# ellipse

##### Elliptical Window.

Create an elliptical window.

##### Usage

`ellipse(a, b, centre=c(0,0), phi=0, …, mask=FALSE, npoly = 128)`

##### Arguments

- a,b
The half-lengths of the axes of the ellipse.

- centre
The centre of the ellipse.

- phi
The (anti-clockwise) angle through which the ellipse should be rotated (about its centre) starting from an orientation in which the axis of half-length

`a`

is horizontal.- mask
Logical value controlling the type of approximation to a perfect ellipse. See Details.

- …
Arguments passed to

`as.mask`

to determine the pixel resolution, if`mask`

is`TRUE`

.- npoly
The number of edges in the polygonal approximation to the ellipse.

##### Details

This command creates a window object representing an ellipse with the given centre and axes.

By default, the ellipse is
approximated by a polygon with `npoly`

edges.

If `mask=TRUE`

, then the ellipse is approximated by a binary pixel
mask. The resolution of the mask is controlled by
the arguments `…`

which are passed to `as.mask`

.

The arguments `a`

and `b`

must be single positive numbers.
The argument `centre`

specifies the ellipse centre: it can be either
a numeric vector of length 2 giving the coordinates,
or a `list(x,y)`

giving the coordinates of exactly one point, or a
point pattern (object of class `"ppp"`

) containing exactly one point.

##### Value

An object of class `owin`

(either of type “polygonal”
or of type “mask”) specifying an elliptical window.

##### See Also

##### Examples

```
# NOT RUN {
W <- ellipse(a=5,b=2,centre=c(5,1),phi=pi/6)
plot(W,lwd=2,border="red")
WM <- ellipse(a=5,b=2,centre=c(5,1),phi=pi/6,mask=TRUE,dimyx=512)
plot(WM,add=TRUE,box=FALSE)
# }
```

*Documentation reproduced from package spatstat, version 1.55-1, License: GPL (>= 2)*