writeOGR with a spatialpolygon simplified by gSimplify

Question

I'm using gSimplify (rgeos package) to simplify the geometries of a shapefile. The funcion works good, but now I can't write the output in a new shapefile. I tried some ways:

writeOGR(simplyshape, file, driver="ESRI Shapefile", layer='test')

I get

obj must be a SpatialPointsDataFrame, SpatialLinesDataFrame or SpatialPolygonsDataFrame

and with:

writePolyShape(simplyshape, file)

I get:

Error: is(x, "SpatialPolygonsDataFrame") is not TRUE

Answer 1

Coerce your object to the appropriate Spatial*DataFrame-class (Points/Lines/Polygons), e.g. for SpatialPolygons using as(x, "SpatialPolygonsDataFrame" ):

R> l <- readWKT("LINESTRING(0 7,1 6,2 1,3 4,4 1,5 7,6 6,7 4,8 6,9 4)")
R> x1 <- gSimplify(p, tol=10)
R> class(x1)
[1] "SpatialPolygons"
attr(,"package")
[1] "sp"
R> x2 <- as(x, "SpatialPolygonsDataFrame")
R> class(x2)
[1] "SpatialPolygonsDataFrame"
attr(,"package")
[1] "sp"

Answer 2

You need to convert your SpatialPolygons class to a SpatialPolygonsDataFrame class. For example:

require(rgdal)
require(rgeos)

# Read shapefile
shp = 'C:/temp/myshp.shp'
myshp = readOGR(shp, layer = basename(strsplit(shp, "\\.")[[1]])[1])

# Read shapefile attributes
df = data.frame(myshp)

# Simplify geometry using rgeos
simplified = gSimplify(myshp, tol = 1000, topologyPreserve=FALSE)

# Create a spatial polygon data frame (includes shp attributes)
spdf = SpatialPolygonsDataFrame(simplified, df)

# Write to shapefile
writeOGR(spdf, layer = 'myshp_simplified', 'C:/temp', driver="ESRI Shapefile")