cmsaf (version 1.9.5)

selpoint.multi: Extract data at multiple points.

Description

This function extracts all data at given points. The points are given by a pair of vectors with longitude and latitude coordinates. The function will find the closest grid points to the given coordinates and extracts the data for these points. For each point a separate output file is written. The output-files can be optional in NetCDF or csv. Input can be a single NetCDF file (given by the infile attribute) or a bunch of NetCDF files (given by the path and pattern attributes).

Usage

selpoint.multi(var,infile,path,pattern,outpath,lon1,lat1,station_names,format,nc34)

Arguments

var

Name of NetCDF variable (character).

infile

Filename of input NetCDF file. This may include the directory (character). Infile is not needed if path and pattern are given.

path

Directory of input files (character). Will not be used if infile is given.

pattern

Pattern that all desired files in the 'path' directory have in common (character).

outpath

Directory were output files will be stored (character).

lon1

Longitude vector of desired points (numeric vector). lon1 must have the same length as lat1.

lat1

Latitude vector of desired points (numeric vector). lat1 must have the same length as lon1.

station_names

Optional vector of names, which will be used for the output files (character vector). station_names must have the same length as lon1 and lat1.

format

Intended output format. Options are 'nc' or 'csv'. Default is 'nc' (character).

nc34

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

Value

For each pair of longitude and latitude coordinates one separate NetCDF or csv file including the selected data is written. The csv-files are tested for use in Excel and include four coloumns (Time ; Data ; Longitude ; Latitude), which are seperated by ';'. If station_names are defined, the output files will be named according to this vector. Otherwise, the output files will be named as selpoint_longitude_latitude.format. Already existing files will be overwritten in case that station_names are given or renamed (e.g., selpoint1_longitude_latitude.nc) in case that no station_names are given.

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)
  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('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)

## Select two points of the example CM SAF NetCDF file and write the output 
## to a csv-file.
   selpoint.multi(var='SIS',infile='CMSAF_example_file.nc', 
   outpath=getwd(),lon1=c(8,9),lat1=c(48,49),station_names=c("A","B"),format='csv')
# }