maptools (version 0.8-39)

thinnedSpatialPoly: Douglas-Peuker line generalization for Spatial Polygons

Description

The function applies the implementation of the Douglas-Peuker algorithm for line generalization or simplification (originally from shapefiles) to objects inheriting from Spatial Polygons. It does not preserve topology, so is suitable for visualisation, but not for the subsequent analysis of the polygon boundaries, as artefacts may be created, and boundaries of neighbouring entities may be generalized differently. If the rgeos package is available, thinnedSpatialPolyGEOS will be used with partial topology preservation instead of the R implementation here by passing arguments through.

Usage

thinnedSpatialPoly(SP, tolerance, minarea=0, topologyPreserve = FALSE, avoidGEOS = FALSE)

Arguments

SP
an object inheriting from the SpatialPolygons class
tolerance
the tolerance value in the metric of the input object
minarea
the smallest area of Polygon objects to be retained, ignored if rgeos used
topologyPreserve
choose between two rgeos options: logical determining if the algorithm should attempt to preserve the topology (nodes not complete edges) of the original geometry
avoidGEOS
use R DP code even if rgeos is available

Value

References

Douglas, D. and Peucker, T. (1973). Algorithms for the reduction of the number of points required to represent a digitized line or its caricature. The Canadian Cartographer 10(2). 112-122.

Examples

Run this code
xx <- readShapeSpatial(system.file("shapes/sids.shp", package="maptools")[1],
      IDvar="FIPSNO", proj4string=CRS("+proj=longlat +ellps=clrk66"))
object.size(as(xx, "SpatialPolygons"))
xxx <- thinnedSpatialPoly(xx, tolerance=0.05, minarea=0.001)
object.size(as(xxx, "SpatialPolygons"))
par(mfrow=c(2,1))
plot(xx)
plot(xxx)
par(mfrow=c(1,1))

Run the code above in your browser using DataCamp Workspace