Find higher value with respect to time from a table?
Show older comments
With repect to time, i need higher value from the attached table.
Accepted Answer
William Rose
on 3 Sep 2023
Edited: William Rose
on 3 Sep 2023
[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)))
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.
10 Comments
SOMNATH MAHATO
on 3 Sep 2023
William Rose
on 3 Sep 2023
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
on 4 Sep 2023
William Rose
on 4 Sep 2023
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
on 4 Sep 2023
William Rose
on 4 Sep 2023
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
on 4 Sep 2023
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)])
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)])
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
on 5 Sep 2023
William Rose
on 5 Sep 2023
@SOMNATH MAHATO, you are welcome.
More Answers (2)
Convert data into an easier to read format
!unzip 139.zip
!head 139.txt
!sed -i 's/ */,/g' 139.txt
!sed -i 's/EL(deg) SNR(dBHz)/EL(deg),SNR(dBHz)/g' 139.txt
!head 139.txt
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)
Find the maximum elevation angle for each row time using groupsummary
groupsummary(tt,"% TIME (GPST)","max","EL(deg)")
William Rose
on 31 Aug 2023
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.
4 Comments
SOMNATH MAHATO
on 3 Sep 2023
William Rose
on 3 Sep 2023
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
on 3 Sep 2023
SOMNATH MAHATO
on 3 Sep 2023
Categories
Find more on Reference Applications in Help Center and File Exchange
Products
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
