Computes simulation envelopes of a summary function for a three-dimensional point pattern.
# S3 method for pp3
envelope(Y, fun=K3est, nsim=99, nrank=1, …,
funargs=list(), funYargs=funargs, simulate=NULL, verbose=TRUE,
transform=NULL,global=FALSE,ginterval=NULL,use.theory=NULL,
alternative=c("two.sided", "less", "greater"),
scale=NULL, clamp=FALSE,
savefuns=FALSE, savepatterns=FALSE,
nsim2=nsim, VARIANCE=FALSE, nSD=2, Yname=NULL, maxnerr=nsim,
do.pwrong=FALSE, envir.simul=NULL)A three-dimensional point pattern (object of class
"pp3").
Function that computes the desired summary statistic for a 3D point pattern.
Number of simulated point patterns to be generated when computing the envelopes.
Integer. Rank of the envelope value amongst the nsim simulated
values. A rank of 1 means that the minimum and maximum
simulated values will be used.
Extra arguments passed to fun.
A list, containing extra arguments to be passed to fun.
Optional. A list, containing extra arguments to be passed to
fun when applied to the original data Y only.
Optional. Specifies how to generate the simulated point patterns.
If simulate is an expression in the R language, then this
expression will be evaluated nsim times,
to obtain nsim point patterns which are taken as the
simulated patterns from which the envelopes are computed.
If simulate is a list of point patterns, then the entries
in this list will be treated as the simulated patterns from which
the envelopes are computed.
Alternatively simulate may be an object produced by the
envelope command: see Details.
Logical flag indicating whether to print progress reports during the simulations.
Optional. A transformation to be applied to the function values, before the envelopes are computed. An expression object (see Details).
Logical flag indicating whether envelopes should be pointwise
(global=FALSE) or simultaneous (global=TRUE).
Optional.
A vector of length 2 specifying
the interval of \(r\) values for the simultaneous critical
envelopes. Only relevant if global=TRUE.
Logical value indicating whether to use the theoretical value,
computed by fun, as the reference value for simultaneous
envelopes. Applicable only when global=TRUE.
Character string determining whether the envelope corresponds
to a two-sided test (side="two.sided", the default)
or a one-sided test with a lower critical boundary
(side="less") or a one-sided test
with an upper critical boundary (side="greater").
Optional. Scaling function for global envelopes.
A function in the R language which determines the
relative scale of deviations, as a function of
distance \(r\), when computing the global envelopes.
Applicable only when global=TRUE.
Summary function values for distance r
will be divided by scale(r) before the
maximum deviation is computed. The resulting global envelopes
will have width proportional to scale(r).
Logical value indicating how to compute envelopes when
alternative="less" or alternative="greater".
Deviations of the observed
summary function from the theoretical summary function are initially
evaluated as signed real numbers, with large positive values indicating
consistency with the alternative hypothesis.
If clamp=FALSE (the default), these values are not changed.
If clamp=TRUE, any negative values are replaced by zero.
Logical flag indicating whether to save all the simulated function values.
Logical flag indicating whether to save all the simulated point patterns.
Number of extra simulated point patterns to be generated
if it is necessary to use simulation to estimate the theoretical
mean of the summary function. Only relevant when global=TRUE
and the simulations are not based on CSR.
Logical. If TRUE, critical envelopes will be calculated
as sample mean plus or minus nSD times sample standard
deviation.
Number of estimated standard deviations used to determine
the critical envelopes, if VARIANCE=TRUE.
Character string that should be used as the name of the
data point pattern Y when printing or plotting the results.
Maximum number of rejected patterns.
If fun yields an error when applied to a simulated point
pattern (for example, because the pattern is empty and fun
requires at least one point), the pattern will be rejected
and a new random point pattern will be generated. If this happens
more than maxnerr times, the algorithm will give up.
Logical. If TRUE, the algorithm will also estimate
the true significance level of the “wrong” test (the test that
declares the summary function for the data to be significant
if it lies outside the pointwise critical boundary at any
point). This estimate is printed when the result is printed.
Environment in which to evaluate the expression simulate,
if not the current environment.
A function value table (object of class "fv")
which can be plotted directly.
See envelope for further details.
The envelope command performs simulations and
computes envelopes of a summary statistic based on the simulations.
The result is an object that can be plotted to display the envelopes.
The envelopes can be used to assess the goodness-of-fit of
a point process model to point pattern data.
The envelope function is generic, with methods for
the classes "ppp", "ppm" and "kppm"
described in the help file for envelope.
This function envelope.pp3 is the method for
three-dimensional point patterns (objects of class "pp3").
For the most basic use, if you have a 3D point pattern X and
you want to test Complete Spatial Randomness (CSR), type
plot(envelope(X, K3est,nsim=39)) to see the three-dimensional
\(K\) function for X plotted together with the envelopes of
the three-dimensional \(K\) function for 39 simulations of CSR.
To create simulation envelopes, the command envelope(Y, ...)
first generates nsim random point patterns
in one of the following ways.
If simulate=NULL,
then we generate nsim simulations of
Complete Spatial Randomness (i.e. nsim simulated point patterns
each being a realisation of the uniform Poisson point process)
with the same intensity as the pattern Y.
If simulate is supplied, then it determines how the
simulated point patterns are generated.
See envelope for details.
The summary statistic fun is applied to each of these simulated
patterns. Typically fun is one of the functions
K3est, G3est, F3est or pcf3est.
It may also be a character string
containing the name of one of these functions.
For further information, see the documentation for
envelope.
Baddeley, A.J, Moyeed, R.A., Howard, C.V. and Boyde, A. (1993) Analysis of a three-dimensional point pattern with replication. Applied Statistics 42, 641--668.
# NOT RUN {
X <- rpoispp3(20, box3())
# }
# NOT RUN {
plot(envelope(X, nsim=39))
# }
# NOT RUN {
# }
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