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" from package sp, "owin" from package spatstat.geom, or "gpc.poly" from gpclib (if available).

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 not yet registered in the current R session (by loading gpclib beforehand), only the pts slot of a "gpc.poly" is returned with a warning.

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")
disc3 <- discpoly(c(0,0), 5, npoly=64, class = "gpc.poly")  # may warn

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

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

str(disc3)  # a list or a formal "gpc.poly" (if gpclib is available)
if (is(disc3, "gpc.poly")) {
  plot(disc3, add=TRUE, poly.args=list(border=4))
} else {
  lines(disc3[[1]], col=4)
}

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