The argument model represents a fitted spatial point process
model (such as an object of class "ppm", "kppm" or
similar) or a specification of a point process model
(such as an object of class "zclustermodel").
This function returns TRUE if the model is a Poisson cluster
process, and FALSE otherwise.
The function is.poissonclusterprocess is generic, with methods
for classes kppm and zclustermodel, and a default
method.