rotpole_nc_point_to_dt: Extract time series of a single grid cell of a rot-pole daily...

In eurocordexr: Makes it Easier to Work with Daily 'netCDF' from EURO-CORDEX RCMs

Extract time series of a single grid cell of a rot-pole daily netcdf to data.table

Description

Creates a data.table from a rotated pole netcdf (as usually found in RCMs), which includes values and date. Useful for extracting e.g. the series for a station. Requires that dimension variables in netcdf file contain rlon and rlat, and that it contains daily data.

Usage

rotpole_nc_point_to_dt(
  filename,
  variable,
  point_lon,
  point_lat,
  interpolate_to_standard_calendar = FALSE,
  verbose = FALSE,
  add_grid_coord = FALSE
)

Arguments

filename	Complete path to .nc file.
variable	Name of the variable to extract from filename (character).
point_lon	Numeric longitude of the point to extract (decimal degrees).
point_lat	Numeric latitude of the point to extract (decimal degrees).
interpolate_to_standard_calendar	Boolean, if TRUE will use map_non_standard_calendar to interpolate values to a standard calendar.
verbose	Boolean, if TRUE, will print more information.
add_grid_coord	Boolean, if TRUE, will add columns to the result which give the longitude and latitude of the underlying grid.

Details

Calculates the euclidean distance, and takes the grid cell with minimal distance to point_lon and point_lat. Requires that the .nc file contains variables lon[rlon, rlat] and lat[rlon, rlat].

Value

A data.table with two columns: the dates in date, and the values in a variable named after input variable. The date column is of class Date, unless the .nc file has a non-standard calendar (360, noleap) and interpolate_to_standard_calendar is set to FALSE, in which it will be character. If add_grid_coord is set to TRUE, then two more columns named grid_lon and grid_lat.

Examples

# example data from EURO-CORDEX (cropped for size)

# standard calendar
fn1 <- system.file("extdata", "test1.nc", package = "eurocordexr")
dt1 <- rotpole_nc_point_to_dt(
  filename = fn1,
  variable = "tasmin",
  point_lon = 11.31,
  point_lat = 46.5,
  verbose = TRUE
)

# non-standard calendar (360)
fn2 <- system.file("extdata", "test2.nc", package = "eurocordexr")

# read as is
dt2 <- rotpole_nc_point_to_dt(fn2, "tasmin", 11.31, 46.5)
str(dt2) # chr date
dt2[86:94, ] # e.g. 30th of February in 360 calendar

# interpolate to standard
dt3 <- rotpole_nc_point_to_dt(fn2, "tasmin", 11.31, 46.5,
                              interpolate_to_standard_calendar = TRUE)
str(dt3) # class Date
dt3[86:94, ] # standard calender

eurocordexr documentation built on Aug. 24, 2023, 9:07 a.m.