readShapePoly            package:maptools            R Documentation

_R_e_a_d _p_o_l_y_g_o_n _s_h_a_p_e _f_i_l_e_s _i_n_t_o _S_p_a_t_i_a_l_P_o_l_y_g_o_n_s_D_a_t_a_F_r_a_m_e _o_b_j_e_c_t_s

_D_e_s_c_r_i_p_t_i_o_n:

     The 'readShapePoly' reads data from a polygon shapefile into a
     'SpatialPolygonsDataFrame' object. The 'writePolyShape' function
     writes data from a 'SpatialPolygonsDataFrame' object to a
     shapefile.

_U_s_a_g_e:

     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)

_A_r_g_u_m_e_n_t_s:

      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'

_D_e_t_a_i_l_s:

     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.

_V_a_l_u_e:

     a SpatialPolygonsDataFrame object

_A_u_t_h_o_r(_s):

     Roger Bivand

_E_x_a_m_p_l_e_s:

     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=""))

