gCrosses {rgeos} | R Documentation

## Geometry Relationships - Crosses and Overlaps

### Description

Functions for testing whether geometries share some but not all interior points

### Usage

    	gCrosses(spgeom1, spgeom2 = NULL, byid = FALSE, returnDense=TRUE,
     checkValidity=FALSE)
    	gOverlaps(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
`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

`gCrosses` returns TRUE when the geometries share some but not all interior points, and the dimension of the intersection is less than that of at least one of the geometries.

`gOverlaps` returns TRUE when the geometries share some but not all interior points, and the intersection has the same dimension as the geometries themselves.

### 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` `gDisjoint` `gEquals` `gEqualsExact` `gIntersects` `gRelate` `gTouches` `gWithin`

### Examples

    	l1 = readWKT("LINESTRING(0 3,1 1,2 2,3 0)")
    	l2 = readWKT("LINESTRING(0 0.5,1 1,2 2,3 2.5)")
    	l3 = readWKT("LINESTRING(1 3,1.5 1,2.5 2)")

    	pt1 = readWKT("MULTIPOINT(1 1,3 0)")
    	pt2 = readWKT("MULTIPOINT(1 1,3 0,1 2)")

    	p1 = readWKT("POLYGON((0 0,0 2,1 3.5,3 3,4 1,3 0,0 0))")
    	p2 = readWKT("POLYGON((2 2,3 4,4 1,4 0,2 2))")

    	par(mfrow=c(2,3))
    	plot(l1,col='blue');plot(pt1,add=TRUE,pch=16)
    	title(paste("Crosses:",gCrosses(l1,pt1),
    				"\nOverlaps:",gOverlaps(l1,pt1)))

    	plot(l1,col='blue');plot(pt2,add=TRUE,pch=16)
    	title(paste("Crosses:",gCrosses(l1,pt2),
    				"\nOverlaps:",gOverlaps(l1,pt2)))

    	plot(l1,col='blue');plot(l2,add=TRUE)
    	title(paste("Crosses:",gCrosses(l1,l2),
    				"\nOverlaps:",gOverlaps(l1,l2)))

    	plot(l1,col='blue');plot(l3,add=TRUE)
    	title(paste("Crosses:",gCrosses(l1,l3),
    				"\nOverlaps:",gOverlaps(l1,l3)))

    	plot(p1,border='blue',col='blue');plot(l1,add=TRUE)
    	title(paste("Crosses:",gCrosses(p1,l1),
    				"\nOverlaps:",gOverlaps(p1,l1)))

    	plot(p1,border='blue',col='blue');plot(p2,add=TRUE)
    	title(paste("Crosses:",gCrosses(p1,p2),
    				"\nOverlaps:",gOverlaps(p1,p2)))

[Package rgeos version 0.5-1 Index]