Compute Expansion Window for Simulation
Defines the default expansion window for simulation of a fitted point process model.
default.expand(object, m=2, epsilon=1e-6)
- A fitted point process model (object of class
- A single numeric value.
The window will be expanded by a distance
m * reach(object)along each side.
- Threshold argument passed to
This function computes a default value for the
expansion window (the argument
given a fitted point process model
This default is used by
qqplot.ppm and other functions.
Suppose we wish to generate simulated realisations
of a fitted point process model inside a window
It is advisable to first simulate
the pattern on a larger window, and then clip it to the original
w. This avoids edge effects in the simulation.
It is called expansion of the simulation window.
Accordingly, for the Metropolis-Hastings simulation algorithm
rmh, the algorithm control parameters specified by
rmhcontrol include an argument
determines the expansion of the simulation window.
default.expand determines the default expansion
window for a fitted point process model
If the model depends on external covariates (i.e. covariates other than
the Cartesian covariates
y and the
then no expansion is performed, and
default.expand returns the
w = as.owin(object).
Otherwise, the original window
w = as.owin(object) is expanded by
m * rr, where
rr is the interaction range of the model, computed by
w is a rectangle then
each edge of
w is displaced outward by distance
m * rr.
w is not a rectangle then
w is dilated by
m * rr using
- A window (object of class
data(cells) fit <- ppm(cells, ~1, Strauss(0.07)) default.expand(fit)