Find higher value with respect to time from a table?

With repect to time, i need higher value from the attached table.

Answer 1

[William Rose]

@SOMNATH MAHATO,

[Edit: add code to display satellite at maxAz and satellite at maxEl.)

I understand now that you wish to find the max azimuth and max elevation within a specified time window. You can do it as follows:

T=readtable('data139a.txt');                % read tabular data from file
dt=datetime(T.(1),'InputFormat','yyyy/MM/dd')+T.(2);   % make a datetime vector
% Combine datetime vector with the other columns to make a timetable. 
TT=timetable(dt,T.(3),T.(4),T.(5),T.(6),T.(7));        % make a timetable
% Extract all rows within specified time range:
dt1=datetime('19-May-2022 12:00:00');       % dt1=start datetime
dt1s=string(dt1,'HH:mm:ss');                % string for dt1
dt2=datetime('19-May-2022 12:00:30');       % dt2=end datetime
dt2s=string(dt2,'HH:mm:ss');                % string for dt2
TTsmall=TT(dt>=dt1 & dt<dt2,:);             % timetable with dt1<=datetime<dt2
% Find the max Az and max EL, in the specified time range
[maxAZ,maxAZidx]=max(TTsmall.Var2);
[maxEL,maxELidx]=max(TTsmall.Var3);
% Use maxAZidx or maxELidx to find other properties associated with the
% maximum, such as satellite name, SNR at max El, etc.
% Display results
fprintf('Total table rows: %d.\n',height(TT)); ...
fprintf('%d table rows have %s<=datetime<%s.\n',height(TTsmall),dt1s,dt2s);...
fprintf('%s<=time<%s:\n',dt1s,dt2s); ...
fprintf('Max AZ=%.1f, satellite %s\n',maxAZ,string(TTsmall.Var1(maxAZidx))); ...
fprintf('Max EL=%.1f, satellite %s\n',maxEL,string(TTsmall.Var1(maxELidx)))

Total table rows: 8346.

3 table rows have 12:00:00<=datetime<12:00:30.

12:00:00<=time<12:00:30:

Max AZ=249.1, satellite G10

Max EL=20.3, satellite G10

The code above finds the max azimuth and max elevation within a specfied time window, and displays the results. There are other ways to do it, which would have fewer lines of code.

Good luck.

[SOMNATH MAHATO]

I have run this code and found an error. I have attached the schreenshot of the error.

[William Rose]

The code failed because the file data139a.txt was not in a directory that Matlab looks in. Please download the file data139a.txt from our Matlab Answers discussion, and put in in the same directory as your script. Or change the change line 1 of the script to

T=readtable('139.txt');

to read your original file, and make sure 139.txt is in the same directory as your script, or add its directory to the Matlab path.

[SOMNATH MAHATO]

Thank you for your support. How can i get continoues time series of the data?

For example:

Time Max Azimuth Maz Elevation

00:00:00

00:00:30

00:01:00

..............

23:59:30

[William Rose]

@SOMNATH MAHATO,

Make a for loop. On each loop pass, change dt1 and dt2, and find the max Az and Max El using the ideas in the code above. Store the results from each loop pass in an array.

[SOMNATH MAHATO]

I have tried but it hasn't work. Can you help me?

[William Rose]

@SOMNATH MAHATO,

Please share what you have tried. Please explain how it did not work. I get better at coding by trying, failing, and trying again.

[SOMNATH MAHATO]

Thank you for your suggestion. I am also tried to learn matlab. I will remainber your advise.

Find my changes in the code

T=readtable('139.txt'); % read tabular data from file

dt=datetime(T.(1),'InputFormat','yyyy/MM/dd')+T.(2); % make a datetime vector

% Combine datetime vector with the other columns to make a timetable.

TT=timetable(dt,T.(3),T.(4),T.(5),T.(6),T.(7)); % make a timetable

% Extract all rows within specified time range:

dt1=datetime('19-May-2022 00:00:00'); % dt1=start datetime

dt1s=string(dt1,'hh:mm:ss'); % string for dt1

dt2=datetime('19-May-2022 11:59:30'); % dt2=end datetime

dt2s=string(dt2,'hh:mm:ss'); % string for dt2

TTsmall=TT(dt>=dt1 & dt<dt2,:); % timetable with dt1<=datetime<dt2

% Find the max Az and max EL, in the specified time range

for dt=1:104001

plot(dt1.(3),dt2.(4))

end

[~,maxAZidx]=max(TTsmall.Var2);

[~,maxELidx]=max(TTsmall.Var3);

maxAZ=TTsmall.Var2(maxAZidx);

maxEL=TTsmall.Var3(maxELidx);

% Display results

fprintf('Total table rows: %d.\n',height(TT)); ...

fprintf('Table rows with %s<=datetime<%s: %d.\n',dt1s,dt2s,height(TTsmall));...

