rgeos (version 0.3-8)

gIntersection: Geometry Intersections

Description

Function for determining the intersection between the two given geometries

Usage

gIntersection(spgeom1, spgeom2, byid=FALSE, id=NULL, drop_not_poly, drop_lower_td=FALSE)

Arguments

spgeom1, spgeom2

sp objects as defined in package sp

byid

Logical vector determining if the function should be applied across ids (TRUE) or the entire object (FALSE) for spgeom1 and spgeom2

id

Character vector defining id labels for the resulting geometries, if unspecified returned geometries will be labeled based on their parent geometries' labels.

drop_not_poly

deprecated argument, use drop_lower_td

drop_lower_td

default FALSE; if TRUE, objects will be dropped from output GEOMETRYCOLLECTION objects to simplify output if their topological dinension is less than the minimum topological dinension of the input objects.

Details

Returns all spatial intersections as sp objects of the appropriate class. If the geometries do not intersect then an empty geometry is returned.

See Also

gDifference gSymdifference gUnion

Examples

library(maptools)
xx <- readShapeSpatial(system.file("shapes/fylk-val-ll.shp", package="maptools")[1],
 proj4string=CRS("+proj=longlat +datum=WGS84"))
bbxx <- bbox(xx)
wdb_lines <- system.file("share/wdb_borders_c.b", package="maptools")
xxx <- Rgshhs(wdb_lines, xlim=bbxx[1,], ylim=bbxx[2,])$SP
res <-gIntersection(xx, xxx)
plot(xx, axes=TRUE)
plot(xxx, lty=2, add=TRUE)
plot(res, add=TRUE, pch=16,col='red')
pol <- readWKT(paste("POLYGON((-180 -20, -140 55, 10 0, -140 -60, -180 -20),",
 "(-150 -20, -100 -10, -110 20, -150 -20))"))
library(sp)
GT <- GridTopology(c(-175, -85), c(10, 10), c(36, 18))
gr <- as(as(SpatialGrid(GT), "SpatialPixels"), "SpatialPolygons")
try(res <- gIntersection(pol, gr, byid=TRUE))
res <- gIntersection(pol, gr, byid=TRUE, drop_lower_td=TRUE)
# Robert Hijmans difficult intersection case
load(system.file("test_cases/polys.RData", package="rgeos"))
try(res <- gIntersection(a, b, byid=TRUE))
res <- gIntersection(a, b, byid=TRUE, drop_lower_td=TRUE)
unlist(sapply(slot(res, "polygons"), function(p) sapply(slot(p, "Polygons"), slot, "area")))
oT <- get_RGEOS_polyThreshold()
oW <- get_RGEOS_warnSlivers()
oD <- get_RGEOS_dropSlivers()
set_RGEOS_polyThreshold(1e-3)
set_RGEOS_warnSlivers(TRUE)
res1 <- gIntersection(a, b, byid=TRUE, drop_lower_td=TRUE)
unlist(sapply(slot(res1, "polygons"), function(p) sapply(slot(p, "Polygons"), slot, "area")))
set_RGEOS_dropSlivers(TRUE)
res2 <- gIntersection(a, b, byid=TRUE, drop_lower_td=TRUE)
unlist(sapply(slot(res2, "polygons"), function(p) sapply(slot(p, "Polygons"), slot, "area")))
set_RGEOS_dropSlivers(FALSE)
oo <- gUnaryUnion(res1, c(rep("1", 3), "2", "3", "4"))
unlist(sapply(slot(oo, "polygons"), function(p) sapply(slot(p, "Polygons"), slot, "area")))
ooo <- gIntersection(b, oo, byid=TRUE)
gArea(ooo, byid=TRUE)
unlist(sapply(slot(ooo, "polygons"), function(p) sapply(slot(p, "Polygons"), slot, "area")))
set_RGEOS_dropSlivers(TRUE)
ooo <- gIntersection(b, oo, byid=TRUE)
gArea(ooo, byid=TRUE)
unlist(sapply(slot(ooo, "polygons"), function(p) sapply(slot(p, "Polygons"), slot, "area")))
set_RGEOS_polyThreshold(oT)
set_RGEOS_warnSlivers(oW)
set_RGEOS_dropSlivers(oD)