Sort satellites in Satellite Communication Toolbox

I take satellite information from TLE file, which contains information about 500+ satellites.

Can I show in satelliteScenarioViewer only satellites with Orbital Position > 50?

How can I do it?

Answer 1

[akshatsood]

Hi @Dl,

I understand that you seek guidance in shortlisting the satellites based on a particular condition i.e. orbital inclination greater than 20 degrees. To display only these satellites in the Satellite Scenario Viewer, it requires parsing the TLE file to extract orbital parameters, identify the satellites that satisfy the inclination criteria, and then selectively visualize those specific satellites in the scenario viewer.

Following Step 2, where I have applied filters to isolate satellites that meet the specific criteria, I proceed to Step 4. In this step, I process each of the shortlisted satellites. For each one, I determine its precise location within the input file (`file.txt`), then proceed to record not only the satellite's name but also the subsequent two lines of data into the output file (`filteredSatellites.txt`). This output file is then passed on to the "scenarioViewer" function for visualiztion purpose.

Here is a MATLAB code snippet that demonstrates the process

% Step 1: read the TLE file and parse it
tleData = tleread('file.txt');

% Step 2: filter satellites based on inclination
selectedSatellites = {};

for i = 1:length(tleData)
    inclination = tleData(i).Inclination;
    if inclination > 20
        selectedSatellites{end+1} = tleData(i);
    end
end

% Step 3: create a satellite scenario
startTime = datetime(2023, 1, 1, 0, 0, 0);
stopTime = startTime + days(1);
sampleTime = 60; % in seconds

sc = satelliteScenario(startTime, stopTime, sampleTime);

% Step 4: write selected satellites to a txt file
outputFile = "filteredSatellites.txt";
out = fopen(outputFile, 'w');

for i = 1:length(selectedSatellites)
    
    % extract name for the satellite
    satelliteName = selectedSatellites{i}.Name;
    
    % writeNextTwoLines locates the position of selectedSatellite 
    % within the input file 'file.txt'
    writeNextTwoLines = false;
    linesToWrite = 2;

    f = fopen('file.txt', 'r');

    while ~feof(f)
        currLine = fgets(f);

        if contains(currLine, satelliteName)           
            fprintf(out, '%s\n', satelliteName);  
            writeNextTwoLines = true;
            continue
        end

        % selected satellite is found then, and the next two 
        % lines are written to the output file
        if writeNextTwoLines & linesToWrite
            fprintf(out, '%s', currLine);
            linesToWrite = linesToWrite - 1;
        end
    end
    
    fclose(f);
end

fclose(out);

sat = satellite(sc, 'filteredSatellites.txt');

% Step 5: visualization
viewer = satelliteScenarioViewer(sc);

Have a look at the following references for a better understanding

https://in.mathworks.com/help/aerotbx/ug/tleread.html

I hope this helps.

[Dl]

What is TLELines?

My file is .txt, is it a problem?

[Dl]

tleData = tleread("tle.txt");

Error using tleread
Unable to create Two-Line Element (TLE) structure because the file 'tle.txt' was not found.

selectedSatellites = {};

for i = 1:length(tleData)
    
    year = tleData(i).Epoch.Year - 2000;
    frac_day = tleData(i).Epoch.Day + days(duration(tleData(i).Epoch.Hour,tleData(i).Epoch.Minute,tleData(i).Epoch.Second));

    julian_date = 2451544.5 + 365 * year + floor(0.25 * year) + floor(0.01 * year) + floor(0.0025 * year) + frac_day;
    julian_centuries = (julian_date - 2451545) / 36525;
    earth_rotation_angle = mod(2 * pi * (0.779057273264 + 0.00273781191135448 * julian_centuries * 36525 + (mod(julian_centuries * 36525,1))), 2 * pi);
    
    if earth_rotation_angle < 0
        earth_rotation_angle = 2 * pi + earth_rotation_angle;
    end

    gmst = mod((earth_rotation_angle + (0.014506 + 4612.15739966 * julian_centuries + 1.39667721 * julian_centuries * 10e2 - 0.00009344 * julian_centuries* 10e3 + 0.00001882 * julian_centuries * 10e4) / 60 / 60 * pi / 180) ,(2 *pi));

