readVECT {rgrass}

Read and write GRASS vector object files

Description

read_VECT moves one GRASS vector object file with attribute data through a temporary GeoPackage file to a terra "SpatVector" object; write_VECT moves a terra "SpatVector" object through a temporary GeoPackage file 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.

Usage

read_VECT(vname, layer, type=NULL, flags="overwrite",
    ignore.stderr = NULL)
write_VECT(x, vname, flags="overwrite", ignore.stderr = NULL)
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 vector file name

layer

a layer name (string); if missing set to default of “1”

type

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

ignore.stderr

default the value set by set.ignore.stderrOption; 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

x

A "SpatVector" object moved to GRASS

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

read_VECT imports a GRASS vector object into a "SpatVector" 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.

Author(s)

Roger S. Bivand, e-mail: [e-mail]

Examples

run <- FALSE
if (nchar(Sys.getenv("GISRC")) > 0 &&
  read.dcf(Sys.getenv("GISRC"))[1,"LOCATION_NAME"] == "nc_basic_spm_grass7") run <- TRUE
GV <- Sys.getenv("GRASS_VERBOSE")
Sys.setenv("GRASS_VERBOSE"=0)
ois <- get.ignore.stderrOption()
set.ignore.stderrOption(TRUE)
if (run) {
  execGRASS("v.info", map="schools", layer="1")
}
if (run) {
  print(vInfo("schools"))
  schs <- read_VECT("schools")
  print(summary(schs))
}
if (run) {
  write_VECT(schs, "newsch", flags=c("o", "overwrite"))
  execGRASS("v.info", map="newsch", layer="1")
}
if (run) {
  nschs <- read_VECT("newsch")
  print(summary(nschs))
}
if (run) {
  print(all.equal(names(nschs), as.character(vColumns("newsch")[,2])))
}
if (run) {
  print(vInfo("roadsmajor"))
}
if (run) {
  roads <- read_VECT("roadsmajor")
  print(summary(roads))
}
if (run) {
  cen_neig <- vect2neigh("census")
  str(cen_neig)
}
if (run) {
  execGRASS("g.remove", flags="f", name=c("newsch", "newsch1"), type="vector")
}
Sys.setenv("GRASS_VERBOSE"=GV)
set.ignore.stderrOption(ois)