read.ascii.grid: Read/write ASCII, SAGA and Rd Grid Files

In RSAGA: SAGA Geoprocessing and Terrain Analysis

Read/write ASCII, SAGA and Rd Grid Files

Description

These functions provide simple interfaces for reading and writing grids from/to ASCII grids and Rd files. Grids are stored as matrices, their headers in lists.

Usage

read.ascii.grid(
  file,
  return.header = TRUE,
  print = 0,
  nodata.values = c(),
  at.once = TRUE,
  na.strings = "NA"
)

read.ascii.grid.header(file, ...)

read.sgrd(
  fname,
  return.header = TRUE,
  print = 0,
  nodata.values = c(),
  at.once = TRUE,
  prec = 7,
  ...
)

read.Rd.grid(fname, return.header = TRUE)

write.ascii.grid(
  data,
  file,
  header = NULL,
  write.header = TRUE,
  digits,
  hdr.digits = 10,
  dec = ".",
  georef = "corner"
)

write.ascii.grid.header(file, header, georef, dec = ".", hdr.digits = 10)

write.sgrd(
  data,
  file,
  header = NULL,
  prec = 7,
  hdr.prec = 10,
  georef = "corner",
  ...
)

write.Rd.grid(data, file, header = NULL, write.header = TRUE, compress = TRUE)

Arguments

file	file name of an ASCII grid (extension defaults to .asc if not specified), or a connection open for reading or writing, as required
return.header	logical: should the grid header be returned (default), or just the grid data matrix? In the former case, read.ascii.grid returns a list with two components named data and header.
print	numeric, specifying how detailed the output reporting the progress should be (currently 0 to 2, 0 being minimum output).
nodata.values	optional numeric vector specifying nodata values to be used in addition to the nodata value specified in the grid header; nodata values are converted to NA.
at.once	logical: if TRUE, read the whole grid with one scan command; if FALSE, read it row by row using scan with option nlines=1.
na.strings	passed on to scan().
...	read.sgrd, write.sgrd: additional arguments to be passed to rsaga.geoprocessor
fname	file name of a grid stored as an R (.Rd) file; extension defaults to .Rd
prec	integer: number of digits of temporary ASCII grid used for importing or exporting a SAGA grid
data	grid data: a data matrix, or a list with components data (the grid data matrix) and header (the grid header information).
header	optional list argument specifying the grid header information as returned by the read.ascii.grid or read.ascii.grid.header function; see Details
write.header	logical: should the header be written with the grid data? (default: TRUE)
digits	numeric: if not missing, write data rounded to this many decimal places
hdr.digits	numeric: see hdr.prec
dec	character (default: "."): decimal mark used in input or output file
georef	character: specifies whether the output grid should be georeferenced by the "center" or "corner" of its lower left grid cell; defaults to "corner".
hdr.prec	numeric: write (non-integer) header data with this many decimal places; a value of 9 or higher is recommended for compatibility with SAGA GIS (default: 10)
compress	logical: should the .Rd file written by write.Rd.file be compressed? (default: TRUE)

Value

The read.* functions return either a list with components data (the grid data matrix) and header (the grid header information, see below), if return.header=TRUE, or otherwise just the grid data matrix return.header=FALSE.

The grid data matrix is a numeric matrix whose first column corrensponds to the first (i.e. northernmost) row of the grid. Columns run from left = West to right = East.

The header information returned by the read.ascii.grid[.header] functions (if return.header=TRUE) is a list with the following components:

ncols	Number of grid columns.
nrows	Number of grid rows.
xllcorner	x coordinate of the corner of the lower left grid cell.
yllcorner	y coordinate of the corner of the lower left grid cell.
cellsize	Single numeric value specifying the size of a grid cell or pixel in both x and y direction.
nodata_value	Single numeric value being interpreted as NA (typically -9999.
xllcenter	x coordinate of the center of the lower left grid cell
yllcenter	y coordinate of the center of the lower left grid cell

Note: The order of the components, especially of ?llcorner and ?llcenter, may change, depending on the order in which they appear in the grid header and on the georeferencing method (center or corner) used for the grid. The ?llcorner and ?llcenter attributes differ only by cellsize/2.

Note

read.sgrd and write.sgrd import/export grids indirectly by creating temporary ASCII grid files (this explains why write.sgrd has prec and hdr.prec arguments). Consider using sf::read_sf() in package sf instead, which is likely more efficient but may require coercion of your gridded data to/from an object supported by sf.

The read.Rd.grid and write.Rd.grid functions use the load and save commands to store a grid. The variable name used is data, which is either a numeric matrix or a list with components data (the grid data matrix) and header (the grid header information).

Author(s)

Alexander Brenning

See Also

sf::read_sf() and sf::write_sf() in package sf, and readAsciiGrid and writeAsciiGrid in package maptools

RSAGA documentation built on Dec. 10, 2022, 1:12 a.m.