surveillance (version 1.20.3)

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)

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.

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?

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 (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)