos,satVel,satID] = gnssconstellation(t,navData,GNSSFileType=gnssFileType)

Description

[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. If the time zone for the datetime is not specified, it is assumed to be UTC.

[satPos,satVel,satID] = gnssconstellation(t,navData) returns the satellite positions, velocities, and IDs at time t in the specified RINEX navigation message data navData.

[satPos,satVel,satID] = gnssconstellation(t,navData,GNSSFileType=gnssFileType) additionally specifies the GNSS file type from which you obtained the navigation message data. This syntax enables you to process navigation data obtained from either a RINEX file, a SEM almanac file, a YUMA almanac file, or a Galileo XML almanac file.

Note

The gnssconstellation function determines the satellite position and satellite velocities by propagating the current orbital parameters specified by the RINEX file, SEM almanac file, a YUMA almanac file, or a Galileo XML almanac file to the query time. To get more accurate satellite positions and velocities, ensure you are using the navigation file released for the time that you are querying at. For more information about orbital parameter validity, see Orbital Parameters.

Examples

Get Current Satellite Positions and Velocities

Get the current satellite positions and velocities from the GNSS satellites. Access the orbital parameters from IS-GPS-200M 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 *

   -1.9738   -1.6924    0.5423
   -0.0966    1.8843    1.8693
    1.1229   -1.0301   -2.1754
    1.8545    0.1075   -1.8983
   -0.6657    2.5548   -0.2893
    0.1527    2.3194   -1.2850
   -1.6448    0.3583    2.0543
    1.4311   -2.0006   -1.0018
   -1.2327   -0.9999    2.1295
   -2.6199    0.2577    0.3522
    0.3252    1.4886   -2.1755
    1.6598    0.9807   -1.8269
    1.7770   -1.3634    1.4274
   -0.8460   -2.2270    1.1743
    1.7399    2.0067   -0.0045
    2.0627    1.4073    0.9051
   -1.7310    0.1523   -2.0086
    0.2985   -1.7578    1.9685
    1.3683    0.6911    2.1690
   -1.3061    2.1892   -0.7454
   -0.1612   -2.3139   -1.2939
   -1.6642    1.1897   -1.6938
   -1.6852    1.3990    1.5024
   -0.8307   -1.3560   -2.1273
   -1.8518   -0.8541   -1.7017
    2.6179   -0.4369    0.1005
    2.3492    0.3840    1.1782

Get Satellite Look Angles for Receiver Position

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 07-Mar-2024 15:43:35.

Retrieve Satellite Positions, Velocities, and IDs from RINEX File

Read one set of GPS satellites from the GPS navigation message in a RINEX file.

filename = "GODS00USA_R_20211750000_01D_GN.rnx"; 
data = rinexread(filename);
gpsData = data.GPS;
[~,satIdx] = unique(gpsData.SatelliteID);
gpsData = gpsData(satIdx,:);

Get the satellite positions, velocities, and IDs at the first time step.

t = gpsData.Time(1);
[satPos,satVel,satID] = gnssconstellation(t,gpsData)

satPos = 31×3
107 ×

   -1.5630   -0.1882    2.1186
    1.3808    2.1970   -0.4861
   -2.0061    0.7606    1.5492
   -2.5625   -0.0140   -0.7096
    1.4896    0.5448   -2.1487
    0.6129    2.5407    0.4615
   -1.0081    1.3751   -1.9877
   -2.5811   -0.6135   -0.3246
   -1.9289    0.8690   -1.6134
    0.9542   -2.2526    1.0113
      ⋮

satVel = 31×3
103 ×

   -0.8888   -2.5914   -0.8416
    0.0362    0.7543    3.1043
    1.1203   -1.6505    2.2591
   -0.8301   -0.4385    2.9967
   -1.6023    2.1607   -0.5493
   -0.3948   -0.4708    3.1591
   -1.0322   -2.4133   -1.1748
    0.4370   -0.1710   -3.1339
   -1.9860   -0.5032    2.1087
    0.9968   -0.8308   -2.8502
      ⋮

satID = 31×1

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      ⋮

Retrieve Satellite Positions, Velocities, and IDs from SEM Almanac File

Read GPS navigation message data from a SEM almanac file.