fprintf('For %s<=time<%s, max AZ=%.1f, max EL=%.1f.\n',dt1s,dt2s,maxAZ,maxEL)

[William Rose]

@SOMNATH MAHATO,

Make a vector of starting times for each interval, as follows:

dt1=datetime('19-May-2022')+seconds(0:30:86370);

Confirm that the start times are what you want:

disp([dt1(1),dt1(2),dt1(end-1),dt1(end)])

   19-May-2022 00:00:00   19-May-2022 00:00:30   19-May-2022 23:59:00   19-May-2022 23:59:30

Make a vector of ending times for each interval as follows:

dt2=dt1+seconds(30);

Confirm that the end times are what you want:

disp([dt2(1),dt2(2),dt2(end-1),dt2(end)])

   19-May-2022 00:00:30   19-May-2022 00:01:00   19-May-2022 23:59:30   20-May-2022 00:00:00

Inside the for loop, use dt1(i) and dt2(i) to define the time interval to search.

The earlier script created a small timetable with the rows in the specified time interval. Then I found the max Az and max El, in the small timetable.

%earlier script
TTsmall=TT(dt>=dt1 & dt<dt2,:);             % timetable with dt1<=datetime<dt2
[maxAZ,maxAZidx]=max(TTsmall.Var2);
[maxEL,maxELidx]=max(TTsmall.Var3);

The new script does not create a small timetable. It finds the maximum within the rows of the big timetable whose times are within the interval. Also, the new script does not need the indices, so I do not find them.

% new script
maxAz(i)=max(TT.Var2(dt>=dt1(i) & dt<dt2(i)));
maxEL(i)=max(TT.Var3(dt>=dt1(i) & dt<dt2(i)));

The full script is attached. It creates the following output on the colsole:

>> satelliteAzEl

Total table rows: 104002, intervals=2880.

>>

It also makes the plot below:

The satellite with max elevation at a given time is usually different than the the satellite with maximum azimuth at the same time.

Good luck.

[SOMNATH MAHATO]

Thank you for your continous support and help.

[William Rose]

@SOMNATH MAHATO, you are welcome.

Answer 2

[Seth Furman]

Convert data into an easier to read format

!unzip 139.zip

Archive:  139.zip
  inflating: 139.txt                 

!head 139.txt

% TIME (GPST)            SAT  AZ(deg)  EL(deg) SNR(dBHz)   L1 MP(m)
2022/05/19 00:34:30.0    G01    146.7     15.6     28.50     0.0000
2022/05/19 00:39:00.0    G01    144.9     16.4     31.31     0.0000
2022/05/19 00:40:00.0    G01    144.4     16.6     31.81     0.0000
2022/05/19 00:43:30.0    G01    143.0     17.2     32.44     0.0000
2022/05/19 00:44:00.0    G01    142.8     17.3     34.13     0.3673
2022/05/19 00:44:30.0    G01    142.6     17.4     31.69     0.4631
2022/05/19 00:45:00.0    G01    142.4     17.5     32.88     1.2921
2022/05/19 00:45:30.0    G01    142.2     17.6     32.06    -0.1025
2022/05/19 00:46:00.0    G01    142.0     17.7     30.66     1.2019

!sed -i 's/   */,/g' 139.txt
!sed -i 's/EL(deg) SNR(dBHz)/EL(deg),SNR(dBHz)/g' 139.txt
!head 139.txt

% TIME (GPST),SAT,AZ(deg),EL(deg),SNR(dBHz),L1 MP(m)
2022/05/19 00:34:30.0,G01,146.7,15.6,28.50,0.0000
2022/05/19 00:39:00.0,G01,144.9,16.4,31.31,0.0000
2022/05/19 00:40:00.0,G01,144.4,16.6,31.81,0.0000
2022/05/19 00:43:30.0,G01,143.0,17.2,32.44,0.0000
2022/05/19 00:44:00.0,G01,142.8,17.3,34.13,0.3673
2022/05/19 00:44:30.0,G01,142.6,17.4,31.69,0.4631
2022/05/19 00:45:00.0,G01,142.4,17.5,32.88,1.2921
2022/05/19 00:45:30.0,G01,142.2,17.6,32.06,-0.1025
2022/05/19 00:46:00.0,G01,142.0,17.7,30.66,1.2019

Read data into a timetable

opts = detectImportOptions("139.txt",ReadVariableNames=true,NumHeaderLines=0,VariableNamingRule="preserve",TextType="string");
opts = setvaropts(opts,"% TIME (GPST)",Type="datetime",InputFormat="uuuu/MM/dd HH:mm:ss.S");
tt = readtimetable("139.txt",opts)

tt = 104002×5 timetable
        % TIME (GPST)         SAT     AZ(deg)    EL(deg)    SNR(dBHz)    L1 MP(m)
    _____________________    _____    _______    _______    _________    ________

