3.4.4. HOWTO: Convert UHDAS Dates

3.4.4.1. Definitions:

  • ISO-8601 Calendar dates [wikipedia: ISO_8601#Calendar_dates]

    YYYY-MM-DD

  • UHDAS: $UNIXD or $PYRTM

    YYYY-DDD (DDD: 01 Jan = 000)

    The day-of-year is zero based.

  • Ordinal Date (or Day of year) [wikipedia: ordinal date; ISO_8601#Ordinal_date]

    YYYY-DDD (DDD: 01 Jan = 001)

  • Julian Day [wikipedia: Julian_day]

    Days since 4713-01-01 BC (noon UTC JD 1 = 0.0)

  • Unix (or POSIX) Time [wikipedia: Unix_time]

    Seconds since 1970-01-01 00:00:00 UTC Note: 1970-01-01 was day 0 (zero).

3.4.4.2. Conversions:

3.4.4.2.1. UHDAS to Calendar date:

UHDAS utility: /usr/local/currents/bin/to_date

usage:

to_date [YY]YY DDD[.ddd]

where:

  • [YY]YY (year) is either 2 or 4 digits

  • DDD (day) is the zero based day of year (01 Jan = 0)

  • [.ddd] (fractional day)

Example:

to_date 2018 322.33
2018/11/19  07:55:12.00

3.4.4.2.2. Calendar to UHDAS date:

UHDAS utility: /usr/local/currents/bin/to_day

usage:

to_day [YY]YY [YY]YY MM DD hh mm ss

where:

  • [YY]YY (year) is either 2 or 4 digits (beginning of cruise)

  • [YY]YY (year) is either 2 or 4 digits (end of cruise)

  • MM (month)

  • DD (day) is the zero based day of year (01 Jan = 0)

  • hh (hour of day, UTC)

  • mm (minutes)

  • ss (seconds)

Note

Two year-values are required to account for cruises that wrap a year-end.

Example:

to_day 2017 2018 01 19 06 00 # cruise starts 2017, ends 2018 383.25000000

to_day 2018 2018 11 19 08 00 # cruise is all within 2018 322.33333333

Linux utility: /bin/date

usage:

date [OPTION] ... [+FORMAT]

where:

OPTIONS
-d, --date=DATESTR
             display time described by STRING, not 'now'
FORMAT
%j     day of year (001..366)
DATESTR

“N day ago”    where N is an integer number of days
“-N day”       where N is an integer number of days

various date formats, such as YYYY-MM-DD
combinations of the above

Examples:
date -d "-1 day 2018-11-19" +"%j"
322

date -d "1 day ago  2018-11-19" +"%j"
322

Note

since the Unix “%j” is day-of-year starting at 1 (one), we need to subtract a day to make the conversion zero-based.