Convert between various time formats relevant to Chandra.

chandra_time provides a simple interface to the C++ time conversion utility axTime3 (which itself is a wrapper for XTime) written by Arnold Rots. chandra_time also supports some useful additional time formats.

The supported time formats are:

============ ============================================== ======= Format Description System ============ ============================================== ======= secs Seconds since 1998-01-01T00:00:00 (float) tt numday DDDD:hh:mm:ss.ss... Elapsed days and time utc relday [+-] Relative number of days from now utc jd Julian Day utc mjd Modified Julian Day = JD - 2400000.5 utc date YYYY:DDD:hh:mm:ss.ss.. utc caldate YYYYMonDD at hh:mm:ss.ss.. utc fits YYYY-MM-DDThh:mm:ss.ss.. tt iso YYYY-MM-DD hh:mm:ss.ss.. utc unix Unix time (since 1970.0) utc greta YYYYDDD.hhmmss[sss] utc year_doy YYYY:DDD utc mxDateTime mx.DateTime object utc frac_year YYYY.ffffff = date as a floating point year utc ============ ============================================== =======

Each of these formats has an associated time system, which must be one of:

======= ============================ met Mission Elapsed Time tt Terrestrial Time tai International Atomic Time utc Coordinated Universal Time ======= ============================

Usage

The normal usage is to create an object that allows conversion from one time format to another. Conversion takes place by examining the appropriate attribute. Unless the time format is specified or it is ambiguous (i.e. secs, jd, mjd, and unix), the time format is automatically determined. To specifically select a format use the 'format' option.::

from chandra_time import DateTime t = DateTime('1999-07-23T23:56:00') print t.date 1999:204:23:54:55.816 t.date '1999:204:23:54:55.816' t.secs 49161360.0 t.jd 2451383.496479352 DateTime(t.jd + 1, format='jd').fits '1999-07-24T23:56:00.056' DateTime(t.mjd + 1, format='mjd').caldate '1999Jul24 at 23:54:55.820' u = DateTime(1125538824.0, format='unix') u.date '2005:244:01:40:24.000' mxd = mx.DateTime.Parser.DateTimeFromString('1999-01-01 12:13:14') DateTime(mxd).fits '1999-01-01T12:14:18.184' DateTime(mxd).date '1999:001:12:13:14.000' DateTime(mxd).mxDateTime.strftime('%c') 'Fri Jan 1 12:13:14 1999' DateTime('2007122.01020340').date '2007:122:01:02:03.400'

If no input time is supplied when creating the object then the current time is used.::

DateTime().fits '2009-11-14T18:24:14.504'

For convenience a DateTime object can be initialized from another DateTime object.

t = DateTime() u = DateTime(t)

Sequences of dates

The input time can also be an iterable sequence (returns a list) or a numpy array (returns a numpy array with the same shape)::

import numpy DateTime([1,'2001:255',3]).date ['1997:365:23:58:57.816', '2001:255:12:00:00.000', '1997:365:23:58:59.816'] DateTime(numpy.array([[1,2],[3,4]])).fits array([['1998-01-01T00:00:01.000', '1998-01-01T00:00:02.000'], ['1998-01-01T00:00:03.000', '1998-01-01T00:00:04.000']], dtype='|S23')

Date arithmetic

DateTime objects support a limited arithmetic with a delta time expressed in days. One can add a delta time to a DateTime or subtract a delta time from a DateTime. It is also possible to subtract two DateTiem objects to get a delta time in days. If the DateTime holds a NumPy array or the delta times are NumPy arrays then the appropriate broadcasting will be done. ::

d1 = DateTime('2011:200:00:00:00') d2 = d1 + 4.25 d2.date '2011:204:06:00:00.000' d2 - d1 4.25 import numpy as np d3 = d1 + np.array([1,2,3]) d3.date array(['2011:201:00:00:00.000', '2011:202:00:00:00.000', '2011:203:00:00:00.000'], dtype='|S21') (d3 + 7).year_doy array(['2011:208', '2011:209', '2011:210'], dtype='|S8')

Input and output time system

Currently the object-oriented interface does not allow you to adjust the input or output time system. If you really need to do this, use the package function convert()::

import chandra_time chandra_time.convert(53614.0, ... fmt_in='mjd', ... sys_in='tt', ... fmt_out='caldate', ... sys_out='tai') '2005Aug31 at 23:59:27.816'

The convert() routine will guess fmt_in and supply a default for sys_in if not specified. As for DateTime() the input time can be a sequence or numpy array.