Polygon Region

Points inside polygon region.

inpolygon(x, y, xp, yp, boundary = FALSE)

Arguments

x, y

x-, y-coordinates of points to be tested for being inside the polygon region.

xp, yp

coordinates of the vertices specifying the polygon.

boundary

Logical; does the boundary belong to the interior.

Details

For a polygon defined by points (xp, yp), determine if the points (x, y) are inside or outside the polygon. The boundary can be included or excluded (default) for the interior.

Value

Logical vector, the same length as x.

References

Hormann, K., and A. Agathos (2001). The Point in Polygon Problem for Arbitrary Polygons. Computational Geometry, Vol. 20, No. 3, pp. 131–144.

Note

Special care taken for points on the boundary.

See also

polygon

Examples

xp <- c(0.5, 0.75, 0.75, 0.5, 0.5)
yp <- c(0.5, 0.5, 0.75, 0.75, 0.5)
x <- c(0.6, 0.75, 0.6, 0.5)
y <- c(0.5, 0.6, 0.75, 0.6)
inpolygon(x, y, xp, yp, boundary = FALSE)  # FALSE
#> [1] FALSE FALSE FALSE FALSE
inpolygon(x, y, xp, yp, boundary = TRUE)   # TRUE
#> [1] TRUE TRUE TRUE TRUE

if (FALSE) { # \dontrun{
pg <- matrix(c(0.15, 0.75, 0.25, 0.45, 0.70,
               0.80, 0.35, 0.55, 0.20, 0.90), 5, 2)
plot(c(0, 1), c(0, 1), type="n")
polygon(pg[,1], pg[,2])
P <- matrix(runif(20000), 10000, 2)
R <- inpolygon(P[, 1], P[, 2], pg[, 1], pg[,2])
clrs <- ifelse(R, "red", "blue")
points(P[, 1], P[, 2], pch = ".", col = clrs)} # }