Geometry Relationships - Intersects and Disjoint

Function for testing if the geometries have at least one point in common or no points in common

gIntersects(spgeom1, spgeom2 = NULL, byid = FALSE, prepared=TRUE,
 returnDense=TRUE, checkValidity=FALSE)
gDisjoint(spgeom1, spgeom2 = NULL, byid = FALSE, returnDense=TRUE,
 checkValidity=FALSE)

Arguments

spgeom1, spgeom2: sp objects as defined in package sp. If spgeom2 is NULL then spgeom1 is compared to itself.
byid: Logical vector determining if the function should be applied across ids (TRUE) or the entire object (FALSE) for spgeom1 and spgeom2
prepared: Logical determining if prepared geometry (spatially indexed) version of the GEOS function should be used. In general prepared geometries should be faster than the alternative.
returnDense: default TRUE, if false returns a list of the length of spgeom1 of integer vectors listing the 1:length(spgeom2) indices which would be TRUE in the dense logical matrix representation; useful when the sizes of the byid=TRUE returned matrix is very large and it is sparse; essential when the returned matrix would be too large
checkValidity: default FALSE; error meesages from GEOS do not say clearly which object fails if a topology exception is encountered. If this argument is TRUE, gIsValid is run on each in turn in an environment in which object names are available. If objects are invalid, this is reported and those affected are named

Value

gIntersects returns TRUE if spgeom1 and spgeom2 have at least one point in common.

gDisjoint returns TRUE if spgeom1 and spgeom2 have no points in common.

Both return a conforming logical matrix if byid = TRUE.

Note

Error messages from GEOS, in particular topology exceptions, report 0-based object order, so geom 0 is spgeom1, and geom 1 is spgeom2.

Author

Roger Bivand & Colin Rundel

Examples

  p1 = readWKT("POLYGON((0 0,1 0,1 1,0 1,0 0))")
  p2 = readWKT("POLYGON((0.5 1,0 2,1 2,0.5 1))")
  p3 = readWKT("POLYGON((0.5 0.5,0 1.5,1 1.5,0.5 0.5))")

  l1 = readWKT("LINESTRING(0 3,1 1,2 2,3 0)")
  l2 = readWKT("LINESTRING(1 3.5,3 3,2 1)")
  l3 = readWKT("LINESTRING(-0.1 0,-0.1 1.1,1 1.1)")
  
  pt1 = readWKT("MULTIPOINT(1 1,3 0,2 1)")
  pt2 = readWKT("MULTIPOINT(0 3,3 0,2 1)")
  pt3 = readWKT("MULTIPOINT(-0.2 0,1 -0.2,1.2 1,0 1.2)")

  
  par(mfrow=c(3,2))
  plot(p1,col='blue',border='blue',ylim=c(0,2.5));plot(p2,col='black',add=TRUE,pch=16)
  title(paste("Intersects:",gIntersects(p1,p2),
        "\nDisjoint:",gDisjoint(p1,p2)))
  
  plot(p1,col='blue',border='blue',ylim=c(0,2.5));plot(p3,col='black',add=TRUE,pch=16)
  title(paste("Intersects:",gIntersects(p1,p3),
        "\nDisjoint:",gDisjoint(p1,p3)))
        
  plot(l1,col='blue');plot(pt1,add=TRUE,pch=16)
  title(paste("Intersects:",gIntersects(l1,pt1),
        "\nDisjoint:",gDisjoint(l1,pt1)))
  
  plot(l1,col='blue');plot(pt2,add=TRUE,pch=16)
  title(paste("Intersects:",gIntersects(l1,pt2),
        "\nDisjoint:",gDisjoint(l1,pt2)))
  
  plot(p1,col='blue',border='blue',xlim=c(-0.5,2),ylim=c(0,2.5))
  plot(l3,lwd=2,col='black',add=TRUE)
  title(paste("Intersects:",gIntersects(p1,l3),
        "\nDisjoint:",gDisjoint(p1,l3)))
  
  plot(p1,col='blue',border='blue',xlim=c(-0.5,2),ylim=c(-0.5,2))
  plot(pt3,pch=16,col='black',add=TRUE)
  title(paste("Intersects:",gIntersects(p1,pt3),
        "\nDisjoint:",gDisjoint(p1,pt3)))


# Michael Chirico bug report and fix 2019-08-16
  SP1 = SpatialPoints(
    cbind(c(.25, .75), c(.75, .25))  )
  SP2 = SpatialPolygons(list(
    Polygons(list(Polygon(cbind(c(0, 0, 1, 1), c(0, 1, 1, 0)))), ID = 'a'),
    Polygons(list(Polygon(cbind(c(1, 1, 2, 2), c(1, 2, 2, 1)))), ID = 'b')
  ))

  gIntersects(SP1, SP2, byid = c(TRUE, FALSE))
#>         1    2
#> [1,] TRUE TRUE
  gIntersects(SP1, SP2, byid = c(TRUE, TRUE))
#>       1     2
#> a  TRUE  TRUE
#> b FALSE FALSE
        gIntersects(SP1, SP2, byid = c(FALSE, TRUE))
#>    [,1]
#> a  TRUE
#> b FALSE
        gIntersects(SP1, SP2, byid = c(FALSE, FALSE))
#> [1] TRUE