Construct a space-time planar point pattern from a list
object
Usage
## S3 method for class 'list':
stppp(P, ...)
Arguments
P
list object containing $data, an (n x 3) matrix
corresponding to (x,y,t) values; $tlim, a vector of
length 2 givign the observation time window; and $window
giving an owin spatial observation winow, see ?owin for
more details