remap {cmsafops}

Grid interpolation.

Description

The function interpolates the data of infile1 to the grid of infile2. From infile2 only the grid information is used. By default, a nearest neighbor interpolation provided by get.knnx is used. For interpolation between regular grids a simple bilinear interpolation as provided by interp.surface.grid as well as a conservative remapping as provided by remapcon can be chosen.

Usage

remap(
  var,
  infile1,
  infile2,
  outfile,
  method = "nearest",
  dxy_factor = 1,
  nc34 = 4,
  overwrite = FALSE,
  verbose = FALSE,
  nc1 = NULL,
  nc2 = NULL
)

Arguments

var

Name of NetCDF variable (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 file. This may include the directory (character). The grid information of infile2 are the target grid for the interpolation. This File may also be an ASCII-File containing the grid information.

outfile

Filename of output NetCDF file. This may include the directory (character).

method

Method used for remapping (character). Options are "bilinear" for bilinear interpolation, "conservative" for conservative remapping (only for regular grids, respectively) and "nearest" for nearest-neighbor interpolation. Default is "nearest".

dxy_factor

In case of nearest neighbor all grid points with distance > (dxy * dxy_factor) are set to NA (numeric). Default is 1.

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

nc1

Alternatively to infile1 you can specify the input as an object of class ncdf4 (as returned from ncdf4::nc_open).

nc2

Alternatively to infile2 you can specify the input as an object of class ncdf4 (as returned from ncdf4::nc_open).

Value

A NetCDF file including the interpolated data of infile1 on the grid of infile2 is written.

See Also

Other data manipulation functions: acsaf_box_mergetime(), add_grid_info(), box_mergetime(), cmsaf.transform.coordinate.system(), levbox_mergetime(), map_regular()

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)
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(file.path(tempdir(),"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(file.path(tempdir(),"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.
remap(var = "SIS", infile1 = file.path(tempdir(),"CMSAF_example_file_1.nc"), 
 infile2 = file.path(tempdir(),"CMSAF_example_file_2.nc"),
 outfile = file.path(tempdir(),"CMSAF_example_file_remap.nc"))

unlink(c(file.path(tempdir(),"CMSAF_example_file_1.nc"), 
 file.path(tempdir(),"CMSAF_example_file_2.nc"),
 file.path(tempdir(),"CMSAF_example_file_remap.nc")))