This is simply a faster version of (nndist(X) <= r)
  or (nncross(X,Y,what="dist") <= r).
has.close(X,r) determines, for each point in the pattern X,
  whether or not this point has a neighbour in the same pattern X
  which lies at a distance less than or equal to r.
has.close(X,r,Y) determines, for each point in the pattern X,
  whether or not this point has a neighbour in the other pattern
  Y which lies at a distance less than or equal to r.
The function has.close is generic, with methods for
  "ppp" and "pp3" and a default method.