spgrass6 (version 0.8-9)

readVECT6: Read and write GRASS 6+ vector object files

Description

readVECT moves one GRASS 6+ vector object file with attribute data through a temporary shapefile to a Spatial*DataFrame object of type determined by the GRASS 6+ vector object; writeVECT moves a Spatial*DataFrame object through a temporary shapefile to a GRASS vector object file. vect2neigh returns neighbour pairs with shared boundary length as described by Markus Neteler, in https://stat.ethz.ch/pipermail/r-sig-geo/2005-October/000616.html. cygwin_clean_temp can be called to try to clean the GRASS mapset-specific temporary directory under cygwin. The functions readVECT and readVECT6 as well as writeVECT and writeVECT6 are identical and the functions ending with ...6 are maintained only for backward compatibility and might be deprecated.

Usage

readVECT(vname, layer, type=NULL, plugin=NULL, remove.duplicates = TRUE, ignore.stderr = NULL, with_prj=TRUE, with_c=FALSE, mapset=NULL, pointDropZ=FALSE, driver="ESRI Shapefile")
writeVECT(SDF, vname,  v.in.ogr_flags=NULL, ignore.stderr = NULL, driver="ESRI Shapefile")
vInfo(vname, layer, ignore.stderr = NULL)
vColumns(vname, layer, ignore.stderr = NULL)
vDataCount(vname, layer, ignore.stderr = NULL)
vect2neigh(vname, ID=NULL, ignore.stderr = NULL, remove=TRUE, vname2=NULL, units="k")

Arguments

vname

A GRASS 6+ vector file name

layer

a layer name (integer in GRASS 6, string in GRASS 7); if missing set to default of 1

type

override type detection when multiple types are non-zero, passed to v.out.ogr

plugin

default NULL for auto-detection, may be set to FALSE to avoid or TRUE if the plugin is known to be available; if the plugin is used, no further arguments other than mapset are respected

remove.duplicates

In line and area vector objects, multiple geometrical features may be associated with a single cat number, leading to duplication of data rows; this argument attempts to combine the geometrical features so that they match a single data row

ignore.stderr

default NULL, taking the value set by set.ignore.stderrOption, can be set to TRUE to silence system() output to standard error; does not apply on Windows platforms

with_prj

default TRUE, write ESRI-style PRJ file for transfered data

with_c

default TRUE in GRASS 6, FALSE in GRASS 7; if TRUE in GRASS 6 or FALSE in GRASS 7, export features with category (labeled) only; if not default, all features are exported, including GRASS “islands” which are probably spurious exterior rings filling holes.

mapset

if plugin is TRUE, the mapset of the file to be imported may be changed from the current mapset by passing a character string

pointDropZ

default FALSE, if TRUE, discard third coordinates for point geometries; third coordinates are alway discarded for line and polygon geometries

driver

default "ESRI Shapefile"; a valid OGR writable driver name to define the file format for intermediate files, one of c("GML", "SQLite"), c("ESRI_Shapefile", "MapInfo_File")

SDF

A Spatial*DataFrame to be moved to GRASS6 as a vector object, for SpatialPointsDataFrame, SpatialLinesDataFrame, and SpatialPolygonsDataFrame objects

v.in.ogr_flags

Character vector containing additional optional flags and/or options for v.in.ogr, particularly "o" and "overwrite"

ID

A valid DB column name for unique identifiers (optional)

remove

default TRUE, remove copied vectors created in vect2neigh

vname2

If on a previous run, remove was FALSE, the name of the temporary vector may be given to circumvent its generation

units

default “k”; see GRASS v.to.db manual page for alternatives

Value

readVECT imports a GRASS6+ vector object into a Spatial*DataFrame object with the type determined by the type of the GRASS6 vector object; vect2neigh returns a data frame object with left and right neighbours and boundary lengths, also given class GRASSneigh and spatial.neighbour (as used in spdep). The incantation to retrieve the neighbours list is sn2listw(vect2neigh())$neighbours, and to retrieve the boundary lengths: sn2listw(vect2neigh())$weights. The GRASSneigh object has two other useful attributes: external is a vector giving the length of shared boundary between each polygon and the external area, and total giving each polygon's total boundary length.Note that GRASS6 vectors should be rebuilt by running “v.build.all” in each mapset.

Examples

if (nchar(Sys.getenv("GISRC")) > 0) {
  require(rgdal)
  ois <- get.ignore.stderrOption()
  set.ignore.stderrOption(TRUE)
  if (execGRASS("g.version", intern=TRUE) > "GRASS 7") {
    execGRASS("v.info", map="bugsites", layer="1")
  } else {
    execGRASS("v.info", map="bugsites", layer=1L)
  }
  print(vInfo("bugsites"))
  bugs <- readVECT("bugsites", plugin=NULL)
  print(summary(bugs))
  bugs1 <- readVECT("bugsites", plugin=FALSE)
  print(summary(bugs1))
  writeVECT(bugs, "newbugs", v.in.ogr_flags=c("o", "overwrite"))
  if (execGRASS("g.version", intern=TRUE) > "GRASS 7") {
    execGRASS("v.info", map="newbugs", layer="1")
  } else {
    execGRASS("v.info", map="newbugs", layer=1L)
  }
  nbugs <- readVECT("newbugs")
  print(summary(nbugs))
  print(vInfo("roads"))
  roads <- readVECT("roads")
  print(summary(roads))
  set.ignore.stderrOption(ois)
}