gpclib (version 1.0-1)

gpc.poly-class: Class "gpc.poly"

Description

A class for polygons consisting of multiple contours.

Objects from the Class

Objects can be created by using the function read.polyfile or by coercing from another data type. One can also use new("gpc.poly", ...).

See Also

read.polyfile, write.polyfile

Examples

## Make some random polygons
set.seed(100)
a <- cbind(rnorm(100), rnorm(100))
a <- a[chull(a), ]

## Convert `a' from matrix to "gpc.poly"
a <- as(a, "gpc.poly")

b <- cbind(rnorm(100), rnorm(100))
b <- as(b[chull(b), ], "gpc.poly")

## More complex polygons with an intersection
p1 <- read.polyfile(system.file("poly-ex/ex-poly1.txt", package = "gpclib"))
p2 <- read.polyfile(system.file("poly-ex/ex-poly2.txt", package = "gpclib"))

## Plot both polygons and highlight their intersection in red
plot(append.poly(p1, p2))
plot(intersect(p1, p2), poly.args = list(col = 2), add = TRUE)

## Highlight the difference p1 \ p2 in green
plot(setdiff(p1, p2), poly.args = list(col = 3), add = TRUE)

## Highlight the difference p2 \ p1 in blue
plot(setdiff(p2, p1), poly.args = list(col = 4), add = TRUE)

## Plot the union of the two polygons
plot(union(p1, p2))

## Take the non-intersect portions and create a new polygon
## combining the two contours
p.comb <- append.poly(setdiff(p1, p2), setdiff(p2, p1))
plot(p.comb, poly.args = list(col = 2, border = 0))