Hi R users,
This query is regarding the use of the 'envelope' function in Spatstat.
My data can be represented as a point process with CONTINUOUS marks:
points <- ppp(x=x,y=y, marks=m, window= wind)
However the marks are alignments (lines), and so have to be treated
differently to normal scalar marks. Hence to create a mcf object with the
appropriate test function for alignment marks, I input 'func' (below)
suggested by Stoyan & Penttinen (1989):
func <- function(m1,m2) { sin(abs(m1-m2))^2}
mcf <- markcorr(points, func, normalise = TRUE, method="density")
So far, so good. However, usinf 'envelope' and 'rlabel' I would like to
check if the pattern in the data is lost when randomly relabeling the mark
for each point. If the test function, 'func' were the usual G(m1,m2)=m1*m2,
then the following would work:
E <- envelope(points, markcorr, nsim=20,
simulate=expression(rlabel(points)))
Howeve, in the above 'markcorr' calculates G(m1,m2)=m1*m2 by default. So
need to specify the test function to be G(m1,m2)= sin(abs(m1-m2))^2.
According to the spatstat manual (p177), I may need to 'cook up' a specific
function, like this:
Kdif = function(X, ..., i) {
Kidot = Kdot(X, ..., i = i)
K = Kest(X, ...)
dif = eval.fv(Kidot - K)
return(dif)
}
E = envelope(lansing, Kdif, i='blackoak',
simulate=expression(rlabel(lansing)))
So how do I tell 'envelope' that I want to specify the mark correlation
test function ??
Many thanks in advance!
T
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