Multitype pair correlation function (i-to-any)
Calculates an estimate of the multitype pair correlation function
(from points of type i to points of any type)
for a multitype point pattern.
pcfdot(X, i, ..., r = NULL,
kernel = "epanechnikov", bw = NULL, stoyan = 0.15,
correction = c("isotropic", "Ripley", "translate"),
divisor = c("r", "d"))X |
The observed point pattern, from which an estimate of the dot-type pair correlation function gdot[i](r) will be computed. It must be a multitype point pattern (a marked point pattern whose marks are a factor). |
i |
The type (mark value)
of the points in |
... |
Ignored. |
r |
Vector of values for the argument r at which g(r) should be evaluated. There is a sensible default. |
kernel |
Choice of smoothing kernel,
passed to |
bw |
Bandwidth for smoothing kernel,
passed to |
stoyan |
Coefficient for default bandwidth rule; see Details. |
correction |
Choice of edge correction. |
divisor |
Choice of divisor in the estimation formula:
either |
This is a generalisation of the pair correlation function pcf
to multitype point patterns.
For two locations x and y separated by a nonzero distance r, the probability p(r) of finding a point of type i at location x and a point of any type at location y is
p(r) = lambda[i] * lambda * gdot[i](r) dx dy
where lambda is the intensity of all points, and lambda[i] is the intensity of the points of type i. For a completely random Poisson marked point process, p(r) = lambda[i] * lambda so gdot[i](r) = 1.
For a stationary multitype point process, the
type-i-to-any-type pair correlation
function between marks i and j is formally defined as
g(r) = Kdot[i]'(r)/ ( 2 * pi * r)
where Kdot[i]'(r) is the derivative of
the type-i-to-any-type K function
Kdot[i](r).
of the point process. See Kdot for information
about Kdot[i](r).
The command pcfdot computes a kernel estimate of
the multitype pair correlation function from points of type i
to points of any type.
If divisor="r" (the default), then the multitype
counterpart of the standard
kernel estimator (Stoyan and Stoyan, 1994, pages 284–285)
is used. By default, the recommendations of Stoyan and Stoyan (1994)
are followed exactly.
If divisor="d" then a modified estimator is used:
the contribution from
an interpoint distance d[ij] to the
estimate of g(r) is divided by d[ij]
instead of dividing by r. This usually improves the
bias of the estimator when r is close to zero.
There is also a choice of spatial edge corrections
(which are needed to avoid bias due to edge effects
associated with the boundary of the spatial window):
correction="translate" is the Ohser-Stoyan translation
correction, and correction="isotropic" or "Ripley"
is Ripley's isotropic correction.
The choice of smoothing kernel is controlled by the
argument kernel which is passed to density.
The default is the Epanechnikov kernel.
The bandwidth of the smoothing kernel can be controlled by the
argument bw. Its precise interpretation
is explained in the documentation for density.default.
For the Epanechnikov kernel with support [-h,h],
the argument bw is equivalent to h/sqrt(5).
If bw is not specified, the default bandwidth
is determined by Stoyan's rule of thumb (Stoyan and Stoyan, 1994, page
285). That is,
h = c/sqrt(lambda),
where lambda is the (estimated) intensity of the
unmarked point process,
and c is a constant in the range from 0.1 to 0.2.
The argument stoyan determines the value of c.
Essentially a data frame containing columns
r |
the vector of values of the argument r at which the function gdot[i] has been estimated |
theo |
the theoretical value gdot[i](r) = r for independent marks. |
together with columns named
"border", "bord.modif",
"iso" and/or "trans",
according to the selected edge corrections. These columns contain
estimates of the function g[i,j]
obtained by the edge corrections named.
Adrian Baddeley Adrian.Baddeley@curtin.edu.au
and Rolf Turner r.turner@auckland.ac.nz
Mark connection function markconnect.
data(amacrine) p <- pcfdot(amacrine, "on") p <- pcfdot(amacrine, "on", stoyan=0.1) plot(p)
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