surveillance (version 1.12.1)

discpoly: Polygonal Approximation of a Disc/Circle

Description

Generates a polygon representing a disc/circle (in planar coordinates) as an object of one of three possible classes: "Polygon", "owin", or -- if rgeos (or gpclib) are available -- "gpc.poly".

Usage

discpoly(center, radius, npoly = 64,
         class = c("Polygon", "owin", "gpc.poly"),
         hole = FALSE)

Arguments

center

numeric vector of length 2 (center coordinates of the circle).

radius

single numeric value (radius of the circle).

npoly

single integer. Number of edges of the polygonal approximation.

class

class of the resulting polygon (partial name matching applies). For "owin", this is just a wrapper around spatstat's own disc function.

hole

logical. Does the resulting polygon represent a hole?

Value

• A polygon of class class representing a circle/disc with npoly edges accuracy. If class="gpc.poly" although this formal class is not currently defined (and rgeos is not available), only the pts slot of a "gpc.poly" is returned with a warning.

See Also

disc in package spatstat.

Examples

## Construct circles with increasing accuracy and of different spatial classes
disc1 <- discpoly(c(0,0), 5, npoly=4, class = "owin")
disc2 <- discpoly(c(0,0), 5, npoly=16, class = "Polygon")

## Look at the results
print(disc1)
plot(disc1, axes=TRUE, main="", border=2)

print(disc2)
lines(disc2, col=3)

if (requireNamespace("rgeos")) { # for the "gpc.poly" class definition
    disc3 <- discpoly(c(0,0), 5, npoly=64, class = "gpc.poly")
    print(disc3)
    plot(disc3, add=TRUE, poly.args=list(border=4))
}

## if one only wants to _draw_ a circle without an object behind
symbols(0, 0, circles=5, inches=FALSE, add=TRUE, fg=5)