gIntersects {rgeos} | R Documentation

## Geometry Relationships - Intersects and Disjoint

### Description

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

### Usage

    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(s)

Roger Bivand & Colin Rundel

### See Also

`gContains` `gContainsProperly` `gCovers` `gCoveredBy` `gCrosses` `gEquals` `gEqualsExact` `gOverlaps` `gRelate` `gTouches` `gWithin`

### 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)))

[Package rgeos version 0.5-1 Index]