Smooth

This functionality allows a user to smooth the current view in the
plot window. The data will remain visible, but a smoothed line will be
drawn overlaid on the data.  (If "Show Points" is turned off using
the Options menu, the smoothed line can appear even when the points
do not.)

Various controls are used. A menu of smoother types, which at present
contain only two simple smoothers: mean and median of a running
window. The smoothing window size and the amount of the step are set
by two scrollbars.

Smoothing is done in a regression sense, on vertical with the window
based on horizontal distance, at the world data level. Differently
colored points are separately smoothed, that is, each color is treated
as a group.

Plot1D - variable values are smoothed in windows on the texturing
  variable (if dotplotting), or on the density plot (if using average
  shifted histograms).

XYPlot - Y values are smoothed in windows based on X distance.

Rotate, Tour, Corr - current projection is smoothed.

NOTE, the smoothed lines are somewhat transient.  Changing plot modes
or exposing or resizing the XGobi window will erase the lines.