Convert user coordinates to figure region coordinates and conversely.
toFig(x, y = NULL) toUser(x, y = NULL)
| x | the x coordinates of a set of points. Alternatively, a
single argument   | 
    
|---|---|
| y | the y coordinates of a set of points.  | 
    
These functions can be used anytime, however, there are useful only once plot.new has been called.
toFig: Convert figure region coordinates into user coordinates.
toUser: Convert user coordinates into figure region coordinates.