cmsaf (version 1.9.5)

extract.level: Extract levels from 4-dimensional NetCDF files.

Description

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").

Usage

extract.level(var, infile, outfile, level, nc34)

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).

level

Number of level (default = 1) or all levels (level = "all") (numeric or character).

nc34

NetCDF version of output file. If nc34=4 the output file will be in NetCDFv4 format (numeric). Default output is NetCDFv3.

Value

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.

Examples

# NOT RUN {
## 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('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','CMSAF_example_file.nc', 
   'CMSAF_example_file_extract.level.nc')
## Extract all levels of the example CM SAF NetCDF file and write 
## the output to a new file.
   extract.level('SIS','CMSAF_example_file.nc', 
   'CMSAF_example_file_extract.level.nc',"all")
# }