Extract data at a given point.
This function extracts all data at a given point. A point is given by a pair of longitude and latitude coordinates. The function will find the closest grid point to the given coordinates and extracts the data for this point. The output-file can be optional in NetCDF or csv. The outfile is checked for the correct file extension.
selpoint( var, infile, outfile, lon1 = 0, lat1 = 0, format = "nc", 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). |
lon1 |
Longitude of desired point (numeric). |
lat1 |
Latitude of desired point (numeric). |
format |
Intended output format. Options are |
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 or csv file including the selected point is written. The csv file is tested for use in Excel and includes two columns (Time and Data), which are separated by ';'.
Other selection and removal functions:
extract.level(),
extract.period(),
sellonlatbox(),
selmon(),
selperiod(),
selpoint.multi(),
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)
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(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")
nc_close(ncnew)
## Select a point of the example CM SAF NetCDF file and write the output
## to a csv-file.
selpoint(var = "SIS", infile = file.path(tempdir(),"CMSAF_example_file.nc"),
outfile = file.path(tempdir(),"CMSAF_example_file_selpoint.nc"),
lon1 = 8, lat1 = 48, format = "csv")
unlink(c(file.path(tempdir(),"CMSAF_example_file.nc"),
file.path(tempdir(),"CMSAF_example_file_selpoint.nc.csv")))Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.