The function fardist is generic, with methods for
  the classes owin and ppp.
For a window W, the command fardist(W)
  returns a pixel image in which the value at each pixel
  is the largest distance from that pixel to the boundary of
  W.
For a point pattern X, with window W, the
  command fardist(X) returns a numeric vector
  with one entry for each point of X, giving the
  largest distance from that data point to the boundary of W.