spgrass6 (version 0.8-9)

readRAST: Read and write GRASS 6+ raster files

Description

Read GRASS 6+ raster files from GRASS 6+ into R SpatialGridDataFrame objects, and write single columns of R SpatialGridDataFrame objects to GRASS 6+. readRAST and writeRAST use temporary binary files and r.out.bin and r.in.bin rather than the temporary ASCII files used in earlier implementations. The earlier versions may still be used in a transition period. The functions readRAST and readRAST6 as well as writeRAST and writeRAST6 are identical and the functions ending with ...6 are maintained only for backward compatibility and might be deprecated.

Usage

readRAST(vname, cat=NULL, ignore.stderr = NULL, NODATA=NULL, plugin=NULL, mapset=NULL, useGDAL=NULL, close_OK=TRUE, drivername="GTiff", driverFileExt=NULL, return_SGDF=TRUE)
writeRAST(x, vname, zcol = 1, NODATA=NULL, ignore.stderr = NULL, useGDAL=NULL, overwrite=FALSE, flags=NULL, drivername="GTiff")

Arguments

vname

A vector of GRASS 6.0 raster file names

cat

default NULL; if not NULL, must be a logical vector matching vname, stating which (CELL) rasters to return as factor

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

plugin

default NULL does auto-detection, changes to FALSE if vname is longer than 1, and a sanity check will be run on raster and current region, and the function will revert to FALSE if mismatch is found; if TRUE, the plugin is available and the raster should be read in its original region and resolution; if the plugin is used, no further arguments other than mapset are respected

mapset

default NULL, if plugin is TRUE, the mapset of the file to be imported will be autodetected; if not NULL and if plugin is TRUE, a character string overriding the autodetected mapset, otherwise ignored

useGDAL

default NULL, taking the value set by set.useGDALOption; use r.out.gdal or plugin and readGDAL if autodetected or plugin=TRUE; or for writing writeGDAL, GTiff, and r.in.gdal, if FALSE using r.out.bin or r.in.bin

close_OK

default TRUE - clean up possible open connections used for reading metadata; may be set to FALSE to avoid the side-effect of other user-opened connections being broken

drivername

default "GTiff"; a valid GDAL writable driver name to define the file format for intermediate files

driverFileExt

default NULL; otherwise string value of required driver file name extension

return_SGDF

default TRUE returning a SpatialGridDataFrame object, if FALSE, return a list with a GridTopology object, a list of bands, and a proj4string; see example below

x

A SpatialGridDataFrame object for export to GRASS as a raster layer

zcol

Attribute column number or name

NODATA

by default NULL, in which case it is set to one less than floor()of the data values, otherwise an integer NODATA value (required to be integer by GRASS r.out.bin)

overwrite

default FALSE, if TRUE inserts "overwrite" into the value of the flags argument if not already there to allow existing GRASS rasters to be overwritten

flags

default NULL, character vector, for example "overwrite"

Value

readRAST returns a SpatialGridDataFrame objects with an data.frame in the data slots, and with the projection argument set. Note that the projection argument set is the the GRASS rendering of proj4, and will differ from the WKT/ESRI rendering returned by readVECT in form but not meaning. They are exchangeable but not textually identical, usually with the +ellps= term replaced by ellipsoid parameters verbatim. If return_SGDF is FALSE, a list with a GridTopology object, a list of bands, and a proj4string is returned, with an S3 class attribute of “gridList”.

Examples

if (nchar(Sys.getenv("GISRC")) > 0) {
  require(rgdal)
  ois <- get.ignore.stderrOption()
  set.ignore.stderrOption(TRUE)
  get.useGDALOption()
  spear <- readRAST(c("geology", "elevation.dem"), cat=c(TRUE, FALSE),
    useGDAL=FALSE)
  spear <- readRAST(c("geology", "elevation.dem"), cat=c(TRUE, FALSE),
    useGDAL=TRUE)
  print(table(spear$geology))
  execGRASS("r.stats", flags=c("c", "l", "quiet"), input="geology")
  boxplot(spear$elevation.dem ~ spear$geology)
  spear$sqdem <- sqrt(spear$elevation.dem)
  if ("GRASS" %in% gdalDrivers()$name) {
    execGRASS("g.region", rast="elevation.dem")
    dem1 <- readRAST("elevation.dem", plugin=TRUE, mapset="PERMANENT")
    print(summary(dem1))
    execGRASS("g.region", rast="elevation.dem")
  }
  writeRAST(spear, "sqdemSP", zcol="sqdem")
  execGRASS("r.info", map="sqdemSP")
  execGRASS("g.remove", rast="sqdemSP")
  writeRAST(spear, "sqdemSP", zcol="sqdem", useGDAL=TRUE)
  execGRASS("r.info", map="sqdemSP")
  print(system.time(sqdemSP <- readRAST(c("sqdemSP", "elevation.dem"),
    useGDAL=TRUE, return_SGDF=FALSE)))
  print(system.time(sqdemSP <- readRAST(c("sqdemSP", "elevation.dem"),
    useGDAL=TRUE, return_SGDF=TRUE)))
  print(system.time(sqdemSP <- readRAST(c("sqdemSP", "elevation.dem"),
    useGDAL=FALSE, return_SGDF=TRUE)))
  print(system.time(sqdemSP <- readRAST(c("sqdemSP", "elevation.dem"),
    useGDAL=FALSE, return_SGDF=FALSE)))
  str(sqdemSP)
  mat <- do.call("cbind", sqdemSP$dataList)
  str(mat)
  print(system.time(SGDF <- SpatialGridDataFrame(grid=sqdemSP$grid,
    proj4string=sqdemSP$proj4string, data=as.data.frame(sqdemSP$dataList))))
  summary(SGDF)
  execGRASS("g.remove", rast="sqdemSP")
  if (execGRASS("g.version", intern=TRUE) > "GRASS 7") {
    execGRASS("r.mapcalc", expression="quads0 = quads - 1")
  } else {
    execGRASS("r.mapcalculator", outfile="quads0",
      amap="quads", formula='A - 1')
  }
  execGRASS("r.stats", flags="c", input="quads0")
  quads0 <- readRAST("quads0")
  print(table(quads0$quads0))
  quads0 <- readRAST("quads0", plugin=FALSE)
  print(table(quads0$quads0))
  execGRASS("g.remove", rast="quads0")
  set.ignore.stderrOption(ois)
}