Extract levels from 4-dimensional NetCDF files.
This function extracts one or all levels of a 4-dimensional NetCDF file. A level is defined as a dimension, which does not correspond to longitude, latitude or time. The user can choose either one specific level (given by an integer) or all levels (level = "all").
extract.level( var, infile, outfile, level = 1, nc34 = 4, overwrite = FALSE, verbose = FALSE )
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). |
level |
Number of level (default = 1) or all levels (level = "all") (numeric or character). |
nc34 |
NetCDF version of output file. If |
overwrite |
logical; should existing output file be overwritten? |
verbose |
logical; if TRUE, progress messages are shown |
A NetCDF file including the selected level is written. In case of level = "all" all levels are written in separate NetCDF files and outfile names are expanded by "_level" and the level number.
Other selection and removal functions:
extract.period(),
sellonlatbox(),
selmon(),
selperiod(),
selpoint.multi(),
selpoint(),
seltime(),
selyear()
## 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)
height <- seq(0, 1000, 100)
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, 11, 132))
## create example NetCDF
x <- ncdim_def(name = "lon", units = "degrees_east", vals = lon)
y <- ncdim_def(name = "lat", units = "degrees_north", vals = lat)
z <- ncdim_def(name = "height", units = "m", vals = height)
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, z, 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")
ncatt_put(ncnew, "height", "standard_name", "height", prec = "text")
nc_close(ncnew)
## Extract the first level of the example CM SAF NetCDF file and write
## the output to a new file.
extract.level("SIS", file.path(tempdir(),"CMSAF_example_file.nc"),
file.path(tempdir(),"CMSAF_example_file_extract.level1.nc"))
## Extract all levels of the example CM SAF NetCDF file and write the
## output to a new file.
extract.level(var = "SIS", infile = file.path(tempdir(),"CMSAF_example_file.nc"),
outfile = file.path(tempdir(),"CMSAF_example_file_extract.level2.nc"),
level = "all")
unlink(c(file.path(tempdir(),"CMSAF_example_file.nc"),
file.path(tempdir(),"CMSAF_example_file_extract.level1.nc"),
file.path(tempdir(),"CMSAF_example_file_extract.level2_level[1-9].nc"),
file.path(tempdir(),"CMSAF_example_file_extract.level2_level10.nc"),
file.path(tempdir(),"CMSAF_example_file_extract.level2_level11.nc")))Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.