Read data from a netCDF file — nc_get

Read values of a given variable from a netCDF file or NetCDF object. If variable is 2D the data.frame has (x, y, t, value) columns. If variable is 3D the data.frame has (x, y, z, t, value) columns. Names of dimensions are preserved from input archive.

Usage

nc_get_variable(input = NULL, variable = NULL, tz = "UTC")

Arguments

input: Path to NetCDF single file, list of files or directory with NetCDF files. It can also be a single or a list of NetCDF objects read by RNetCDF::open.nc.
variable: character vector with the name of the variable to be read.
tz: optional character string with time zone (default = "UTC").

Value

A data.table with the value of required variable for each row.

Details

All netCDF functions in AirVeg are compatibile with the CF convention and IO/API data files (ex. CMAQ). We assume that data are on horizontally-regular grids.

According to NetCDF Climate and Forecast (CF) Metadata Conventions, if the time zone is omitted the default is UTC. In order to deal with special cases or with archives not compliant with CF convention, the optional timezone argument is provided to force it. timezone must be included in the Olson database. OlsonNames function (in the base package) provides a list of known locations.

Attention: in order to set UTC+1 (without automatic switching of DST) the ETC/GMT-1 string must be specified.

Examples

if (FALSE) {
concfile <- c("extdata/conc_farm.nc")
no2 <- nc_get_variable(input = concfile, variable = "c_NO2", tz = "Etc/GMT-1")
}