RV Cross Correlation
 
    c    	Select (cut) a region to be used in the correlation.  
    d    	Print the difference in pixels between two points on a spectrum.
    g    	Select the region of the correlation plot to be fit.
    l    	Page the current logfile of results if a logfile is being kept.
    p           Plot the data points as markers to the screen (corr. plot only).
    q    	Quit the task.
    r    	Replot the data.
    s    	Shift the object spectrum.  
    x    	Do the cross correlation.
    y           Same as 'g' but uses Y position to get endpoints.
    z           Zoom in on cursor X position.
    ?    	Print a help summary of keystrokes and commands.
 
The following colon commands may be used to set or show a named task parameter.
To show the current value of the parameter, just type it's name following a ':'.
 
    :apodize   [real_value]		  # Percentage of ends to be apodized
    :batch     [rewind]			  # Continue processing of the input 
					  # list with the current parameters
    :corrfunc  [difference|fourier] 	  # correlation method used.
    :cutoff    [int_value]		  # Set/show the cutoff wavenumber 
    :cuton     [int_value]		  # Set/show the cutoff wavenumber 
    :filter    [yes|no]			  # Set/show the filter flag
    :fitfunc   [gaussian|parabola]        # function fit to correlation plot.
    :fulloff   [int_value]		  # Set/show the cutoff wavenumber 
    :fullon    [int_value]		  # Set/show the cutoff wavenumber 
    :initshift [int_value] 		  # initial shift value.
    :maxshift  [int_value] 		  # maximum shift value.
    :maxpeak   [int_value] 		  # max shift value of expected peak
    :next[!]    			  # Read in the next object spectrum in
				          # the input list.
    :objects   [list] 	    	  	  # object image name. 
    :previous[!]			  # Read in the previous object spectrum
    					  # in the input list.
    :refspec   [file] 		  	  # reference image name.
    :regions   [range] 		  	  # regions used in the correlation.
    :show       			  # List the current values of all the 
					  # parameters.
    :specplot  [yes|no]			  # Set/show spec_plot flag
    :unlearn				  # Reset parameters to the defaults
    :update      			  # Update the parameter file with the 
    :write[!]  				  # Write the results of the correlation
				          # to the logfile and the header
				          # current parameter values