Low-level functions to count the number of close pairs of points.
closepaircounts(X, r)crosspaircounts(X, Y, r)
Point patterns (objects of class "ppp").
Maximum distance between pairs of points to be counted as close pairs.
An integer vector of length equal to the number of points in X.
The results of these functions may not agree exactly with
the correct answer (as calculated by a human) and may not
be consistent between different computers and different installations
of R. The discrepancies arise in marginal cases where the interpoint
distance is equal to, or very close to, the threshold rmax.
Floating-point numbers in a computer
are not mathematical Real Numbers: they are approximations using
finite-precision binary arithmetic.
The approximation is accurate to a tolerance of about
.Machine$double.eps.
If the true interpoint distance \(d\) and the threshold rmax
are equal, or if their difference is no more than .Machine$double.eps,
the result may be incorrect.
These are the efficient low-level functions used by spatstat to count close pairs of points in a point pattern or between two point patterns.
closepaircounts(X,r) counts the number of neighbours for
each point in the pattern X. That is, for each point
X[i], it counts the number of other points X[j]
with j != i such that d(X[i],X[j]) <= r where
d denotes Euclidean distance. The result is an integer vector
v such that v[i] is the number of neighbours of
X[i].
crosspaircounts(X,Y,r) counts, for each point
in the pattern X, the number of neighbours in the pattern
Y. That is, for each point
X[i], it counts the number of points Y[j]
such that d(X[i],X[j]) <= r. The result is an integer vector
v such that v[i] is the number of neighbours of
X[i] in the pattern Y.
closepairs to identify all close pairs of points.
# NOT RUN {
a <- closepaircounts(cells, 0.1)
sum(a)
Y <- split(amacrine)
b <- crosspaircounts(Y$on, Y$off, 0.1)
# }
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