# 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, 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.

##### See Also

##### Examples

```
# NOT RUN {
plot(discs(anemones, mask=TRUE, eps=0.5))
# }
```

*Documentation reproduced from package spatstat, version 1.56-1, License: GPL (>= 2)*