R: Elliptical Window.

ellipse {spatstat} | R Documentation

## Elliptical Window.

### Description

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.

### Author(s)

Adrian Baddeley Adrian.Baddeley@curtin.edu.au

and Rolf Turner r.turner@auckland.ac.nz

### See Also

`disc`, `owin.object`, `owin`, `as.mask`

### Examples

      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)

[Package spatstat version 1.54-0 Index]