These are the summary methods
  for the classes "funxy" and "distfun".
  
An object of class "funxy" represents a function
  of spatial location, defined in a particular region of space.
  This includes objects of the special class "distfun" which represent
  distance functions.
The summary method computes a summary of the function values.
  The function is evaluated on a grid of locations using
  as.im and numerical values at these locations
  are summarised using summary.im. The pixel resolution
  for the grid of locations is determined by the arguments
  ... which are passed to as.mask.