rgeos (version 0.3-5)

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

Description

A class for representing polygons composed of multiple contours, some of which may be holes.

Objects from the Class

Objects can be created by calls of the form new("gpc.poly", ...) or by reading in from a file using read.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-gpc/ex-poly1.txt", package = "rgeos"))
p2 <- read.polyfile(system.file("poly-ex-gpc/ex-poly2.txt", package = "rgeos"))

## 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))

## Coerce from a matrix
x <- 
structure(c(0.0934073560027759, 0.192713393476752, 0.410062456627342, 
0.470020818875781, 0.41380985426787, 0.271408743927828, 0.100902151283831, 
0.0465648854961832, 0.63981588032221, 0.772382048331416,
0.753739930955121, 0.637744533947066, 0.455466052934407,
0.335327963176065, 0.399539700805524, 
0.600460299194476), .Dim = c(8, 2))
y <- 
structure(c(0.404441360166551, 0.338861901457321, 0.301387925052047, 
0.404441360166551, 0.531852879944483, 0.60117973629424, 0.625537820957668, 
0.179976985040276, 0.341542002301496, 0.445109321058688,
0.610817031070196, 0.596317606444189, 0.459608745684695,
0.215189873417722), .Dim = c(7, 2))

x1 <- as(x, "gpc.poly")
y1 <- as(y, "gpc.poly")

plot(append.poly(x1, y1))
plot(intersect(x1, y1), poly.args = list(col = 2), add = TRUE)

## Show the triangulation
#plot(append.poly(x1, y1))
#triangles <- triangulate(append.poly(x1,y1))
#for (i in 0:(nrow(triangles)/3 - 1)) 
#    polygon(triangles[3*i + 1:3,], col="lightblue")