data = semread("semalmanac_2022-4-10.al3")

data=31×16 timetable
            Time            GPSWeekNumber    GPSTimeOfApplicability    PRNNumber    SVN    AverageURANumber    Eccentricity    InclinationOffset    RateOfRightAscension    SqrtOfSemiMajorAxis    GeographicLongitudeOfOrbitalPlane    ArgumentOfPerigee    MeanAnomaly    ZerothOrderClockCorrection    FirstOrderClockCorrection    SatelliteHealth    SatelliteConfiguration
    ____________________    _____________    ______________________    _________    ___    ________________    ____________    _________________    ____________________    ___________________    _________________________________    _________________    ___________    __________________________    _________________________    _______________    ______________________

    12-Apr-2022 16:50:54        2205               2.3347e+05              1        63            0                0.01171          0.014391            -2.4484e-09               5153.6                        -0.9271                      0.28359          -0.23387              0.00038624                    -7.276e-12                  0                     11          
    12-Apr-2022 16:50:54        2205               2.3347e+05              2        61            0               0.020515         0.0074596            -2.5029e-09               5153.6                       -0.95587                     -0.45355          -0.18869             -0.00065327                             0                  0                      9          
    12-Apr-2022 16:50:54        2205               2.3347e+05              3        69            0              0.0040326         0.0096912            -2.5757e-09               5153.6                       -0.59787                      0.29979          -0.59118             -0.00020409                   -1.4552e-11                  0                     11          
    12-Apr-2022 16:50:54        2205               2.3347e+05              4        74            0              0.0017715         0.0059814            -2.4665e-09               5153.6                       -0.25353                     -0.95004           0.31619             -0.00017643                     3.638e-12                  0                     12          
    12-Apr-2022 16:50:54        2205               2.3347e+05              5        50            0              0.0059118         0.0055599            -2.6193e-09               5153.6                       -0.61097                      0.32122           0.61334             -7.8201e-05                             0                  0                     10          
    12-Apr-2022 16:50:54        2205               2.3347e+05              6        67            0              0.0026565          0.014187             -2.452e-09               5153.7                       -0.92973                     -0.28158           -0.1523              0.00026417                    1.4552e-11                  0                     11          
    12-Apr-2022 16:50:54        2205               2.3347e+05              7        48            0               0.015865         0.0028152            -2.5138e-09               5153.6                        0.07053                     -0.72524          -0.44853              0.00032043                             0                  0                     10          
    12-Apr-2022 16:50:54        2205               2.3347e+05              8        72            0              0.0074387         0.0068531            -2.4738e-09               5153.7                        0.72894                     0.048076             0.467             -6.3896e-05                             0                  0                     11          
    12-Apr-2022 16:50:54        2205               2.3347e+05              9        68            0              0.0021076         0.0037479            -2.5029e-09               5153.5                       -0.27053                      0.59743           0.61325             -0.00034428                     3.638e-12                  0                     11          
    12-Apr-2022 16:50:54        2205               2.3347e+05             10        73            0              0.0075555         0.0096321            -2.5793e-09               5153.6                       -0.59875                     -0.79359          -0.88495              -0.0003767                   -1.0914e-11                  0                     11          
    12-Apr-2022 16:50:54        2205               2.3347e+05             11        78            0             0.00031376         0.0064716            -2.5393e-09               5153.7                        -0.9136                      0.85276           0.49013             -4.1962e-05                     7.276e-12                 63                     12          
    12-Apr-2022 16:50:54        2205               2.3347e+05             12        58            0              0.0087256          0.008585            -2.5575e-09               5153.5                        0.42482                      0.40497          -0.64747             -0.00019932                    -7.276e-12                  0                     10          
    12-Apr-2022 16:50:54        2205               2.3347e+05             13        43            0              0.0058503         0.0083656            -2.4374e-09               5153.6                       -0.22159                      0.29646           0.31699              0.00029278                     7.276e-12                  0                      9          
    12-Apr-2022 16:50:54        2205               2.3347e+05             14        77            0              0.0016966         0.0033073            -2.6121e-09               5153.6                        0.41456                      0.97049          -0.63662             -0.00010204                    -3.638e-12                  0                     12          
    12-Apr-2022 16:50:54        2205               2.3347e+05             15        55            0               0.013989         -0.003952            -2.5866e-09               5153.7                       -0.30476                      0.34521           0.16087             -6.9618e-05                     3.638e-12                  0                     10          
    12-Apr-2022 16:50:54        2205               2.3347e+05             16        56            0               0.012782         0.0085545            -2.5611e-09               5153.6                        0.43073                      0.23073           0.76066             -0.00049114                    -3.638e-12                  0                      9          
      ⋮