    2022/05/19 00:34:30.0    "G01"     146.7      15.6         28.5            0 
    2022/05/19 00:39:00.0    "G01"     144.9      16.4        31.31            0 
    2022/05/19 00:40:00.0    "G01"     144.4      16.6        31.81            0 
    2022/05/19 00:43:30.0    "G01"       143      17.2        32.44            0 
    2022/05/19 00:44:00.0    "G01"     142.8      17.3        34.13       0.3673 
    2022/05/19 00:44:30.0    "G01"     142.6      17.4        31.69       0.4631 
    2022/05/19 00:45:00.0    "G01"     142.4      17.5        32.88       1.2921 
    2022/05/19 00:45:30.0    "G01"     142.2      17.6        32.06      -0.1025 
    2022/05/19 00:46:00.0    "G01"       142      17.7        30.66       1.2019 
    2022/05/19 00:46:30.0    "G01"     141.8      17.8        32.03      -0.2771 
    2022/05/19 00:47:00.0    "G01"     141.6      17.9        32.06      -0.8351 
    2022/05/19 00:47:30.0    "G01"     141.4        18        31.38      -0.3719 
    2022/05/19 00:48:00.0    "G01"     141.2      18.1        33.31      -0.1552 
    2022/05/19 00:48:30.0    "G01"       141      18.2        33.38       0.7502 
    2022/05/19 00:49:00.0    "G01"     140.8      18.3        35.44        0.311 
    2022/05/19 00:49:30.0    "G01"     140.6      18.4        33.53       0.0172 

Find the maximum elevation angle for each row time using groupsummary

groupsummary(tt,"% TIME (GPST)","max","EL(deg)")

ans = 2880×3 table
        % TIME (GPST)        GroupCount    max_EL(deg)
    _____________________    __________    ___________

    2022/05/19 00:00:00.0        34           74.5    
    2022/05/19 00:00:30.0        35           74.7    
    2022/05/19 00:01:00.0        34           74.9    
    2022/05/19 00:01:30.0        34             75    
    2022/05/19 00:02:00.0        35           75.2    
    2022/05/19 00:02:30.0        35           75.3    
    2022/05/19 00:03:00.0        34           75.5    
    2022/05/19 00:03:30.0        35           75.7    
    2022/05/19 00:04:00.0        35           75.8    
    2022/05/19 00:04:30.0        35             76    
    2022/05/19 00:05:00.0        34           76.1    
    2022/05/19 00:05:30.0        35           76.3    
    2022/05/19 00:06:00.0        33           76.4    
    2022/05/19 00:06:30.0        34           76.6    
    2022/05/19 00:07:00.0        34           76.7    
    2022/05/19 00:07:30.0        34           76.9    

Answer 3

[William Rose]

@SOMNATH MAHATO

Please explain exactly what you want to do in more detail. Provide an example of code you have tried that did not work.

Your file has 104,002 rows of data, which are observations of about 113 satellites.* The data is sorted by satellite and then by time. I have attached a shorter file with data from 10 satellites, to demonstrate code. Column 1=date, column 2=time of day. The observation times vary for different satelites. Some times are repeated many times through the table. All observations are on the same date.

Combine the date and time columns, to make a datetime array.

T=readtable('data139a.txt');
dt1=datetime(T.(1),'InputFormat','yyyy/MM/dd')+T.(2);   % make a datetime vector

Combine the datetime array with the other columns to make a timetable.

TT=timetable(dt1,T.(3),T.(4),T.(5),T.(6),T.(7));        % make a timetable

Extract all rows that have a time greater than a specified time:

dtref=datetime('19-May-2022 11:59:59');     % dtref=reference datetime
TTpm=TT(dt1>dtref,:);                       % timetable with all times greater than dtref

To make a timetable containing the data for just one satellite (satellite G01, in this example), do this:

TTg01=TT(strcmp(TT.(1),'G01'),:);           % timetable for satellite G01

*Satellites in file 139.txt: G01-G32, R01-R15, R17-R18, R20-R24, E01-E05, E07-E15, E18-E21, E24-E27, E30-E31, E33-E34, E36, J02-J04, J07, C19-C46.

[SOMNATH MAHATO]

Dear Rose,

Thank you for your support. I need maximum value with respect to time.

In the data set, every 30 second interval data are avalibale. how i can find max azimumth, max elevation with respect to time from all the satellites.

[William Rose]

@SOMNATH MAHATO,

Do you want to find the max azimiuth and max elevation for each satellite?

Why do you want to find max azimuth? I am asking that quesiton because it seems to me that max azimuth is an unusual quantity to seek to know. The max azimuth probably occurs as the satellite is crossing a threshold of visibility or signal strength.

Some of the satellites in the record make multiple passes, and some do not. If you wan thte max for each pass you will have to add some code to identify separate passes.

[SOMNATH MAHATO]

Dear Rose, I don't want get each satellite maximum elevation angle. I just want maximum elevation angle of a particular time.

[SOMNATH MAHATO]

For example, 00:00:00 time maximum elevation angle among all the satellite data present.