Polygonal Approximation of a Disc/Circle

Generates a polygon representing a disc/circle (in planar coordinates) as an object of one of three possible classes: "Polygon", "owin", or -- if gpclib is 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.geom'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" and this S4 class is neither registered nor available via loading gpclib, only the

pts slot of a "gpc.poly" is returned with a warning.

Author

Sebastian Meyer
This function is inspired by the disc function from package spatstat.geom.

See also

disc in package spatstat.geom.

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 (surveillance.options("gpclib") && requireNamespace("gpclib")) {
    disc3 <- discpoly(c(0,0), 5, npoly=64, class = "gpc.poly")
    print(disc3)
    plot(disc3, add=TRUE, poly.args=list(border=4))
}

## to only _draw_ a circle
symbols(0, 0, circles=5, inches=FALSE, add=TRUE, fg=5)