Find Peaks Dialog

This dialog box is opened when you select the Peaks... command from the Analysis menu. By pressing the Find button QtiPlot performs a search on the selected curve using the first derivative method. This method is based on the fact that the first derivative of a function at a local extreme point is equal to zero. The limits of the search range can be specified via the From Xmin and To Xmax input boxes.

Figure 5-105. The Find Peaks dialog box.

The Direction drop-down list can be used in order to specify which type of peaks should be detected: only Positive peaks, only Negative peaks or Both positive and negative peaks.

The Filter Height can be used to specify the minimum height of the found peaks. It is defined as follows: if it is set to zero the standard deviation of the data is used as a threshold height else it is a percent of the maximum value of the dataset.

It is possible to specify the method to smooth the derivative of the spectrum data. The available methods are:

  1. None: Do not use any smoothing method.

  2. Savitsky-Golay: Specifies the Savitsky-Golay method to get smooth the derivative.

  3. FFT: Specifies the FFT Filter method to smooth the derivative.

  4. Moving Window Average: Specifies the Moving Window Average method to smooth the derivative.

In the Display group select the Center check box to mark the center of the peaks. The line style of the plotted peaks can also be specified.

Select the Labels check box to display labels on the data plot for each peak found. It is possible to select the type of center labels:

  1. X: Use the X coordinates of the peak centers as center labels.

  2. Y: Use the Y coordinates of the peak centers as center labels.

  3. Row Indices: Use the indices of the peaks as center labels.

  4. (X,Y): Use the X and Y coordinates of the peak centers as labels.

Use the Rotate -90 check box to specify whether or not to rotate the center labels.