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.

Slots

pts

Object of class “list”. Actually, pts is a list of lists with length equal to the number of contours in the "gpc.poly" object. Each element of pts is a list of length 3 with names x, y, and hole. x and y are vectors containing the x and y coordinates, respectively, while hole is a logical indicating whether or not the contour is a hole.

Methods

[

signature(x = "gpc.poly"): ...

append.poly

signature(x = "gpc.poly", y = "gpc.poly"): ...

area.poly

signature(object = "gpc.poly"): ...

coerce

signature(from = "matrix", to = "gpc.poly"): ...

coerce

signature(from = "data.frame", to = "gpc.poly"): ...

coerce

signature(from = "gpc.poly", to = "matrix"): ...

coerce

signature(from = "gpc.poly", to = "numeric"): ...

coerce

signature(from = "numeric", to = "gpc.poly"): ...

coerce

signature(from = "list", to = "gpc.poly"): ...

get.bbox

signature(x = "gpc.poly"): ...

get.pts

signature(object = "gpc.poly"): ...

intersect

signature(x = "gpc.poly", y = "gpc.poly"): ...

plot

signature(x = "gpc.poly"): The argument poly.args can be used to pass a list of additional arguments to be passed to the underlying polygon call.

scale.poly

signature(x = "gpc.poly"): ...

setdiff

signature(x = "gpc.poly", y = "gpc.poly"): ...

show

signature(object = "gpc.poly"): Scale x and y coordinates by amount xscale and yscale. By default xscale equals yscale.

union

signature(x = "gpc.poly", y = "gpc.poly"): ...

tristrip

signature(x = "gpc.poly"): ...

triangulate

signature(x = "gpc.poly"): ...

Note

The class "gpc.poly.nohole" is identical to "gpc.poly" except the hole flag for each contour of a "gpc.poly.nohole" object is always FALSE.

Author(s)

Roger D. Peng

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))

## 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")