inlmisc (version 0.5.5)

SetPolygons: Overlay Multi-Polygon Objects

Description

Calculate the intersection or difference between two multi-polygon objects.

Usage

SetPolygons(x, y, cmd = c("gIntersection", "gDifference"), buffer.width = NA)

Arguments

x

'SpatialPolygons*'. Multi-polygon object

y

'SpatialPolygons*' or 'Extent'. Multi-polygon object

cmd

'character' string. Specifying "gIntersection", the default, cuts out portions of the x polygons that overlay the y polygons. If "gDifference" is specified, only those portions of the x polygons falling outside the y polygons are copied to the output polygons.

buffer.width

'numeric' number. Expands or contracts the geometry of y to include the area within the specified width, see gBuffer. Specifying NA, the default, indicates no buffer.

Value

An object of class 'SpatialPolygons*'.

Details

This function tests if the resulting geometry is valid. If invalid, an attempt is made to make the geometry valid by zero-width buffering.

Examples

# NOT RUN {
m1a <- rbind(c(17.5, 55.1),
             c(24.7, 55.0),
             c(22.6, 61.1),
             c(16.5, 59.7),
             c(17.5, 55.1))
m1b <- m1a
m1b[, 1] <- m1b[, 1] + 11
p1 <- list(sp::Polygon(m1a, FALSE), sp::Polygon(m1b, FALSE))
p1 <- sp::SpatialPolygons(list(sp::Polygons(p1, 1)))
sp::plot(p1, col = "blue")

m2a <- rbind(c(19.6, 60.0),
             c(35.7, 58.8),
             c(28.2, 64.4),
             c(19.6, 60.0))
m2b <- rbind(c(20.6, 56.2),
             c(30.9, 53.8),
             c(27.3, 51.4),
             c(20.6, 56.2))
p2 <- list(sp::Polygon(m2a, FALSE), sp::Polygon(m2b, FALSE))
p2 <- sp::SpatialPolygons(list(sp::Polygons(p2, 2)))
sp::plot(p2, col = "red", add = TRUE)

p <- SetPolygons(p1, p2, "gIntersection")
sp::plot(p, col = "green", add = TRUE)

p <- SetPolygons(p2, p1, "gDifference")
sp::plot(p, col = "purple", add = TRUE)

# }