disc | R Documentation |
Creates a circular window
disc(radius=1, centre=c(0,0), ...,
mask=FALSE, npoly=128, delta=NULL,
metric=NULL)
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 |
delta |
Tolerance of polygonal approximation: the length of arc
that will be replaced by one edge of the polygon.
Incompatible with |
... |
Arguments passed to |
metric |
Optional. A distance metric (object of class |
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 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.
An object of class "owin"
(see owin.object
)
specifying a window.
This function can also be used to generate regular polygons,
by setting npoly
to a small integer value. For example
npoly=5
generates a pentagon and npoly=13
a triskaidecagon.
.
ellipse
,
discs
,
owin.object
,
owin
,
as.mask
# 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
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