sellonlatbox {cmsafops}

Select a region by longitude and latitude.

Description

This function cuts a region from data of a CM SAF NetCDF file. The region is selected by giving the coordinates of the lower left and upper right corner of an rectangular grid area.

Usage

sellonlatbox(
  var,
  infile,
  outfile,
  lon1 = -180,
  lon2 = 180,
  lat1 = -90,
  lat2 = 90,
  nc34 = 4,
  overwrite = FALSE,
  verbose = FALSE,
  nc = NULL
)

Arguments

var

Name of NetCDF variable (character).

infile

Filename of input NetCDF file. This may include the directory (character).

outfile

Filename of output NetCDF file. This may include the directory (character).

lon1

Longitude of lower left corner (numeric).

lon2

Longitude of upper right left corner (numeric).

lat1

Latitude of lower left corner (numeric).

lat2

Latitude of upper right corner (numeric).

nc34

NetCDF version of output file. If nc34 = 3 the output file will be in NetCDFv3 format (numeric). Default output is NetCDFv4.

overwrite

logical; should existing output file be overwritten?

verbose

logical; if TRUE, progress messages are shown

nc

Alternatively to infile you can specify the input as an object of class ncdf4 (as returned from ncdf4::nc_open).

Value

A NetCDF file including the selected region is written.

See Also

Other selection and removal functions: extract.level(), extract.period(), selmon(), selperiod(), selpoint(), selpoint.multi(), seltime(), selyear()

Examples

## Create an example NetCDF file with a similar structure as used by CM
## SAF. The file is created with the ncdf4 package.  Alternatively
## example data can be freely downloaded here: <https://wui.cmsaf.eu/>

library(ncdf4)

## create some (non-realistic) example data

lon <- seq(5, 15, 0.5)
lat <- seq(45, 55, 0.5)
time <- seq(as.Date("2000-01-01"), as.Date("2010-12-31"), "month")
origin <- as.Date("1983-01-01 00:00:00")
time <- as.numeric(difftime(time, origin, units = "hour"))
data <- array(250:350, dim = c(21, 21, 132))

## create example NetCDF

x <- ncdim_def(name = "lon", units = "degrees_east", vals = lon)
y <- ncdim_def(name = "lat", units = "degrees_north", vals = lat)
t <- ncdim_def(name = "time", units = "hours since 1983-01-01 00:00:00",
 vals = time, unlim = TRUE)
var1 <- ncvar_def("SIS", "W m-2", list(x, y, t), -1, prec = "short")
vars <- list(var1)
ncnew <- nc_create(file.path(tempdir(),"CMSAF_example_file.nc"), vars)
ncvar_put(ncnew, var1, data)
ncatt_put(ncnew, "lon", "standard_name", "longitude", prec = "text")
ncatt_put(ncnew, "lat", "standard_name", "latitude", prec = "text")
nc_close(ncnew)

## Cut a region of the example CM SAF NetCDF file and write the output
## to a new file.
sellonlatbox(var = "SIS", infile = file.path(tempdir(),"CMSAF_example_file.nc"),
 outfile = file.path(tempdir(),"CMSAF_example_file_sellonlatbox.nc"), 
 lon1 = 8, lon2 = 12, lat1 = 48, lat2 = 52)

unlink(c(file.path(tempdir(),"CMSAF_example_file.nc"), 
 file.path(tempdir(),"CMSAF_example_file_sellonlatbox.nc")))