Creating the header

We have just now a file with a set of values. To create an EDF+ file, the first thing to do is creating the header. Here we have to take some decisions. As an example we decide that the data record duration will equal one second. So, we will have 5 data records. We will create a continuous EDF+ file but we are going to use methods that can be very easily generalized for discontinuous records.

The header of an EDF+ file is a set of fixed-length ASCII characters. We choose to store the result in a String. Although Strings in Java are formed by 16-bit characters, they can be easily converted to ASCII format. The procedure is highly repetitive and can be followed easily by reading the code.

We define a class called Support where different functions are going to be stored. Let's see its content

class Support{
    public String createHeader(){

	// creates a string with spaces
	String spaces ="";
	for(int i=0; i<80; i++){
	    spaces += " ";
	}

	String str1="";
	String result="";
	int numSignals = 2;

	// VERSION
	str1 = "0"+spaces;
	result += str1.substring(0,8);

	// PATIENT
	str1 = "X X X X"+spaces;
	result += str1.substring(0,80);

	// RECORDING
	str1 = "Startdate 01-JAN-2003 X X X"+spaces;
	result += str1.substring(0,80);

	// STARTDATE
	str1 = "01.01.03"+spaces;
	result += str1.substring(0,8);

	// STARTTIME
	str1 = "10.00.00"+spaces;
	result += str1.substring(0,8);

	// HEADERSIZE
	int bytes_header = (numSignals+1)*256;
	str1 = bytes_header+spaces;
	result += str1.substring(0,8);

	// RESERVED
	str1 = "EDF+C"+spaces;
	result += str1.substring(0,44);
	
	// DATARECORDS
	int n_datarecords = 5;
	str1 = n_datarecords + spaces;
	result +=  str1.substring(0,8);

	// DURATION
	str1 = "1"+spaces;
	result += str1.substring(0,8);

	// SIGNALS
	str1 = numSignals+spaces;
	result += str1.substring(0,4);

	String[] signals = {"Sin wave","EDF Annotations"};
	for (int i=0 ; i< numSignals; i++){
	    str1 = signals[i]+spaces;
	    result += str1.substring(0,16);
	}

	String[] transducers = {"",""} ;
	for (int i=0 ; i< numSignals; i++){
	    str1 = transducers[i]+spaces;
	    result += str1.substring(0,80);
	}

	String[] dimension = {"uV",""};
	for (int i=0 ; i< numSignals; i++){
	    str1 = dimension[i]+spaces;
	    result += str1.substring(0,8);
	}

	String[] physmin = {"-100","0"};
	for (int i=0 ; i< numSignals; i++){
	    str1 = physmin[i]+spaces;
	    result += str1.substring(0,8);
	}

	String[] physmax = {"100","1"};
	for (int i=0 ; i< numSignals; i++){
	    str1 = physmax[i]+spaces;
	    result += str1.substring(0,8);
	}

	String[] digmin = {"-100","-32768"};
	for (int i=0 ; i< numSignals; i++){
	    str1 = digmin[i]+spaces;
	    result += str1.substring(0,8);
	}

	String[] digmax = {"100","32767"};
	for (int i=0 ; i< numSignals; i++){
	    str1 = digmax[i]+spaces;
	    result += str1.substring(0,8);
	}

	String[] prefiltering = {"",""};
	for (int i=0 ; i< numSignals; i++){
	    str1 = prefiltering[i]+spaces;
	    result += str1.substring(0,80);
	}

	int[] nsamples = {100, 50};
	int bytesPerRecord = 0;
	for(int i=0; i<nsamples.length; i++){
	    bytesPerRecord += nsamples[i];
	}
	for (int i=0 ; i< numSignals; i++){
	    str1 = nsamples[i]+spaces;
	    result += str1.substring(0,8);
	}

	String[] reserved = {"",""};
	for (int i=0 ; i< numSignals; i++){
	    str1 = reserved[i]+spaces;
	    result += str1.substring(0,32);
	}

	return result;

    }

}

This is a very repetitive code. Basically, we create a String (result) and we add the different fields. Each field is adjusted to the specification of EDF by adding spaces. We defined two signals: an ordinary signal containing the values and an annotation signal whose label is EDF Annotations. Having at least an annotation signal is a must in EDF+.

Now we need a program to check the function. We create the program SupportTest.java. This is the content

 
public class SupportTest{
    public static void main(String[] args){
	Support mySupport = new Support();
	System.out.println(mySupport.createHeader());
    }
}

We can check the result

[j@localhost Code]$ javac SupportTest.java
[j@localhost Code]$ java SupportTest > test1.edf
[j@localhost Code]$

Now we have an EDF+ file (test1.edf) that contains no data. The file contains only the header.