discs
Union of Discs
Make a spatial region composed of discs with given centres and radii.
Usage
discs(centres, radii = marks(centres)/2, …,
separate = FALSE, mask = FALSE, trim = TRUE,
delta = NULL, npoly=NULL)
Arguments
- centres
Point pattern giving the locations of centres for the discs.
- radii
Vector of radii for each disc, or a single number giving a common radius. (Notice that the default assumes that the marks of
X
are diameters.)- …
Optional arguments passed to
as.mask
to determine the pixel resolution, ifmask=TRUE
.- separate
Logical. If
TRUE
, the result is a list containing each disc as a separate entry. IfFALSE
(the default), the result is a window obtained by forming the union of the discs.- mask
Logical. If
TRUE
, the result is a binary mask window. IfFALSE
, the result is a polygonal window. Applies only whenseparate=FALSE
.- trim
Logical value indicating whether to restrict the result to the original window of the
centres
. Applies only whenseparate=FALSE
.- delta
Argument passed to
disc
to determine the tolerance for the polygonal approximation of each disc. Applies only whenmask=FALSE
. Incompatible withnpoly
.- npoly
Argument passed to
disc
to determine the number of edges in the polygonal approximation of each disc. Applies only whenmask=FALSE
. Incompatible withdelta
.
Details
This command is typically applied to a marked point pattern
dataset X
in which the marks represent the sizes of objects.
The result is a spatial region representing the space occupied by
the objects.
If the marks of X
represent the diameters of circular objects,
then the result of discs(X)
is a spatial region constructed by taking discs, of the specified
diameters, centred at the points of X
, and forming the union
of these discs. If the marks of X
represent the areas of
objects, one could take discs(X, sqrt(marks(X)/pi))
to produce discs of equivalent area.
A fast algorithm is used to compute the result as a binary mask, when
mask=TRUE
. This option is recommended unless polygons are
really necessary.
If mask=FALSE
, the discs will be constructed as polygons
by the function disc
. To avoid computational problems,
by default, the discs will all be constructed using
the same physical tolerance value delta
passed to disc
. The default is such that the smallest
disc will be approximated by a 16-sided polygon.
(The argument npoly
should not normally be used, to avoid
computational problems arising with small radii.)
Value
If separate=FALSE
, a window (object of class "owin"
).
If separate=TRUE
, a list of windows.
See Also
Examples
# NOT RUN {
plot(discs(anemones, mask=TRUE, eps=0.5))
# }