readShapePoly {maptools} | R Documentation |
The readShapePoly
reads data from a polygon shapefile into a SpatialPolygonsDataFrame
object. The writePolyShape
function writes data from a SpatialPolygonsDataFrame
object to a shapefile.
readShapePoly(fn, IDvar=NULL, proj4string=CRS(as.character(NA)), verbose=FALSE, repair=FALSE, force_ring=FALSE, delete_null_obj=FALSE, retrieve_ABS_null=FALSE) writePolyShape(x, fn, factor2char = TRUE, max_nchar=254)
fn |
shapefile layer name, when writing omitting the extensions *.shp, *.shx and *.dbf, which are added in the function |
IDvar |
a character string: the name of a column in the shapefile DBF containing the ID values of the shapes - the values will be converted to a character vector |
proj4string |
Object of class CRS ; holding a valid proj4 string |
verbose |
default TRUE - report type of shapefile and number of shapes |
repair |
default FALSE: some shapefiles provided by Geolytics Inc. have values of object sizes stored in the *.shx index file that are eight bytes too large, leading the function to try to read past the end of file. If repair=TRUE, an attempt is made to repair the internal values, permitting such files to be read. |
force_ring |
if TRUE, close unclosed input rings |
delete_null_obj |
if TRUE, null geometries inserted by ABS will be removed together with their data.frame rows |
retrieve_ABS_null |
default FALSE, if TRUE and delete_null_obj also TRUE, the function will return a data frame containing the data from any null geometries inserted by ABS |
x |
a SpatialPolygonsDataFrame object |
factor2char |
logical, default TRUE, convert factor columns to character |
max_nchar |
default 254, may be set to a higher limit and passed through to the DBF writer, please see Details in write.dbf |
If no IDvar argument is given, the shpID values of the shapefile will be used as Polygons
ID values; when writing shapefiles, the object data slot rownames are added to the DBF file as column SP_ID.
a SpatialPolygonsDataFrame object
Roger Bivand
library(maptools) xx <- readShapePoly(system.file("shapes/sids.shp", package="maptools")[1], IDvar="FIPSNO", proj4string=CRS("+proj=longlat +ellps=clrk66")) plot(xx, border="blue", axes=TRUE, las=1) text(coordinates(xx), labels=sapply(slot(xx, "polygons"), function(i) slot(i, "ID")), cex=0.6) as(xx, "data.frame")[1:5, 1:6] xxx <- xx[xx$SID74 < 2,] plot(xxx, border="red", add=TRUE) tmpfl <- paste(tempdir(), "xxpoly", sep="/") writePolyShape(xxx, tmpfl) getinfo.shape(paste(tmpfl, ".shp", sep="")) axx <- readShapePoly(tmpfl, proj4string=CRS("+proj=longlat +ellps=clrk66")) plot(xxx, border="black", lwd=4) plot(axx, border="yellow", lwd=1, add=TRUE) unlink(paste(tmpfl, ".*", sep=""))