Get the satellite positions, velocities, and IDs at the first time step.

t = data.Time(1);
[satPos,satVel,satID] = gnssconstellation(t,data,GNSSFileType="SEM")

satPos = 31×3
107 ×

    1.3899   -2.2151    0.3074
   -1.6755    0.5872   -1.9147
    1.5377   -1.2781   -1.7528
    0.6332   -1.6385   -1.9887
   -2.5716    0.5413    0.4215
   -1.0251   -1.1336   -2.1646
    0.2694   -2.3585    1.1775
    1.3414   -0.7139    2.1761
   -0.3881   -2.2626   -1.3395
    1.5043    1.1879    1.8656
      ⋮

satVel = 31×3
103 ×

    0.0014    0.4854    3.2261
    0.8625   -2.4217   -1.4348
    2.2113    0.0321    1.9394
    1.4081    2.1049   -1.2936
   -0.5761   -0.2150   -3.1036
    1.2999   -2.4327    0.6643
    0.9229   -1.1620   -2.6758
    1.5581    2.2893   -0.1743
    1.1480    1.2668   -2.4877
   -2.3150    0.2417    1.6982
      ⋮

satID = 31×1

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      ⋮

Retrieve Satellite Positions, Velocities, and IDs from YUMA Almanac File

Read GPS navigation message data from a YUMA almanac file.

data = yumaread("yumaAlmanac_2022-9-27.alm")

data=31×13 timetable
            Time            PRN    Health    Eccentricity    TimeOfApplicability    OrbitalInclination    RateOfRightAscen    SQRTA     RightAscenAtWeek    ArgumentOfPerigee    MeanAnom        Af0           Af1        Week
    ____________________    ___    ______    ____________    ___________________    __________________    ________________    ______    ________________    _________________    ________    ___________    __________    ____

    29-Sep-2022 16:38:06     1       0          0.012008          4.055e+05              0.98891            -7.5432e-09       5153.6          0.3651              0.9438           -1.095     0.00027561    -7.276e-12    2229
    29-Sep-2022 16:38:06     2       0              0.02          4.055e+05              0.96685            -7.7946e-09       5154.9         0.27125              -1.393          -1.6195    -0.00064468             0    2229
    29-Sep-2022 16:38:06     3       0         0.0044999          4.055e+05              0.97519             -7.726e-09       5153.5          1.3977              1.0651          -2.1966    -0.00035858    -3.638e-12    2229
    29-Sep-2022 16:38:06     4       0         0.0020423          4.055e+05              0.96187             -7.966e-09       5153.7          2.4795             -3.1045          0.81839    -0.00011158     7.276e-12    2229
    29-Sep-2022 16:38:06     5       0         0.0060811          4.055e+05              0.96224            -7.8403e-09       5153.7          1.3543              1.1188            1.415    -9.8228e-05             0    2229
    29-Sep-2022 16:38:06     6       0         0.0024514          4.055e+05              0.98822            -7.5546e-09       5153.5         0.35683             -0.8974         -0.87447     0.00047684    1.0914e-11    2229
    29-Sep-2022 16:38:06     7       0          0.016406          4.055e+05              0.95104            -7.7832e-09       5153.6         -2.7871             -2.2412          -1.7241     0.00030327    -3.638e-12    2229
    29-Sep-2022 16:38:06     8       0         0.0075631          4.055e+05              0.96192            -8.2403e-09       5153.5        -0.71955             0.16395           1.1555    -8.6784e-05             0    2229
    29-Sep-2022 16:38:06     9       0         0.0025387          4.055e+05              0.95495            -8.0575e-09       5153.7          2.4248              1.9083           1.5732    -0.00028992     3.638e-12    2229
    29-Sep-2022 16:38:06    10       0         0.0079675          4.055e+05              0.97498            -7.7489e-09       5153.6           1.395             -2.5116          -3.0858     -5.722e-06             0    2229
    29-Sep-2022 16:38:06    11       0        0.00075054          4.055e+05              0.96415            -7.7832e-09       5153.6         0.40358             -3.1036          0.81271    -2.0981e-05    -3.638e-12    2229
    29-Sep-2022 16:38:06    12       0         0.0085082          4.055e+05              0.96755             -7.966e-09       5153.7         -1.6731              1.3158          -2.4318     -0.0002861    -7.276e-12    2229
    29-Sep-2022 16:38:06    13       0         0.0065126          4.055e+05              0.96921            -7.8518e-09       5153.6          2.5812             0.94039          0.67456     0.00039673     7.276e-12    2229
    29-Sep-2022 16:38:06    14       0          0.002305          4.055e+05              0.95095            -8.1261e-09       5153.6          -1.708             -3.0302          -2.4903    -0.00010014     3.638e-12    2229
    29-Sep-2022 16:38:06    15       0          0.014625          4.055e+05              0.93093            -8.3203e-09       5153.6          2.3127              1.1401          0.17435    -2.4796e-05     3.638e-12    2229
    29-Sep-2022 16:38:06    16       0          0.012809          4.055e+05              0.96738            -7.9889e-09       5153.7         -1.6547             0.73255           2.0697    -0.00052547             0    2229
      ⋮

