Start the signal processing dialogue again, this time from the main window using the menu 'Signal Processing-> Create Processed Signal'. Now click on the 'interpolation' button. The interpolation dialogue consists of two columns of three editable text fields, a row of option buttons, and the three clickable buttons. The 'Apply' and 'Exit' buttons will apply the selected interpolation parameters.

In the case of 2 or more existing signals being processed, then a decision has to be made about the positioning of the data points. If the data points coincide in time (which is usually the x-axis for JET signals), then the time points which are used are the existing ones. If the time points do not coincide, then the default is to take a linear interpolation of each signal onto the superset of the time points of the 2 (or more) signals. If a signal does not exist in a certain range, then no interpolation will be possible in that range. This is shown in the diagram below.

To demonstrate the use of interpolation first set up the dialogue as shown below and click on 'Create Signal'.

Before closing this dialogue click on the 'Interpolation...' button. Click on the Start of desired time range text field. Change the value in this field to 45.0. Then click on the End of desired time range text field. Change this value to 55.0.

Now click on the Number of desired time points text field. Change this value to 100. Leave the Interpolation method as 'linear'. Now click 'Apply'. Then click 'Exit'.

The interpolation parameters have now been set. Go to the signal processing dialogue. Click on the 'Create signal' button. You should have now created a new signal called DIFF1. This signal should have been added to the main JETDSP window. Select DIFF2 and DIFF3 and plot it using the 'Plot' menu. DIFF3 should start at 45.0 seconds and end at 55.0 seconds. It should have 100 equally spaced data points in this range. Compare this with the signal DIFF2. Try zooming in on the range 45.0 to 55.0 seconds. The two signals should be very similar except for their range and the spacing of their data points.

The interpolation dialogue sets several important parameters. The time range text fields specify the region of the signal that the user wishes to examine. If they are equal, then the superset of time points is used. The number of data points instructs the interpolation to use exactly this number of points in the interpolation region. Finally, the interpolation method can either be linear or cubic.

The default parameters are to take the superset of time points in the region where all of the signals in the processed signal command exist and to use a linear interpolation.

If the user requries a different interpolation, then they should enter the time range that they wish to examine, choose the number of points that they wish to have in that time range (or leave this set to 0 to use the superset in that range) and then choose their point spacing and interpolation method. Clicking on 'Apply' will set the interpolation parameters, and 'Exit' will dismiss the dialogue.

The user will then be returned to the signal processing dialogue, where they must click 'Create Signal' to actually produce the result.

Note that only equal points spacing is currently available and alternative point spacings will be made available in the future.

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