# Kmark

##### Mark-Weighted K Function

Estimates the mark-weighted \(K\) function of a marked point pattern.

- Keywords
- spatial, nonparametric

##### Usage

```
Kmark(X, f = NULL, r = NULL,
correction = c("isotropic", "Ripley", "translate"), ...,
f1 = NULL, normalise = TRUE, returnL = FALSE, fargs = NULL)
``` markcorrint(X, f = NULL, r = NULL,
correction = c("isotropic", "Ripley", "translate"), ...,
f1 = NULL, normalise = TRUE, returnL = FALSE, fargs = NULL)

##### Arguments

- X
The observed point pattern. An object of class

`"ppp"`

or something acceptable to`as.ppp`

.- f
Optional. Test function \(f\) used in the definition of the mark correlation function. An R function with at least two arguments. There is a sensible default.

- r
Optional. Numeric vector. The values of the argument \(r\) at which the mark correlation function \(k_f(r)\) should be evaluated. There is a sensible default.

- correction
A character vector containing any selection of the options

`"isotropic"`

,`"Ripley"`

or`"translate"`

. It specifies the edge correction(s) to be applied. Alternatively`correction="all"`

selects all options.- …
Ignored.

- f1
An alternative to

`f`

. If this argument is given, then \(f\) is assumed to take the form \(f(u,v)=f_1(u)f_1(v)\).- normalise
If

`normalise=FALSE`

, compute only the numerator of the expression for the mark correlation.- returnL
Compute the analogue of the K-function if

`returnL=FALSE`

or the analogue of the L-function if`returnL=TRUE`

.- fargs
Optional. A list of extra arguments to be passed to the function

`f`

or`f1`

.

##### Details

The functions `Kmark`

and `markcorrint`

are identical.
(Eventually `markcorrint`

will be deprecated.)

The *mark-weighted \(K\) function* \(K_f(r)\)
of a marked point process (Penttinen et al, 1992)
is a generalisation of Ripley's \(K\) function, in which the contribution
from each pair of points is weighted by a function of their marks.
If the marks of the two points are \(m_1, m_2\) then
the weight is proportional to \(f(m_1, m_2)\) where
\(f\) is a specified *test function*.

The mark-weighted \(K\) function is defined so that
$$
\lambda K_f(r) = \frac{C_f(r)}{E[ f(M_1, M_2) ]}
$$
where
$$
C_f(r) =
E \left[
\sum_{x \in X}
f(m(u), m(x))
1{0 < ||u - x|| \le r}
\; \big| \;
u \in X
\right]
$$
for any spatial location \(u\) taken to be a typical point of
the point process \(X\). Here \(||u-x||\) is the
euclidean distance between \(u\) and \(x\), so that the sum
is taken over all random points \(x\) that lie within a distance
\(r\) of the point \(u\). The function \(C_f(r)\) is
the *unnormalised* mark-weighted \(K\) function.
To obtain \(K_f(r)\) we standardise \(C_f(r)\)
by dividing by \(E[f(M_1,M_2)]\), the expected value of
\(f(M_1,M_2)\) when \(M_1\) and \(M_2\) are
independent random marks with the same distribution as the marks in
the point process.

Under the hypothesis of random labelling, the mark-weighted \(K\) function is equal to Ripley's \(K\) function, \(K_f(r) = K(r)\).

The mark-weighted \(K\) function is sometimes called the
*mark correlation integral* because it is related to the
mark correlation function \(k_f(r)\)
and the pair correlation function \(g(r)\) by
$$
K_f(r) = 2 \pi \int_0^r s k_f(s) \, g(s) \, {\rm d}s
$$
See `markcorr`

for a definition of the
mark correlation function.

Given a marked point pattern `X`

,
this command computes edge-corrected estimates
of the mark-weighted \(K\) function.
If `returnL=FALSE`

then the estimated
function \(K_f(r)\) is returned;
otherwise the function
$$
L_f(r) = \sqrt{K_f(r)/\pi}
$$
is returned.

##### Value

An object of class `"fv"`

(see `fv.object`

).

Essentially a data frame containing numeric columns

the values of the argument \(r\) at which the mark correlation integral \(K_f(r)\) has been estimated

the theoretical value of \(K_f(r)\) when the marks attached to different points are independent, namely \(\pi r^2\)

##### References

Penttinen, A., Stoyan, D. and Henttonen, H. M. (1992)
Marked point processes in forest statistics.
*Forest Science* **38** (1992) 806-824.

Illian, J., Penttinen, A., Stoyan, H. and Stoyan, D. (2008)
*Statistical analysis and modelling of spatial point patterns*.
Chichester: John Wiley.

##### See Also

`markcorr`

to estimate the mark correlation function.

##### Examples

```
# NOT RUN {
# CONTINUOUS-VALUED MARKS:
# (1) Spruces
# marks represent tree diameter
# mark correlation function
ms <- Kmark(spruces)
plot(ms)
# (2) simulated data with independent marks
X <- rpoispp(100)
X <- X %mark% runif(npoints(X))
Xc <- Kmark(X)
plot(Xc)
# MULTITYPE DATA:
# Hughes' amacrine data
# Cells marked as 'on'/'off'
M <- Kmark(amacrine, function(m1,m2) {m1==m2},
correction="translate")
plot(M)
# }
```

*Documentation reproduced from package spatstat, version 1.55-1, License: GPL (>= 2)*