Generates a default pattern of dummy points for use in a quadrature scheme.
default.dummy(X, nd, random=FALSE, ntile=NULL, npix=NULL,
quasi=FALSE, ..., eps=NULL, verbose=FALSE)A point pattern (an object of class "ppp",
see ppp.object) containing the dummy points.
This function provides a sensible default for the dummy points in a quadrature scheme.
A quadrature scheme consists of
the original data point pattern, an additional pattern of dummy points,
and a vector of quadrature weights for all these points.
See quad.object for further information about
quadrature schemes.
If random and quasi are both false (the default),
then the function creates dummy points
in a regular nd[1] by nd[1] rectangular grid.
If random is true and quasi is false,
then the frame of the window is divided into
an nd[1] by nd[1] array of tiles, and one dummy point
is generated at random inside each tile.
If quasi is true, a quasirandom pattern of
nd[1] * nd[2] points is generated.
In all cases, the four corner points of the frame of the window
are added. Then if the window is not rectangular, any dummy points
lying outside it are deleted.
If nd is missing, a default value is computed by
the undocumented internal function default.n.tiling,
using information about the data pattern X,
and other arguments and settings.
The default value of nd is always greater than or equal to
spatstat.options("ndummy.min")
and greater than or equal to 10 * ceiling(2 * sqrt(npoints(X))/10),
and satisfies some other constraints.
The default is designed so that model-fitting is relatively fast and stable,
rather than highly accurate.
Alternative functions for creating dummy patterns
include corners,
gridcentres,
stratrand and
spokes.
quad.object,
quadscheme,
corners,
gridcentres,
stratrand,
spokes
P <- simdat
D <- default.dummy(P, 100)
plot(D)
Q <- quadscheme(P, D, "grid")
if(interactive()) {plot(union.quad(Q))}
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