CFTime

CFTime encodes and decodes time units conforming to the Climate and Forecasting (CF) netCDF conventions. CFTime was split out of the NCDatasets julia package.

Installation

Inside the Julia shell, you can download and install the package by issuing:

using Pkg
Pkg.add("CFTime")

Example

using CFTime, Dates

# standard calendar

dt = CFTime.timedecode([0,1,2,3],"days since 2000-01-01 00:00:00")
# 4-element Array{Dates.DateTime,1}:
#  2000-01-01T00:00:00
#  2000-01-02T00:00:00
#  2000-01-03T00:00:00
#  2000-01-04T00:00:00


CFTime.timeencode(dt,"days since 2000-01-01 00:00:00")
# 4-element Array{Float64,1}:
#  0.0
#  1.0
#  2.0
#  3.0

# "360 day" calendar

dt = CFTime.timedecode([0,1,2,3],"days since 2000-01-01 00:00:00",DateTime360Day)
# 4-element Array of DateTime360Day
#  DateTime360Day(2000-01-01T00:00:00)
#  DateTime360Day(2000-01-02T00:00:00)
#  DateTime360Day(2000-01-03T00:00:00)
#  DateTime360Day(2000-01-04T00:00:00)

dt[2]-dt[1]
# 86400000 milliseconds

Dates.Day(dt[2]-dt[1])
# 1 day

CFTime.timeencode(dt,"days since 2000-01-01 00:00:00",DateTime360Day)
# 4-element Array{Float64,1}:
#  0.0
#  1.0
#  2.0
#  3.0

DateTime360Day(2000,1,1) + Dates.Day(360)
# DateTime360Day(2001-01-01T00:00:00)

You can replace in the example above the type DateTime360Day by the string "360_day" (the name according to the CF conversion).

Parsing dates

Dates can be parsed by using dateformat from julia's Dates module, for example:

dt = DateTimeNoLeap("21001231",dateformat"yyyymmdd");
# or
# dt = parse(DateTimeNoLeap,"21001231",dateformat"yyyymmdd")
Dates.year(dt),Dates.month(dt),Dates.day(dt)
# output (2100, 12, 31)

Acknowledgments

Thanks to Jeff Whitaker and contributors for python's cftime released under the MIT license which has helped the developpement of this package by providing reference values and a reference implementation for tests. The algorithm is based on Jean Meeus' algorithm published in Astronomical Algorithms (2nd Edition, Willmann-Bell, Virginia. p. 63, 1998) adapted to years prior to 300 AC.