Draw a Circle

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Description

Functions to create and draw a circle.

Usage

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grid.circle(x=0.5, y=0.5, r=0.5, default.units="npc", name=NULL,
            gp=gpar(), draw=TRUE, vp=NULL)
circleGrob(x=0.5, y=0.5, r=0.5, default.units="npc", name=NULL,
            gp=gpar(), vp=NULL)

Arguments

x

A numeric vector or unit object specifying x-locations.

y

A numeric vector or unit object specifying y-locations.

r

A numeric vector or unit object specifying radii.

default.units

A string indicating the default units to use if x, y, width, or height are only given as numeric vectors.

name

A character identifier.

gp

An object of class gpar, typically the output from a call to the function gpar. This is basically a list of graphical parameter settings.

draw

A logical value indicating whether graphics output should be produced.

vp

A Grid viewport object (or NULL).

Details

Both functions create a circle grob (a graphical object describing a circle), but only grid.circle() draws the circle (and then only if draw is TRUE).

The radius may be given in any units; if the units are relative (e.g., "npc" or "native") then the radius will be different depending on whether it is interpreted as a width or as a height. In such cases, the smaller of these two values will be the result. To see the effect, type grid.circle() and adjust the size of the window.

What happens for very small radii is device-dependent: the circle may become invisible or be shown at a fixed minimum size. Circles of zero radius will not be plotted.

Value

A circle grob. grid.circle() returns the value invisibly.

Warning

Negative values for the radius are silently converted to their absolute value.

Author(s)

Paul Murrell

See Also

Grid, viewport

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