Signal processing

The file $VULCAN/src/filtering.scm and VULCAN/src/window-filters.scm defines some useful signal processing functions. The class <window-filter> defines an API for applying a window filter to a set of readings. The public fields of this class are:

   (window-size  (self <window-filter>))  // size of the window
   (last-readings (self <window-filter>)) // current values in the window

The methods associated with this class are:

   (mstart (self <window-filter>))
   (reset (self <window-filter>))  // throw away readings
   (add (self <window-filter>) reading)
   (output (self <window-filter>)) // calcualte output of the filter

Different filters calculate their output in different ways. One has to create a subclass of <window-filter> in order to specify the particular output function of the filter. For example, the subclass <mean-window-filter> is such that

(define-method output ((self <mean-window-filter>))
    (if (not (null? (last-readings self)))
        (mean (last-readings self))
        (next-method self))
)

  The call next-method invokes the method output associated with the superclass (i.e. <window-filter>) has to be called.