Get Indices to Use When Clipping netcdf Files at Import

This function works out how much of a netcdf file to read, to capture the data between a given Lat-Lon window.

Usage

Window(file, w = NULL, e = NULL, s = NULL, n = NULL, shift = FALSE, sf = NULL)

Arguments

file

The full name of a netcdf file containing a longitude and latitude dimension.

w

Degrees West to read from.

e

Degrees East to read to.

s

Degrees South to read from.

n

Degrees North to read to.

shift

True/False does the file use 0-360 longitudes? If yes, negative longitudes are corrected.

sf

An sf polygon can be supplied instead of `w`,`e`,`s`, and `n`. The function takes these values from the bounding box.

Value

A list of three elements:

• Lats - A vector of latitudes from `s` to `n`.

• Lons - A vector of longitudes from `w` to `e`.

• Limits - A dataframe containing the index to start reading from (Lon_start, Lat_start) and the length of the vector to read (Lon_count, Lat_count.

Details

The function reads in a vector for both latitudes and longitudes, and tests whether each entry is within the specified window. The max and min position in these vectors where the condition == TRUE are taken to define the ends of the window to import. The vectors of latitudes and longitudes between these limits are kept, so they can be added to the variables of interest during extraction.

See also

Other NEMO-MEDUSA spatial tools: Update-drivers, sfc_as_cols(), vectors_2_direction()