sellonlatbox: Select a region by longitude and latitude.

In cmsafops: Tools for CM SAF NetCDF Data

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.multi(), selpoint(), 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")))

cmsafops documentation built on Sept. 18, 2023, 5:16 p.m.