Description Usage Arguments Details Value Sorting data and presorted data Warning About Ties Author(s) See Also Examples
Given a point pattern, this function constructs pixel images giving the distance from each pixel to its kth nearest neighbour in the point pattern, and the index of the kth nearest neighbour.
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X 
Point pattern (object of class 
k 
Integer, or integer vector. The algorithm will find the

what 
Character string specifying what information should be returned.
Either the nearest neighbour distance ( 
... 
Arguments passed to 
W 
Window (object of class 
is.sorted.X 
Logical value attesting whether the point pattern 
sortby 
Determines which coordinate to use to sort the point pattern. See Details. 
Given a point pattern X
, this function constructs two pixel images:
a distance map giving, for each pixel,
the distance to the nearest point of X
;
a nearest neighbour map giving, for each pixel,
the identifier of the nearest point of X
.
If the argument k
is specified, then the k
th nearest
neighbours will be found.
If what="dist"
then only the distance map is returned.
If what="which"
then only the nearest neighbour map
is returned.
The argument k
may be an integer or an integer vector.
If it is a single integer, then the k
th nearest neighbours
are computed. If it is a vector, then the k[i]
th nearest
neighbours are computed for each entry k[i]
. For example, setting
k=1:3
will compute the nearest, secondnearest and
thirdnearest neighbours.
A pixel image, or a list of pixel images.
By default (if what=c("dist", "which")
), the result is
a list with two components dist
and which
containing the distance map and the nearest neighbour map.
If what="dist"
then the result is a realvalued pixel image
containing the distance map.
If what="which"
then the result is an integervalued pixel image
containing the nearest neighbour map.
If k
is a vector of several integers, then the result is
similar except that each pixel image is replaced by a list of
pixel images, one for each entry of k
.
Read this section if you care about the speed of computation.
For efficiency, the algorithm sorts the point pattern X
into increasing order of the x coordinate
or increasing order of the the y coordinate.
Sorting is only an intermediate step;
it does not affect the output, which is always given in the same
order as the original data.
By default (if sortby="range"
),
the sorting will occur on the coordinate that has the larger range of
values (according to the frame of the enclosing window of X
).
If sortby = "var"
), sorting will occur on the coordinate that
has the greater variance (in the pattern X
).
Setting sortby="x"
or sortby = "y"
will specify that
sorting should occur on the x or y coordinate, respectively.
If the point pattern X
is already
sorted, then the argument is.sorted.X
should be set to TRUE
, and sortby
should be set
equal to "x"
or "y"
to indicate which coordinate
is sorted.
Ties are possible: there may be two data points
which lie exactly the same distance away from a particular pixel.
This affects the results from nnmap(what="which")
.
The handling of ties is not welldefined: it is not consistent
between different computers and different installations of R.
If there are ties, then different calls to nnmap(what="which")
may give inconsistent results. For example, you may get a different answer
from nnmap(what="which",k=1)
and nnmap(what="which", k=1:2)[[1]]
.
, \rolf , and Jens Oehlschlaegel
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