readShapeLines {maptools} | R Documentation

## Read arc shape files into SpatialLinesDataFrame objects

### Description

The `readShapeLines` function reads data from an arc/line shapefile into a `SpatialLinesDataFrame` object; the shapefile may be of type polygon, but for just plotting for example coastlines, a SpatialLines object is sufficient. The `writeLinesShape` function writes data from a `SpatialLinesDataFrame` object to a shapefile. Note DBF file restrictions in `write.dbf`.

### Usage

    readShapeLines(fn, proj4string=CRS(as.character(NA)), verbose=FALSE,
     repair=FALSE, delete_null_obj=FALSE)
    writeLinesShape(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.
`delete_null_obj` | if TRUE, null geometries will be removed together with their data.frame rows
`x` | a `SpatialLinesDataFrame` 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`

### Details

The shpID values of the shapefile will be used as `Lines` ID values; when writing shapefiles, the object data slot row.names are added to the DBF file as column SL\_ID.

### Value

a SpatialLinesDataFrame object

### Author(s)

Roger Bivand

### See Also

`write.dbf`

### Examples

    xx <- readShapeLines(system.file("shapes/fylk-val.shp", package="maptools")[1],
     proj4string=CRS("+proj=utm +zone=33 +datum=WGS84"))
    plot(xx, col="blue")
    summary(xx)
    xxx <- xx[xx$LENGTH > 30000,]
    plot(xxx, col="red", add=TRUE)
    tmpfl <- paste(tempdir(), "xxline", sep="/")
    writeLinesShape(xxx, tmpfl)
    getinfo.shape(paste(tmpfl, ".shp", sep=""))
    axx <- readShapeLines(tmpfl, proj4string=CRS("+proj=utm +zone=33 +datum=WGS84"))
    plot(xxx, col="black", lwd=4)
    plot(axx, col="yellow", lwd=1, add=TRUE)
    unlink(paste(tmpfl, ".*", sep=""))
    xx <- readShapeLines(system.file("shapes/sids.shp", package="maptools")[1],
     proj4string=CRS("+proj=longlat +datum=NAD27"))
    plot(xx, col="blue")

[Package maptools version 0.8-39 Index]