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.
Usage
spokes(x, y, nrad = 3, nper = 3, fctr = 1.5, Mdefault = 1)
Arguments
- x
- Vector of $x$ coordinates of data points, or a list
with components
x
andy
, or a point pattern (an object of classppp
). - y
- Vector of $y$ coordinates of data points. Ignored
unless
x
is a vector. - 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 data points, the function creates a collection 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 there is only one data point the nearest neighbour distance
is infinite, so the value Mdefault
will be used in place
of M
.
If x
is a point pattern, then the value returned is
also a point pattern, which is clipped to the window
of x
. Hence there may be fewer than
nrad * nper * length(x)
dummy points in the pattern
returned.
Value
- If argument
x
is a point pattern, a point pattern with window equal to that ofx
. Otherwise a list with two componentsx
andy
. In either case the componentsx
andy
of the value are numeric vectors giving the coordinates of the dummy points.
See Also
quad.object
,
quadscheme
,
inside.owin
,
gridcentres
,
stratrand
Examples
dat <- runifrect(10)
plot(dat)
dum <- spokes(dat$x, dat$y)
points(dum$x, dum$y, pch=".")
Q <- quadscheme(dat, dum)