Get the satellite positions, velocities, and IDs at the first time step.

t = data.Time(1);
[satPos,satVel,satID] = gnssconstellation(t,data,GNSSFileType="YUMA")

satPos = 31×3
107 ×

   -1.3549    2.2358   -0.3793
    1.4926   -2.1942   -0.1952
   -1.2477    1.2357   -2.0018
   -0.4096    2.0385   -1.6467
    2.2427   -0.7207    1.2218
    1.4711    0.4089   -2.1680
   -0.0841    2.0989    1.6373
   -1.0615    1.1949    2.1111
    0.5989    2.4816   -0.7333
   -1.9686   -1.1518    1.4018
      ⋮

satVel = 31×3
103 ×

   -0.4388    0.2295    3.2113
    0.0460    0.4065   -3.1646
   -2.4900   -0.3576    1.3500
   -0.9647   -1.8691   -2.0833
    1.5583    0.3175   -2.6224
   -1.6003    2.2475   -0.6531
   -1.3741    1.5034   -2.0994
   -1.2344   -2.3991    0.7711
   -0.6518   -0.7124   -2.9785
    1.7466    0.0160    2.4627
      ⋮

satID = 31×1

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      ⋮

Read Navigation Data from Galileo Almanac File

Read navigation data from a Galileo almanac file and use the navigation data to:

• Get satellite positions, velocities, and IDs at a given timestamp.

• Compute satellite visibility and look angles for a given receiver position by using the extracted satellite positions.

First, read GPS navigation message data from a Galileo almanac file.

filename = "galAlmanac_2019-08-06.xml";
data = galalmanacread(filename)

data=22×16 timetable
            Time            SVID    aSqRoot        ecc          deltai       omega0      omegaDot         w           m0            af0            af1        iod       t0a       wna     statusE5a    statusE5b    statusE1B
    ____________________    ____    ________    __________    __________    ________    ___________    ________    _________    ___________    ___________    ___    _________    ____    _________    _________    _________

