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.