nncross {spatstat} | R Documentation |
Given two point patterns X
and Y
,
finds the nearest neighbour in Y
of each point of X
.
Alternatively Y
may be a line segment pattern.
nncross(X, Y, iX=NULL, iY=NULL)
X |
Point pattern (object of class |
Y |
Either a point pattern (object of class |
iX, iY |
Optional identifiers, applicable only in the case where
|
Given two point patterns X
and Y
this
function finds, for each point of X
,
the nearest point of Y
. The distance between these points
is also computed.
Alternatively if X
is a point pattern and Y
is a line
segment pattern, the function finds the nearest line segment to each point
of X
, and computes the distance.
The return value is a data frame, with rows corresponding to
the points of X
. The first column gives the nearest neighbour
distances (i.e. the i
th entry is the distance
from the i
th point of X
to the nearest element of
Y
). The second column gives the indices of the nearest
neighbours (i.e.\ the i
th entry is the index of
the nearest element in Y
.)
Note that this function is not symmetric in X
and Y
.
To find the nearest neighbour in X
of each point in Y
,
where Y
is a point pattern, use nncross(Y,X)
.
The arguments iX
and iY
are used when
the two point patterns X
and Y
have some points in
common. In this situation nncross(X, Y)
would return some zero
distances. To avoid this, attach a unique integer identifier to
each point, such that two points are identical if their
identifying numbers are equal. Let iX
be the vector of
identifier values for the points in X
, and iY
the vector of identifiers for points in Y
. Then the code
will only compare two points if they have different values of the
identifier. See the Examples.
A data frame with two columns:
dist |
Nearest neighbour distance |
which |
Nearest neighbour index in |
Adrian Baddeley Adrian.Baddeley@csiro.au http://www.maths.uwa.edu.au/~adrian/ and Rolf Turner r.turner@auckland.ac.nz
nndist
for nearest neighbour
distances in a single point pattern.
# two different point patterns X <- runifpoint(15) Y <- runifpoint(20) N <- nncross(X,Y)$which # note that length(N) = 15 plot(superimpose(X=X,Y=Y), main="nncross", cols=c("red","blue")) arrows(X$x, X$y, Y[N]$x, Y[N]$y, length=0.15) # two patterns with some points in common Z <- runifpoint(50) X <- Z[1:30] Y <- Z[20:50] iX <- 1:30 iY <- 20:50 N <- nncross(X,Y, iX, iY)$which plot(superimpose(X=X, Y=Y), main="nncross", cols=c("red","blue")) arrows(X$x, X$y, Y[N]$x, Y[N]$y, length=0.15) # point pattern and line segment pattern X <- runifpoint(15) Y <- rpoisline(10) N <- nncross(X,Y)