R: Union of Discs

discs {spatstat.geom} | R Documentation

## Union of Discs

### Description

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, if `mask=TRUE`.
`separate` | Logical. If `TRUE`, the result is a list containing each disc as a separate entry. If `FALSE` (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. If `FALSE`, the result is a polygonal window. Applies only when `separate=FALSE`.
`trim` | Logical value indicating whether to restrict the result to the original window of the `centres`. Applies only when `separate=FALSE`.
`delta` | Argument passed to `disc` to determine the tolerance for the polygonal approximation of each disc. Applies only when `mask=FALSE`. Incompatible with `npoly`.
`npoly` | Argument passed to `disc` to determine the number of edges in the polygonal approximation of each disc. Applies only when `mask=FALSE`. Incompatible with `delta`.

### 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.

### Author(s)

Adrian Baddeley Adrian.Baddeley@curtin.edu.au, Rolf Turner r.turner@auckland.ac.nz and Ege Rubak rubak@math.aau.dk.

### See Also

`disc`, `union.owin`

### Examples

      plot(discs(anemones, mask=TRUE, eps=0.5))

[Package spatstat.geom version 2.3-2 Index]