khat {splancs} | R Documentation |
Calculates an estimate of the K-function
khat(pts,poly,s,newstyle=FALSE) print.khat(x, ...) plot.khat(x, ...)
pts |
A points data set |
poly |
A polygon containing the points |
s |
A vector of distances at which to calculate the K function |
newstyle |
if TRUE, the function returns a khat object |
x |
a khat object |
... |
other arguments passed to plot and print functions |
The K function is defined as the expected number of further points within a distance s of an arbitrary point, divided by the overall density of the points. In practice an edge-correction is required to avoid biasing the estimation due to non-recording of points outside the polygon.
The newstyle argument and khat object were introduced in collaboration with Thomas de Cornulier <oedic@cebc.cnrs.fr> to permit the mapping of counts or khats for chosen distance values, as in ftp://pbil.univ-lyon1.fr/pub/mac/ADE/ADE4/DocThemPDFUS/Thema81.pdf, p.18.
If newstyle
is FALSE,
a vector like s
containing the value of K at the points in s
.
else a khat
object list with:
khat |
the value of K at the points in s |
counts |
integer matrix of counts of points within the vector of
distances s for each point |
khats |
matrix of values of K within the vector of distances s
for each point |
s |
s |
Ripley, B.D. 1976 The second-order analysis of stationary point processes, J. Appl. Prob, 13 255-266; Rowlingson, B. and Diggle, P. 1993 Splancs: spatial point pattern analysis code in S-Plus. Computers and Geosciences, 19, 627-655; the original sources can be accessed at: http://www.maths.lancs.ac.uk/~rowlings/Splancs/. See also Bivand, R. and Gebhardt, A. 2000 Implementing functions for spatial statistical analysis using the R language. Journal of Geographical Systems, 2, 307-317.
data(cardiff) s <- seq(2,30,2) plot(s, sqrt(khat(as.points(cardiff), cardiff$poly, s)/pi) - s, type="l", xlab="Splancs - polygon boundary", ylab="Estimated L", ylim=c(-1,1.5)) newstyle <- khat(as.points(cardiff), cardiff$poly, s, newstyle=TRUE) str(newstyle) newstyle apply(newstyle$khats, 2, sum) plot(newstyle)