Is Geometry Simple?

Function tests if the given geometry is simple

gIsSimple(spgeom, byid = FALSE)

Arguments

spgeom

sp object as defined in package sp

byid

Logical determining if the function should be applied across subgeometries (TRUE) or the entire object (FALSE)

Value

Returns TRUE if the given geometry does not contain anomalous points, such as self intersection or self tangency.

Details

Simplicity is used in reference to 0 and 1-dimensional geometries ([MULTI]POINT and [MULTI]LINESTRING) whereas Validity (gIsValid) is used in reference to 2-dimensional geometries ([MULTI]POLYGON).

A POINT is always simple.

A MULTIPOINT is simple if no two points are identical.

A LINESTRING is simple if it does not pass through the same point twice (self intersection) except at the end points, in which case it is a ring (gIsRing).

A MULTILINESTRING is simple if all of its subgeometries are simple and none of the subgeometries intersect except at end points.

A [MULTI]POLYGON is simple by definition.

Many of the functions in rgeos expect simple/valid geometries and may exhibit unpredictable behavior if given an invalid geometry. Checking of validity/simplicity can be computationally expensive for complex geometries and so is not done by default, any new geometries should be checked.

Author

Roger Bivand & Colin Rundel

Examples

# MULTIPOINT examples
gIsSimple(readWKT("MULTIPOINT(1 1,2 2,3 3)"))
#> [1] TRUE
gIsSimple(readWKT("MULTIPOINT(1 1,2 2,1 1)"))
#> [1] FALSE

# LINESTRING examples
l1 = readWKT("LINESTRING(0 5,3 4,2 3,5 2)")
l2 = readWKT("LINESTRING(0 5,4 2,5 4,0 1)")
l3 = readWKT("LINESTRING(3 5,0 4,0 2,2 0,5 1,4 4,4 5,3 5)")
l4 = readWKT("LINESTRING(3 5,0 4,4 3,5 2,3 0,1 2,4 5,3 5)")

par(mfrow=c(2,2))
plot(l1);title(paste("Simple:",gIsSimple(l1)))
plot(l2);title(paste("Simple:",gIsSimple(l2)))
plot(l3);title(paste("Simple:",gIsSimple(l3)))
plot(l4);title(paste("Simple:",gIsSimple(l4)))


# MULTILINESTRING examples
ml1 = readWKT("MULTILINESTRING((0 5,1 2,5 0),(3 5,5 4,4 1))")
ml2 = readWKT("MULTILINESTRING((0 5,1 2,5 0),(0 5,5 4,4 1))")
ml3 = readWKT("MULTILINESTRING((0 5,1 2,5 0),(3 5,5 4,2 0))")

par(mfrow=c(1,3))
plot(ml1);title(paste("Simple:",gIsSimple(ml1)))
plot(ml2);title(paste("Simple:",gIsSimple(ml2)))
plot(ml3);title(paste("Simple:",gIsSimple(ml3)))