    06-Aug-2019 08:39:42      1     0.011719    0.00022888     0.0030518    -0.11984    -1.8626e-09    -0.81259    -0.053925    -0.00066185     -7.276e-12     4      2.04e+05    1041        0            0            0    
    06-Aug-2019 08:39:42      2     0.017578    0.00010681     0.0030518    -0.11984    -1.8626e-09    -0.50497      0.63766     7.2479e-05              0     4      2.04e+05    1041        0            0            0    
    06-Aug-2019 08:39:42      3     0.042969    0.00036621    -0.0076904    -0.78656    -1.7462e-09     -0.1449      0.94464    -0.00019646     -3.638e-12     4      2.04e+05    1041        0            0            0    
    06-Aug-2019 08:39:42      4     0.039062    0.00027466    -0.0076904    -0.78653    -1.7462e-09    -0.40698    -0.041412    -0.00033951     -7.276e-12     4      2.04e+05    1041        0            0            0    
    06-Aug-2019 08:39:42      5     0.042969    0.00021362    -0.0076904    -0.78656    -1.7462e-09    -0.33777     -0.61145    -0.00045967      3.638e-12     4      2.04e+05    1041        0            0            0    
    06-Aug-2019 08:39:42      7     0.042969    0.00041199    -0.0076904    -0.78656    -1.7462e-09      -0.285      0.58496    -0.00024033     -7.276e-12     4      2.04e+05    1041        0            0            0    
    06-Aug-2019 08:39:42      8     0.039062    0.00036621    -0.0057983      -0.789    -1.7462e-09    -0.19412      0.74414      0.0063114     -7.276e-12     4      2.04e+05    1041        0            0            0    
    06-Aug-2019 08:39:42      9     0.039062    0.00045776    -0.0057983      -0.789    -1.7462e-09    -0.21506      -0.4855      0.0063572    -1.0914e-11     4      2.04e+05    1041        0            0            0    
    06-Aug-2019 08:39:42     11     0.017578    0.00038147     0.0021973     0.54333    -1.7462e-09     0.28098      -0.3125      0.0056324    -1.0914e-11     4      2.04e+05    1041        0            0            0    
    06-Aug-2019 08:39:42     12     0.015625     0.0002594     0.0021973     0.54333    -1.7462e-09     0.10056      0.12363      0.0062618     -1.819e-11     4      2.04e+05    1041        0            0            0    
    06-Aug-2019 08:39:42     13     0.021484    1.5259e-05     0.0032349     0.54181    -1.7462e-09     0.23178      0.73837     0.00039101              0     4      2.04e+05    1041        0            0            0    
    06-Aug-2019 08:29:42     15     0.017578    3.0518e-05     0.0032349     0.54178    -1.7462e-09    -0.60843     -0.19565     0.00090027              0     3     2.034e+05    1041        0            0            0    
    06-Aug-2019 08:39:42     19     0.027344    0.00024414    -0.0058594    -0.78732    -1.7462e-09    -0.47565      0.30069    -3.8147e-06              0     4      2.04e+05    1041        0            0            0    
    06-Aug-2019 08:39:42     21     0.021484    0.00022888     0.0029297    -0.12067    -1.8626e-09    -0.91656      0.30164    -0.00054741     -3.638e-12     4      2.04e+05    1041        0            0            0    
    06-Aug-2019 08:39:42     24     0.011719    0.00024414     0.0022583    -0.11884    -1.8626e-09     0.27414      0.35886      0.0059395     -1.819e-11     4      2.04e+05    1041        0            0            0    
    06-Aug-2019 08:39:42     25     0.027344    0.00032043     0.0029297     -0.1207    -1.8626e-09     -0.7215     -0.89252      0.0017204    -1.0914e-11     4      2.04e+05    1041        0            0            0    
      ⋮

Specify the timestamp for which to find the satellite positions, velocities, and IDs.

t = datetime(2021,06,24,01,59,44)

t = datetime
   24-Jun-2021 01:59:44

Get the satellite positions, velocities, and IDs at the specified timestamp by using the gnssconstellation function.

[satPos,satVel,satID] = gnssconstellation(t,data,GNSSFileType="galalmanac");

Specify a receiver position in geodetic coordinates (latitude, longitude, altitude) to compute the satellite look angles and visibility.

recPos = [42.3013162 -71.3782972 0];

Specify the elevation mask angle for the receiver.

maskAngle = 5;

Compute the look angles and visibilities of satellite positions for the given receiver position. The vis output indicates which satellites are visible. Get the total using nnz.

[az,el,vis] = lookangles(recPos,satPos,maskAngle);
fprintf('%d satellites visible at %s.\n',nnz(vis),t)

10 satellites visible at 24-Jun-2021 01:59:44.

