Creating an annotation file

In this example, we will create an annotation file that annotates the first two P-waves of record 100s. These are located at (roughly) sample numbers 315 and 610. First, let's find the annotation code for a P-wave:

    >> WFDB_strann('p')
    ans =
        24

The description is:

    >> WFDB_anndesc(24)
    ans =
    P-wave peak

Create the two annotations:

    >> ANN = WFDB_Annotation(2)
    ANN = 
    1x2 struct array with fields:
        time
        anntyp
        subtyp
        chan
        num
        aux
    >> ANN(1).time = 315;
    >> ANN(1).anntyp = 24;
    >> ANN(1).aux = 'First P-wave';
    >> ANN(2).time = 610;
    >> ANN(2).anntyp = 24;
    >> ANN(2).aux = 'Second P-wave';

Now create an annotator structure:

    >> A = WFDB_Anninfo(1)
    A = 
        name: 'a1'
        stat: 'WFDB_READ'
    >> A.name = 'p';
    >> A.stat = 'WFDB_WRITE';

Create an empty annotation file to hold the annotations:

    >> WFDB_annopen('100s', A)

Write the annotations:

    >> WFDB_putann(0, ANN)

The first argument of WFDB_putann is the output annotator number. Since we are writing only one annotation file, its annotator number is 0.

Close all open files:

    >> WFDB_wfdbquit

The new annotation file, 100s.p, will be located in MATLAB's current directory. The result may be verified using WAVE (under Linux) or GTKWave (under MS-Windows). These interactive viewers can be called from MATLAB using:

    >> !wave -r 100s -a p &

(substitute gtkwave for wave under MS-Windows).

(Remember the !-sign to call system functions from MATLAB and the &-sign to run WAVE as a background process; depending on your setup, using & may cause an error, however, and you may need to run WAVE as a foreground process without the final '&' in the command.)

An elaborated version of this example is provided in the examples directory of the WFDB_tools package (look for example3.m).