MATLAB Programming

7 Working with Scientific Data Formats
data 24x5 14784 cell
data_combined 1x5 2364 cell
var_time 24x1 4608 cell
Representing CDF Time Values
CDF represents time differently than MATLAB. CDF represents date and
time as the number of milliseconds since 1-Jan-0000. This is called an epoch
in CDF terminology. MATLAB represents date and time as a serial date
number, which is the number of days since 0-Jan-0000. To represent CDF
dates, MATLAB uses an object called a CDF epoch object. To access the time
information in a CDF object, use the object’s todatenum method.
For example, this code extracts the date information from a CDF epoch object:
1 Extract the date information from the CDF epoch object returned in the
cell array data (see “Importing Data from a CDF File” on page 7-3). Use
the todatenum method of the CDF epoch object to get the date information,
which is returned as a MATLAB serial date number.
m_date = todatenum(data{1});
2 View the MATLAB serial date number as a string.
datestr(m_date)
ans =
01-Jan-2001
Exporting Data to a CDF File
To export data from the MATLAB workspace to a CDF file, use the cdfwrite
function. Using this function, you can write variables and attributes to the
file, specifying their names and associated values. See the cdfwrite reference
page for more information.
ThisexampleshowshowtowritedateinformationtoaCDFfile. Notehow
the example uses the CDF epoch object constructor, cdfepoch, toconverta
MATLAB serial date number into a CDF epoch.
cdfwrite('myfile',{'Time_val',cdfepoch(now)});
7-6