Plot the visible satellite positions with the elevation mask.

figure
skyplot(az(vis),el(vis),satID(vis),MaskElevation=maskAngle)

Input Arguments

t — Current time for satellite simulation

scalar datetime array

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 January 6, 1980 at 00:00 (UTC). Specifying any datetime prior to this time will use the GPS start time.

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

Data Types: datetime

navData — Navigation data

timetable

Navigation data, specified as a timetable.

• For a RINEX file, you can obtain the timetable from the structure returned by the rinexread function.

• For a SEM almanac file, you can use the timetable returned by the semread function.

• For a YUMA almanac file, you can use the timetable returned by the yumaread function.

• For a Galileo XML almanac file, you can use the timetable returned by the galalmanacread function.

Read Navigation Data from RINEX File

The gnssconstellation function can process the GPS or Galileo data read from a RINEX file. The contents of the structure returned by the rinexread function vary depending on the type of satellite system described by the RINEX file. For more information on the contents of the structure, see the rinexread function More About section.

To read GPS navigation message data from a RINEX file, extract the GPS field from the returned structure. For example:

rinexData = rinexread("GODS00USA_R_20211750000_01D_GN.rnx");
navData = rinexData.GPS;

To read Galileo navigation message data from a RINEX file, extract the Galileo field from the returned structure. For example:

rinexData = rinexread("GODS00USA_R_20211750000_01D_EN.rnx");
navData = rinexData.Galileo;

To read GLONASS navigation message data from a RINEX file, extract the GLONASS field from the returned structure. For example:

rinexData = rinexread("GODS00USA_R_20211750000_01D_RN.rnx");
navData = rinexData.GLONASS;

To read BeiDou navigation message data from a RINEX file, extract the BeiDou field from the returned structure. For example:

rinexData = rinexread("GODS00USA_R_20211750000_01D_CN.rnx");
navData = rinexData.BeiDou;

To read NavIC/IRNSS navigation message data from a RINEX file, extract the NavIC field from the returned structure. For example:

rinexData = rinexread("ARHT00ATA_R_20211750000_01D_IN.rnx");
navData = rinexData.NavIC;

To read QZSS navigation message data from a RINEX file, extract the QZSS field from the returned structure. For example:

rinexData = rinexread("ARHT00ATA_R_20211750000_01D_JN.rnx");
navData = rinexData.QZSS;

To read SBAS navigation message data from a RINEX file, extract the SBAS field from the returned structure. For example:

rinexData = rinexread("GOP600CZE_R_20211750000_01D_SN.rnx");
navData = rinexData.SBAS;

Read Navigation Data from SEM Almanac File

The gnssconstellation function can process the GPS data read from a SEM almanac file. The timetable returned by the semread function contains the parameters of each satellite in the almanac file associated with the specified date. For more information on the contents of the timetable, see the data argument of the semread function.

Because semread returns a timetable, you can directly specify navData as the semread output argument. For example:

navData = semread("semalmanac_2022-1-18.al3")

Read Navigation Data from YUMA Almanac File

The gnssconstellation function can process the GPS and QZSS data read from a YUMA almanac file. The timetable returned by the yumaread function contains the parameters of each satellite in the almanac file associated with the specified date. For more information on the contents of the timetable, see the data argument of the yumaread function.

Because yumaread returns a timetable, you can directly specify navData as the yumaread output argument. For example:

navData = yumaread("yumaAlmanac_2022-4-20.alm")

Read Navigation Data from Galileo XML Almanac File

The gnssconstellation function can process the Galileo data read from a Galileo XML almanac file. The timetable returned by the galalmanacread function contains the parameters of each satellite in the almanac file associated with the specified date. For more information on the contents of the timetable, see the data argument of the galalmanacread function.

Because galalmanacread returns a timetable, you can directly specify navData as the galalmanacread output argument. For example:

navData = galalmanacread("galAlmanac_2023-02-17.xml")

Note

• When you read Galileo data in RINEX format, the week number is aligned with the GPS week. The GPS time of week starts at the midnight between 5th and 6th January 1980.

