I want to read an Ionex file from CDDIS in MATLAB that I have a TEC map that is plotted as a TEC image

The ionox file has TEC values for each latitude over a longitudinal band from -180 to 180 in each latitudinal compartment. But also, this is also in a compartment for a single hour (1), this repeats itself for 24 times to fill 24 hours, the file is attached as c2.txt. The output should be in this format, attached as outfile.txt

Answer 1

[Paras Gupta]

Hi Rukundo,

I understand that you want to read the given IONEX file, process it to extract the TEC map data, and output the data in the desired format.

The following code illustrates one way to achieve the same in MATLAB.

clear;clc;
ionexFilePath = 'c2.txt';
fileContents = fileread(ionexFilePath);

% Extract TEC map sections between 'START OF TEC MAP' and 'END OF TEC MAP'
tecMapSections = regexp(fileContents, '(?<=START OF TEC MAP).+?(?=END OF TEC MAP)', 'match');

% Remove the last TEC map section (assumed to be for the next day)
tecMapSections = tecMapSections(1:end-1);

% Initialize a 3D array for TEC values with dimensions based on
% the number of TEC map sections (73x71x24)
tecValuesArray = zeros(73, 71, length(tecMapSections));

% Function to convert latitude to an index in the TEC values array
latitudeToIndex = @(latitude) round((latitude+87.5)/2.5)+1;

for mapIndex = 1 : length(tecMapSections)
    % Split the TEC map section at the first newline character
    sectionBuffer = regexp(tecMapSections{mapIndex}, '\n', 'split', 'once');
    % Split again at the first newline character
    sectionBuffer = regexp(sectionBuffer{2}, '\n', 'split', 'once');
    % Split the string into parts at 'LAT/LON1/LON2/DLON/H'
    tecDataParts = regexp(sectionBuffer{2}, 'LAT/LON1/LON2/DLON/H', 'split');
    % The first part contains the latitude information
    latitudeString = tecDataParts{1};
    
    for dataPartIndex = 2 : length(tecDataParts)
        % Extract the latitude value from the latitude string
        latitudeValue = textscan(latitudeString,'%f%*[^\n]');
        latitudeValue = latitudeValue{1};
        % Read TEC values from the current part, excluding the last 60 characters
        tecValues = sscanf(tecDataParts{dataPartIndex}(1:end-60), '%f');
        % Update the latitude string with the last 60 characters, trimmed
        latitudeString = strtrim(tecDataParts{dataPartIndex}(end-60+1:end));
        % Store the TEC values in the appropriate location in the array
        tecValuesArray(:,latitudeToIndex(latitudeValue),mapIndex) = tecValues;
    end
end

% Calculate the mean TEC values across all TEC maps for each latitude and longitude
meanTECValues = mean(tecValuesArray, 3);

% Write the mean TEC values to an output file with tab-delimited columns
dlmwrite('outfile.txt', meanTECValues, 'delimiter', '\t');

You can refer to the following links for more information on the functions used in the code above.

• regexp - https://www.mathworks.com/help/matlab/ref/regexp.html
• textscan - https://www.mathworks.com/help/matlab/ref/textscan.html
• sscanf - https://www.mathworks.com/help/matlab/ref/sscanf.html
• strtrim - https://www.mathworks.com/help/matlab/ref/strtrim.html
• dlmwrite - https://www.mathworks.com/help/matlab/ref/dlmwrite.html

Hope this helps with your query.

[ahmad Saad]

Hi Paras Gupta

why your output is not similar to the desired outfile.txt given by Rukundo Wellen

Alos how i can plot the result ?