cmsaf (version 1.9.5)

remapbil: Bilinear grid interpolation.

Description

The function interpolates the data of infile1 to the grid of infile2. From infile2 only the grid information is used. Both grids have to be regular. For interpolation a simple bilinear interpolation is used as provided by the fields-package's interp.surface.grid function.

Usage

remapbil(var, infile1, infile2, outfile, nc34)

Arguments

var

Name of NetCDF variable in infile1 (character).

infile1

Filename of first input NetCDF file. This may include the directory (character). The data of infile1 are interpolated.

infile2

Filename of second input NetCDF file. This may include the directory (character). The grid information of infile2 are the target grid for the interpolation.

outfile

Filename of output NetCDF file. This may include the directory (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 interpolated data of infile1 on the grid of infile2 is written.

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)
  lon2 <- seq(5,15,1)
  lat2 <- seq(45,55,1)
  time <- c(as.Date('2000-01-01'), as.Date('2001-02-01'))
  origin <- as.Date('1983-01-01 00:00:00')
  time <- as.numeric(difftime(time,origin,units='hour'))
  data1 <- array(250:350,dim=c(21,21,1))
  data2 <- array(230:320,dim=c(21,21,1))

## create two example NetCDF files

   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[1],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_1.nc',vars)
   ncvar_put(ncnew,var1,data1)
   ncatt_put(ncnew,'lon','standard_name','longitude',prec='text')
   ncatt_put(ncnew,'lat','standard_name','latitude',prec='text')
   nc_close(ncnew)

   x <- ncdim_def(name='lon',units='degrees_east',vals=lon2)
   y <- ncdim_def(name='lat',units='degrees_north',vals=lat2)
   t <- ncdim_def(name='time',units='hours since 1983-01-01 00:00:00',
   vals=time[1],unlim=TRUE)
   ncnew <- nc_create('CMSAF_example_file_2.nc',vars)
   ncvar_put(ncnew,var1,data2)
   ncatt_put(ncnew,'lon','standard_name','longitude',prec='text')
   ncatt_put(ncnew,'lat','standard_name','latitude',prec='text')
   nc_close(ncnew)

## Interpolate the fields of both example CM SAF NetCDF file 1 to the 
## coarser grid of file 2 and write the result into one output file.
   remapbil('SIS','CMSAF_example_file_1.nc', 'CMSAF_example_file_2.nc', 
   'CMSAF_example_file_remapbil.nc')
# }