spokes
Spokes pattern of dummy points
Generates a pattern of dummy points in a window, given a data point pattern. The dummy points lie on the radii of circles emanating from each data point.
- Keywords
- spatial
Usage
spokes(x, y, nrad = 3, nper = 3, fctr = 1.5, Mdefault = 1)
Arguments
- x
- Vector of $x$ coordinates of data points.
- y
- Vector of $y$ coordinates of data points.
- nrad
- Number of radii emanating from each data point.
- nper
- Number of dummy points per radius.
- fctr
- Scale factor.
Length of largest spoke radius is
fctr * M
whereM
is the mean nearest neighbour distance for the data points. - Mdefault
- Value of
M
to be used ifx
has length 1.
Details
This function is useful in creating dummy points for quadrature
schemes (see quadscheme
).
Given the point pattern specified by the vectors
x
and y
, the function
creates a pattern of nrad * nper * length(x)
dummy points.
Around each data point (x[i],y[i])
there are
nrad * nper
dummy points, lying on nrad
radii
emanating from (x[i],y[i])
, with nper
dummy points
equally spaced along each radius.
The (equal) spacing of dummy points along each radius is
controlled by the factor fctr
.
The distance from a data point to the furthest of its associated
dummy points is fctr * M
where M
is the mean nearest neighbour distance
for the data points.
If the point pattern specified by x
and y
contains
only one point, the nearest neighbour distance is infinite,
so the value Mdefault
will be used in place of M
.
Value
- A list with two components
x
andy
, which are numeric vectors giving the coordinates of the dummy points.
See Also
quad.object
,
quadscheme
,
inside.owin
,
gridcentres
,
stratrand
Examples
library(spatstat)
dat <- runifrect(10)
plot(dat)
dum <- spokes(dat$x, dat$y)
points(dum$x, dum$y, pch=".")
Q <- quadscheme(dat, dum)