cmsafops: sellonlatbox – R documentation

Become an expert in R — Interactive courses, Cheat Sheets, certificates and more!

sellonlatbox

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
)

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

Value

A NetCDF file including the selected region is written.

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")))

cmsafops

Tools for CM SAF NetCDF Data

v1.1.1

GPL (>= 3)

Authors

Steffen Kothe [aut, cre]

Initial release