Geometry Relationships - Contains and Within

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Description

Functions for testing whether one geometry contains or is contained within another geometry

Usage

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gContains(spgeom1, spgeom2 = NULL, byid = FALSE, prepared=TRUE,
 returnDense=TRUE, STRsubset=FALSE, checkValidity=FALSE)
gContainsProperly(spgeom1, spgeom2 = NULL, byid = FALSE, returnDense=TRUE,
 checkValidity=FALSE)
gCovers(spgeom1, spgeom2 = NULL, byid = FALSE, returnDense=TRUE, checkValidity=FALSE)
gCoveredBy(spgeom1, spgeom2 = NULL, byid = FALSE, returnDense=TRUE, checkValidity=FALSE)
gWithin(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

STRsubset

logical argument for future use

Value

gContains returns TRUE if none of the point of spgeom2 is outside of spgeom1 and at least one point of spgeom2 falls within spgeom1.

gContainsProperly returns TRUE under the same conditions as gContains with the additional requirement that spgeom2 does not intersect with the boundary of spgeom1. As such any given geometry will Contain itself but will not ContainProperly itself.

gCovers returns TRUE if no point in spgeom2 is outside of spgeom1. This is slightly different from gContains as it does not require a point within spgeom1 which can be an issue as boundaries are not considered to be "within" a geometry, see gBoundary for specifics of geometry boundaries.

gCoveredBy is the converse of gCovers and is equivalent to swapping spgeom1 and spgeom2.

gWithin is the converse of gContains and is equivalent to swapping spgeom1 and spgeom2.

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

References

Helpful information on the subtle differences between these functions: http://lin-ear-th-inking.blogspot.com/2007/06/subtleties-of-ogc-covers-spatial.html

See Also

gCrosses gDisjoint gEquals gEqualsExact gIntersects gOverlaps gRelate gTouches

Examples

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	l1 = readWKT("LINESTRING(0 3,1 1,2 2,3 0)")
	l2 = readWKT("LINESTRING(1 3.5,3 3,2 1)")
	l3 = readWKT("LINESTRING(1 3.5,3 3,4 1)")
	
	pt1 = readWKT("MULTIPOINT(1 1,3 0)")
	pt2 = readWKT("MULTIPOINT(0 3,3 0)")
	pt3 = readWKT("MULTIPOINT(1 1,2 2,3 1)")
	
	p1 = readWKT("POLYGON((0 0,0 2,1 3.5,3 3,4 1,3 0,0 0))")
	p2 = readWKT("POLYGON((1 1,1 2,2 2,2 1,1 1))")

	
	par(mfrow=c(2,3))
	plot(l1,col='blue');plot(pt1,add=TRUE,pch=16)
	title(paste("Contains:",gContains(l1,pt1),
				"\nContainsProperly:",gContainsProperly(l1,pt1),
				"\nCovers:",gCovers(l1,pt1)))
	
	plot(l1,col='blue');plot(pt2,add=TRUE,pch=16)
	title(paste("Contains:",gContains(l1,pt2),
				"\nContainsProperly:",gContainsProperly(l1,pt2),
				"\nCovers:",gCovers(l1,pt2)))
	
	plot(p1,col='blue',border='blue');plot(pt3,add=TRUE,pch=16)
	title(paste("Contains:",gContains(p1,pt3),
				"\nContainsProperly:",gContainsProperly(p1,pt3),
				"\nCovers:",gCovers(p1,pt3)))
	
	plot(p1,col='blue',border='blue');plot(l2,lwd=2,add=TRUE,pch=16)
	title(paste("Contains:",gContains(p1,l2),
				"\nContainsProperly:",gContainsProperly(p1,l2),
				"\nCovers:",gCovers(p1,l2)))

	plot(p1,col='blue',border='blue');plot(l3,lwd=2,add=TRUE,pch=16)
	title(paste("Contains:",gContains(p1,l3),
				"\nContainsProperly:",gContainsProperly(p1,l3),
				"\nCovers:",gCovers(p1,l3)))

	plot(p1,col='blue',border='blue');plot(p2,col='black',add=TRUE,pch=16)
	title(paste("Contains:",gContains(p1,p2),
				"\nContainsProperly:",gContainsProperly(p1,p2),
				"\nCovers:",gCovers(p1,p2)))
	
	

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