geoscitime.py

# Class: GeoSciTime
# Contents: Time systems used in geoscientific programming
# Functions: date2mjd, mjd2date, date2toy, toy2date, others date parse already captured by strptime ..
# Author: Simran Suresh
# Date: 16.04.2022

# TODO: https://gssc.esa.int/navipedia/index.php/Transformations_between_Time_Systems
# sidereal year, day 365.25, 23:56 min

import math


def mjd2jd(mjd):
    """
    converts mjd to jd
    args: modified julian date
    returns: jd
    """
    return mjd + 2400000.5


def jd2mjd(jd):
    """
    converts jd to mjd
    args: julian date
    returns: mjd
    """
    return jd - 2400000.5


def date2mjd(year, month, day):
    """
    SRC: Algorithm from 'Practical Astronomy with your Calculator or Spreadsheet', 
    4th ed., Duffet-Smith and Zwart, 2011.
    args: year, month, day in format yyyy, mm, dd 
    returns: modified julian date mjd
    """
    if month == 1 or month == 2:
        yearp = year - 1
        monthp = month + 12
    else:
        yearp = year
        monthp = month

    # beginning of the Gregorian calendar check.
    if ((year < 1582) or
        (year == 1582 and month < 10) or
        (year == 1582 and month == 10 and day < 15)):
        # before start
        B = 0
    else:
        # after start
        A = math.trunc(yearp / 100.)
        B = 2 - A + math.trunc(A / 4.)
        
    C = math.trunc((365.25 * yearp) - 0.75) if yearp < 0 \
                                            else math.trunc(365.25 * yearp)
    D = math.trunc(30.6001 * (monthp + 1))

    jd = B + C + D + day + 1720994.5
    
    return jd2mjd(jd)


def mjd2date(mjd):
    """
    SRC: Algorithm from 'Practical Astronomy with your Calculator or Spreadsheet', 
    4th ed., Duffet-Smith and Zwart, 2011.
    args: modified julian date
    returns: tuple of year, month, day
    """
    jd = mjd2jd(mjd) + 0.5

    F, I = math.modf(jd)
    I = int(I)
    A = math.trunc((I - 1867216.25)/36524.25)
    
    B = I + 1 + A - math.trunc(A / 4.) if I > 2299160 \
                                        else I
        
    C = B + 1524
    D = math.trunc((C - 122.1) / 365.25)
    E = math.trunc(365.25 * D)
    G = math.trunc((C - E) / 30.6001)
    
    day = C - E + F - math.trunc(30.6001 * G)
    
    month = G - 1 if G < 13.5 \
                    else G - 13
        
    year = D - 4716 if month > 2.5 \
                    else D - 4715
        
    return year, month, day


def date2percent(year, month, day):
    """
    convert date to percent of the year
    eg: 2022, 5, 12 => 2022.3616438356164 and 2020, 1, 12 => 2020.032786885246
    args: year, month, day
    returns: year.percent
    """
    days_num = {1:31, 2:28, 3:31, 4:30, 5:31, 6:30, 7:31, 8:31, 9:30, 10:31, 11:30, 12:31}
    
    # leap year check
    if year % 4 == 0:
        days_num[2] = 29

    # for first month, days elapsed is number of days
    if month == 1:
        days_elapsed = day
    else:
    # for remaining months, it is total number of days till previous month and days in current month
        days_elapsed = sum([val for key, val in days_num.items() if key < month]) + day

    # percent of the year
    return days_elapsed/sum(days_num.values()) + year