The function is.connected is generic. This is the method for
point patterns (objects of class "ppp").
The point pattern X is first converted into an abstract graph
by joining every pair of points that lie closer than R units
apart. Then the algorithm determines whether this graph is connected.
That is, the result of is.connected(X) is TRUE
if any point in X can be reached from any other point,
by a series of steps between points of X,
each step being shorter than R units in length.