spatstat.geom (version 3.6-0)

disc: Circular Window

Description

Creates a circular window

Usage

disc(radius=1, centre=c(0,0), ...,
      mask=FALSE, npoly=128, delta=NULL,
      type=c("inscribed", "circumscribed", "approx"),
      metric=NULL)

Value

An object of class "owin" (see owin.object) specifying a window.

Arguments

radius

Radius of the circle.

centre

The centre of the circle.

mask

Logical flag controlling the type of approximation to a perfect circle. See Details.

npoly

Number of edges of the polygonal approximation, if mask=FALSE. Incompatible with delta.

delta

Tolerance of polygonal approximation: the length of arc that will be replaced by one edge of the polygon. Incompatible with npoly.

type

Optional. Character string (partially matched) indicating whether the polygonal approximation should be an inscribed polygon (type="inscribed", the default), a circumscribed polygon (type="circumscribed") or a polygon which is between the inscribed and circumscribed polygons (type="approx").

...

Arguments passed to as.mask determining the pixel resolution, if mask=TRUE.

metric

Optional. A distance metric (object of class "metric"). The disc with respect to this metric will be computed.

Author

Adrian Baddeley , Rolf Turner and Ege Rubak .

Details

This command creates a window object representing a disc, with the given radius and centre.

By default, the circle is approximated by a polygon with npoly edges.

If mask=TRUE, then the disc is approximated by a binary pixel mask. The resolution of the mask is controlled by the arguments ... which are passed to as.mask.

The argument radius must be a single positive number. The argument centre specifies the disc 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.

If type="inscribed" (the default), the polygon is inscribed in the perfect circle of radius radius, that is, all vertices of the polygon are points on the circle, and the circle contains the polygon. If type="circumscribed", the polygon is circumscribed around the circle, that is, the polygon contains the circle, and all edges of the polygon are tangent to the circle. If type="approx", the polygon is constructed to lie between the inscribed and circumscribed polygons, giving a better approximation to the circle.

If the argument metric is given, it should be a distance metric (object of class "metric"). The disc with respect to this metric will be computed.

See Also

ellipse, discs, owin.object, owin, as.mask

Examples

 # unit disc
 W <- disc()
 # disc of radius 3 centred at x=10, y=5
 W <- disc(3, c(10,5))
 #
 plot(disc())
 plot(disc(mask=TRUE))
 # nice smooth circle
 plot(disc(npoly=256))
 # how to control the resolution of the mask
 plot(disc(mask=TRUE, dimyx=256))
 # check accuracy of approximation
 area(disc())/pi
 area(disc(mask=TRUE))/pi
 # inscribed and circumscribed
 plot(disc(npoly=256), main="Inscribed and circumscribed", border="green")
 plot(disc(npoly=7, type="i"), add=TRUE, border="red")
 plot(disc(npoly=7, type="c"), add=TRUE, border="blue")
 plot(disc(npoly=7, type="a"), add=TRUE, border="grey")