maptools (version 0.8-39)

readShapeSpatial: Read shape files into Spatial*DataFrame objects

Description

The readShapeSpatial reads data from a shapefile into a Spatial*DataFrame object. The writeSpatialShape function writes data from a Spatial*DataFrame object to a shapefile. Note DBF file restrictions in write.dbf.

Usage

readShapeSpatial(fn, proj4string=CRS(as.character(NA)), verbose=FALSE, repair=FALSE, IDvar=NULL, force_ring=FALSE, delete_null_obj=FALSE, retrieve_ABS_null=FALSE) writeSpatialShape(x, fn, factor2char = TRUE, max_nchar=254)

Arguments

fn
shapefile layer name, when writing omitting the extensions *.shp, *.shx and *.dbf, which are added in the function
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.
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 (Polygons only)
force_ring
if TRUE, close unclosed input rings (Polygons only)
delete_null_obj
if TRUE, null geometries inserted by ABS will be removed together with their data.frame rows (Polygons and Lines)
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 (Polygons only)
x
a vector data Spatial*DataFrame 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

Value

a Spatial*DataFrame object of a class corresponding to the input shapefile

Details

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 row.names are added to the DBF file as column SP\_ID.

See Also

write.dbf

Examples

library(maptools)
xx <- readShapeSpatial(system.file("shapes/sids.shp", package="maptools")[1],
 IDvar="FIPSNO", proj4string=CRS("+proj=longlat +ellps=clrk66"))
summary(xx)
xxx <- xx[xx$SID74 < 2,]
tmpfl <- paste(tempdir(), "xxpoly", sep="/")
writeSpatialShape(xxx, tmpfl)
getinfo.shape(paste(tmpfl, ".shp", sep=""))
unlink(paste(tmpfl, ".*", sep=""))
xx <- readShapeSpatial(system.file("shapes/fylk-val.shp",
 package="maptools")[1], proj4string=CRS("+proj=utm +zone=33 +datum=WGS84"))
summary(xx)
xxx <- xx[xx$LENGTH > 30000,]
plot(xxx, col="red", add=TRUE)
tmpfl <- paste(tempdir(), "xxline", sep="/")
writeSpatialShape(xxx, tmpfl)
getinfo.shape(paste(tmpfl, ".shp", sep=""))
unlink(paste(tmpfl, ".*", sep=""))
xx <- readShapeSpatial(system.file("shapes/baltim.shp", package="maptools")[1])
summary(xx)
xxx <- xx[xx$PRICE < 40,]
tmpfl <- paste(tempdir(), "xxpts", sep="/")
writeSpatialShape(xxx, tmpfl)
getinfo.shape(paste(tmpfl, ".shp", sep=""))
unlink(paste(tmpfl, ".*", sep=""))