    if gmst < 0
        gmst = 2 * pi + gmst;
    end

    vernal_equinox = -gmst * 180 / pi;

    orb_pos = round(mod(tleData(i).RightAscensionOfAscendingNode + tleData(i).ArgumentOfPeriapsis + tleData(i).MeanAnomaly + vernal_equinox, 360));
    
    if orb_pos > 180
        orb_pos = orb_pos - 360
    else
        orb_pos
    end
    
    if orb_pos > 175
        selectedSatellites{end+1} = tleData(i);
    end
end

sc = satelliteScenario();


for i = 1:length(selectedSatellites)
    satn = satellite(sc, selectedSatellites{i}.TLELines);
end

satelliteScenarioViewer(sc);

This is my code and it doesn't work :(

[akshatsood]

Hi @Dl, could you please help me with the "tle.txt" file, it will allow me to reproduce the issue at my end and address the problem you are facing.

[Dl]

Hi

It's just really .txt file with text like this

It contains more satellites but looks exactly the same way

TDRS 5                  
1 21639U 91054B   24010.68729772  .00000098  00000+0  00000+0 0  9990
2 21639  14.1828   0.2823 0025271 355.3430 194.2333  1.00273517118799
IUS R/B(1)              
1 21640U 91054C   24010.66407335  .00014000  00000+0  29686-2 0  9990
2 21640  26.3989 148.1621 6726049 148.4213 280.2536  3.00852110312745
IUS R/B(2)              
1 21641U 91054D   24010.09670545  .00000106  00000+0  00000+0 0  9991
2 21641  14.7247 340.3842 0034282 326.2724  55.5420  1.00175445 38458

[akshatsood]

Hi @Dl,

Based on the details you have provided, I have refined the method to process a TXT file and extract specific satellite data according to the set criteria. Concerning the error mentioned in your comments, it appears that the file you are trying to read cannot be located at the specified path. To resolve this, please double-check the file name and confirm that the path is correctly specified when using the `tleread` function.

I have successfully applied the revised technique to the TXT file you supplied. I have included comments within the code to aid your understanding of the approach. Should you encounter any difficulties or require further clarification on the procedure, please let me know.

[Dl]

Wow, it literally should work but it gives me this mistake in the end of the code.

Error using feof
Invalid file identifier. Use fopen to generate a valid file identifier.

But everything is right according to MathHelp...

[akshatsood]

Could you please verify the file's location that you are re attempting to access? The error you are encountering typically occurs when the specified file cannot be located, or the file name has been incorrectly entered. Make sure the file path is correct and that the file name is spelled accurately.

https://in.mathworks.com/matlabcentral/answers/275360-error-using-feof-invalid-file-identifier-use-fopen-to-generate-a-valid-file-identifier?s_tid=ta_ans_results

[Dl]

I get f = -1, but

If I change

f = fopen('file.txt', 'r');

to

f = fopen('filteredSatellites.txt', 'r');

so I get f = 25, but then I get a mistake in

currLine = fgets(f);

currLine = -1 here

[akshatsood]

This will be your 'file.txt'. Whatever is the name at your side for this file, do replace it and proceed with the approach.

TDRS 5                  
1 21639U 91054B   24010.68729772  .00000098  00000+0  00000+0 0  9990
2 21639  14.1828   0.2823 0025271 355.3430 194.2333  1.00273517118799
IUS R/B(1)              
1 21640U 91054C   24010.66407335  .00014000  00000+0  29686-2 0  9990
2 21640  26.3989 148.1621 6726049 148.4213 280.2536  3.00852110312745
IUS R/B(2)              
1 21641U 91054D   24010.09670545  .00000106  00000+0  00000+0 0  9991
2 21641  14.7247 340.3842 0034282 326.2724  55.5420  1.00175445 38458

[Dl]

Thank You so much!

Now it works!

I'm really new in MatLab and didn't do any studies before, it was so unexpected

You helped me very very much!