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.
spokes(x, y, nrad = 3, nper = 3, fctr = 1.5, Mdefault = 1)
- Vector of $x$ coordinates of data points, or a list
y, or a point pattern (an object of class
- Vector of $y$ coordinates of data points. Ignored
xis a vector.
- Number of radii emanating from each data point.
- Number of dummy points per radius.
- Scale factor.
Length of largest spoke radius is
fctr * Mwhere
Mis the mean nearest neighbour distance for the data points.
- Value of
Mto be used if
xhas length 1.
This function is useful in creating dummy points for quadrature
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
nper dummy points
equally spaced along each radius.
The (equal) spacing of dummy points along each radius is
controlled by the factor
The distance from a data point to the furthest of its associated
dummy points is
fctr * M
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
x is a point pattern, then the value returned is
also a point pattern, which is clipped to the window
x. Hence there may be fewer than
nrad * nper * length(x) dummy points in the pattern
- If argument
xis a point pattern, a point pattern with window equal to that of
x. Otherwise a list with two components
y. In either case the components
yof the value are numeric vectors giving the coordinates of the dummy points.
dat <- runifrect(10) plot(dat) dum <- spokes(dat$x, dat$y) points(dum$x, dum$y, pch=".") Q <- quadscheme(dat, dum)