decode base64 and unpack binary data.

Hi, I have an XML file which contains packed data in base64 format. I was able to decode it and unpack it using python, but now I need to write a function in matlab to perform this. I was able to decode the base64 data into a vector of class uint8; this vector contains several elements, each element represents 1 byte (number below 255). I have to unpack this vector of data to get the right decimal numbers/ the real data. Each real data number represents 4 elements in my vector (each number is 4 bytes), because the unpacked data should be floats. Attached my code, please look at the end of it when I tried using fread.

clc
clear all
close all

file = 'C:\Users\Iris\Desktop\cam5-20140227T061344Z.xml';

fid = fopen(file);
if fid == -1
    disp('file open not succesful')
else

      while feof(fid) == 0
          line = fgetl(fid);
          if isempty(strfind(line,'data')) == 0
              rawdata = line;
              rawdata = rawdata(1:length(rawdata)-7);   % This line NEEDS to 
              %be tested with other files. If it doesn't work a string find 
              %'</data>' can be used.
          end
      end

end
closeresult = fclose(fid);    
if closeresult == 0
    disp('file close succesful')
else
    disp('file did not close correctly')
end

packed_data = base64decode(rawdata);  %these are decimals
save('rawdata.mat','packed_data');

fid = fopen('rawdata.mat');
data = fread(fid,length(packed_data),'uint8=>float','b');
closed = fclose(fid);
if closed == 0;
    disp('file closed')
else
    fisp('file not close')
end

Answer 1

[Jan]

The indirection of using a file is always a bad idea. What about this:

packed_data = base64decode(rawdata);
float_data  = typecast(packed_data, 'single');

But if you really want to udes fread, try 'float=>float' instead of 'uint8=>float'