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
Xare diameters.)- …
Optional arguments passed to
as.maskto 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
discto determine the tolerance for the polygonal approximation of each disc. Applies only whenmask=FALSE. Incompatible withnpoly.- npoly
Argument passed to
discto 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))
# }