Randomly shifts the segments in a line segment pattern.
# S3 method for psp
rshift(X, …, group=NULL, which=NULL)Line segment pattern to be subjected to a random shift.
An object of class "psp".
Arguments controlling the randomisation and the handling of edge
effects. See rshift.ppp.
Optional. Factor specifying a grouping of the line segments of X,
or NULL indicating that all line segments belong to the same group.
Each group will be shifted together, and
separately from other groups.
Optional. Identifies which groups of the pattern will be shifted,
while other groups are not shifted. A vector of levels of group.
A line segment pattern (object of class "psp").
This operation randomly shifts the locations of the line segments in a line segment pattern.
The function rshift is generic. This function rshift.psp
is the method for line segment patterns.
The line segments of X are first divided into groups,
then the line segments within a group are shifted by a common
random displacement vector. Different groups of line segments are shifted
independently.
If the argument group is present, then this determines the grouping.
Otherwise, all line segments belong to a single group.
The argument group should be a factor, of length equal to the
number of line segments in X.
Alternatively group may be NULL,
which specifies that all line segments of X belong to a single group.
By default, every group of line segments will be shifted.
The argument which indicates that only some of the groups
should be shifted, while other groups should be left unchanged.
which must be a vector of levels of group
indicating which groups are to be shifted.
The displacement vector, i.e. the vector by which the data line segments are shifted, is generated at random. The default behaviour is to generate a displacement vector at random with equal probability for all possible displacements. This means that the \(x\) and \(y\) coordinates of the displacement vector are independent random variables, uniformly distributed over the range of possible coordinates.
Alternatively, the displacement vector can be generated by
another random mechanism, controlled by the arguments
radius, width and height.
if width and height are given, then
the displacement vector is uniformly distributed
in a rectangle of these dimensions, centred at
the origin. The maximum possible displacement in the \(x\)
direction is width/2. The maximum possible displacement in
the \(y\) direction is height/2. The \(x\) and \(y\)
displacements are independent. (If width and height
are actually equal to the dimensions of the observation window,
then this is equivalent to the default.)
if radius is given, then the displacement vector is
generated by choosing a random line segment inside a disc of
the given radius, centred at the origin, with uniform probability
density over the disc. Thus the argument radius determines
the maximum possible displacement distance.
The argument radius is incompatible with the
arguments width and height.
The argument edge controls what happens when
a shifted line segment lies partially or completely
outside the window of X. Currently the only option is
"erode" which specifies that the segments will be clipped
to a smaller window.
The optional argument clip specifies a smaller window
to which the pattern should be restricted.
# NOT RUN {
X <- psp(runif(20), runif(20), runif(20), runif(20), window=owin())
Y <- rshift(X, radius=0.1)
# }
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