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.
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)
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:
Number of grid columns.
Number of grid rows.
x coordinate of the corner of the lower left grid cell.
y coordinate of the corner of the lower left grid cell.
Single numeric value specifying the size of a grid cell or pixel in both x and y direction.
Single numeric value being interpreted as NA (typically -9999.
x coordinate of the center of the lower left grid cell
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.
file name of an ASCII grid (extension defaults to .asc if not specified), or a connection open for reading or writing, as required
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.
numeric, specifying how detailed the output reporting the progress should be (currently 0 to 2, 0 being minimum output).
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.
logical: if TRUE, read the whole grid with one scan command; if FALSE, read it row by row using scan with option nlines=1.
passed on to scan().
read.sgrd, write.sgrd: additional arguments to be passed to rsaga.geoprocessor
file name of a grid stored as an R (.Rd) file; extension defaults to .Rd
integer: number of digits of temporary ASCII grid used for importing or exporting a SAGA grid
grid data: a data matrix, or a list with components data (the grid data matrix) and header (the grid header information).
optional list argument specifying the grid header information as returned by the read.ascii.grid or read.ascii.grid.header function; see Details
logical: should the header be written with the grid data? (default: TRUE)
numeric: if not missing, write data rounded to this many decimal places
numeric: see hdr.prec
character (default: "."): decimal mark used in input or output file
character: specifies whether the output grid should be georeferenced by the "center" or "corner" of its lower left grid cell; defaults to "corner".
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)
logical: should the .Rd file written by write.Rd.file be compressed? (default: TRUE)
Alexander Brenning
sf::read_sf() and sf::write_sf() in package sf, and readAsciiGrid and writeAsciiGrid in package maptools