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
is false (the default),
then the function creates dummy points
in an nx
by ny
rectangular grid.
If random
is true, then the frame of the window is divided into
an nx
by ny
array of tiles, and one dummy point
is generated at random inside each tile.
In either case, 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 nx
is missing, a default value (depending on the
data pattern X
) is computed by default.ngrid
.
If ny
is missing, it defaults to nx
.
Alternative functions for creating dummy patterns
include corners
,
gridcentres
,
stratrand
and
spokes
.