default.expand(object, m=2, epsilon=1e-6)
"ppp"
).m * reach(object)
along each side.reach.ppm
to determine
reach(object)
."owin"
)
or the numeric value 1, representing no expansion.expand
in rmhcontrol
)
given a fitted point process model object
.
This default is used by envelope
,
qqplot.ppm
, simulate.ppm
and other functions. Suppose we wish to generate simulated realisations
of a fitted point process model inside a window w
.
It is advisable to first simulate
the pattern on a larger window, and then clip it to the original
window 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 expand
that
determines the expansion of the simulation window.
The function default.expand
determines the default expansion
window for a fitted point process model object
.
If the model is Poisson, then no expansion is necessary.
No expansion is performed by default,
and default.expand
returns the value 1, representing no expansion.
The simulation window is the original window w = as.owin(object)
.
If the model depends on external covariates (i.e. covariates other than
the Cartesian covariates x
and y
and the marks
)
then no expansion is feasible, in general, because the spatial domain
of the covariates is not guaranteed to be large enough.
default.expand
returns the value 1, representing no expansion.
The simulation window is the original window w = as.owin(object)
.
If the model depends on the Cartesian covariates x
and y
,
it would be feasible to expand the simulation window, and this was the
default for x
or y
.
Again default.expand
returns the value 1, representing no expansion.
Otherwise, expansion will occur.
The original window w = as.owin(object)
is expanded by
a distance m * rr
, where
rr
is the interaction range of the model, computed by
reach
. If w
is a rectangle then
each edge of w
is displaced outward by distance m * rr
.
If w
is not a rectangle then w
is dilated by
distance m * rr
using dilation
.
rmhcontrol
,
rmh
,
envelope
,
qqplot.ppm
data(cells)
fit <- ppm(cells, ~1, Strauss(0.07))
default.expand(fit)
Run the code above in your browser using DataLab