  When you read Galileo data in Almanac format, the week number is aligned with the Galileo system time (GST). The GST start epoch is 13 seconds before 00:00 UTC on Sunday 22nd August 1999 (midnight between 21st and 22nd August).

gnssFileType — GNSS file type

"RINEX" | "SEM" | "YUMA" | "galalmanac"

GNSS file type, specified as "RINEX", "SEM", "YUMA", or "galalmanac".

Specify the GNSS file type as,

• "RINEX" when specifying the navigation data as a timetable obtained from the structure returned by the rinexread function.

• "SEM" when specifying the navigation data as a timetable returned by the semread function.

• "YUMA" when specifying the navigation data as a timetable returned by the yumaread function.

• "galalmanac" when specifying the navigation data as a timetable returned by the galalmanacread function.

Example: GNSSFileType="RINEX"

Example: GNSSFileType="SEM"

Example: GNSSFileType="YUMA"

Example: GNSSFileType="galalmanac"

Data Types: char | string

Output Arguments

satPos — Satellite positions

N-by-3 matrix of scalars

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

satVel — Satellite velocities

N-by-3 matrix of scalar

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

satID — Satellite identification numbers

N-element column vector

Satellite identification numbers, returned as an N-element column vector. N is the number of satellites in the constellation.

Data Types: single | double

More About

Orbital Parameters

Orbital parameters define the initial positions and velocities of a satellite and enable you to calculate past and future positions and velocities of the satellites based on those initial positions and velocities. These orbital parameters produce accurate results within a time range of the time of ephemeris, or initial time for satellites that do not record time of ephemeris. To get accurate position and velocity calculations, ensure that you are using the correct orbital parameters for the corresponding querying time.

These are the time windows in which the orbital parameters are valid for position and velocity calculations:

• GPS, Galileo, BeiDou, NavIC, QZSS — [t_i-2 hours, t_i+2 hours].

• GLONASS, SBAS — [t_i-15 minutes, t_i+15 minutes].

t_i is the time of ephemeris or initial time for satellites that do not record time of ephemeris.

For GPS, Galileo, BeiDou, NavIC, and QZSS satellites, Table A.2-2 in GPS SPS Performance Standard defines the satellite positions and velocities in Earth-centered Earth-fixed (ECEF) coordinates. Position calculations use equations from Table 30-II in the same IS-GPS-200M Interface Specification. Velocity calculations use equations 8.21–8.27 in Principles of GNSS, Inertial, and Multisensor Integrated Navigation Systems [1].

For GLONASS, and SBAS satellites, Section A.3.1.2 in GLONASS ICD Edition 5.1 2008 defines equations for both the positions and velocities in Earth-centered Earth-fixed (ECEF) coordinates.

References

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

[2] International GNSS Service (IGS), Daily 30-Second GPS Broadcast Ephemeris Data, NASA Crustal Dynamics Data Information System (CDDIS), Greenbelt, MD, USA, Jun. 24, 2021. Accessed Jun. 25, 2021. https://dx.doi.org/10.5067/GNSS/gnss_daily_n_001.

[3] United States Coast Guard. "GPS Almanacs, NANUs, and OPS Advisories Archives." US Coast Guard Navigation Center. Accessed May 6, 2022. https://www.navcen.uscg.gov/archives.

[4] QZSS almanac archives, Quasi-Zenith Satellite System(QZSS). "QZSS (Quasi-Zenith Satellite System) - Cabinet Office (Japan)" Accessed September 20, 2022. https://sys.qzss.go.jp/dod/en/archives/pnt.html.

[5] European GNSS Service Centre (GSC). "Galileo Open Service Signal-In-Space Interface Control Document." Accessed March 13, 2023. https://www.gsc-europa.eu/sites/default/files/sites/all/files/Galileo_OS_SIS_ICD_v2.1.pdf.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Only MEX functions are supported for code generation.

Version History

Introduced in R2021a

R2024a: Read navigation data from additional GNSS satellites

Read navigation data from a RINEX file containing these additional GNSS satellites:

• GLONASS

• BeiDou

• NavIC

• QZSS

• SBAS

See the navData argument for examples of how to read data from these satellites from RINEX files.

R2023b: Read data from Galileo XML almanac files

Specify input argument gnssFileType as "galalmanac" if the input navigation data navData is read from Galileo XML almanac file.