Simplify Geometry

Function simplifies the given geometry using the Douglas-Peuker algorithm

gSimplify(spgeom, tol, topologyPreserve=FALSE)

Arguments

spgeom

sp object as defined in package sp

tol

Numerical tolerance value to be used by the Douglas-Peuker algorithm

topologyPreserve

Logical determining if the algorithm should attempt to preserve the topology of the original geometry

Value

Returns a simplified version of the given geometry when applied to [MULTI]LINEs or [MULTI]POLYGONs.

Details

When applied to lines it is possible for the resulting geometry to lose simplicity (gIsSimple). If topologyPreserve is not specified it is also possible that the resulting geometries may no longer be valid (gIsValid). Remember to check the resulting geometry as many other functions rely on simplicity and or validity when performing their calculations.

Author

Roger Bivand & Colin Rundel

Examples

p = readWKT(paste("POLYGON((0 40,10 50,0 60,40 60,40 100,50 90,60 100,60",
 "60,100 60,90 50,100 40,60 40,60 0,50 10,40 0,40 40,0 40))"))
l = readWKT("LINESTRING(0 7,1 6,2 1,3 4,4 1,5 7,6 6,7 4,8 6,9 4)")

par(mfrow=c(2,4))
plot(p);title("Original")
plot(gSimplify(p,tol=10));title("tol: 10")
plot(gSimplify(p,tol=20));title("tol: 20")
plot(gSimplify(p,tol=25));title("tol: 25")

plot(l);title("Original")
plot(gSimplify(l,tol=3));title("tol: 3")
plot(gSimplify(l,tol=5));title("tol: 5")
plot(gSimplify(l,tol=7));title("tol: 7")

par(mfrow=c(1,1))