Convert Date and Time to Julian Date or POSIX Time
You can convert datetime arrays to represent points in time in specialized numeric formats. In
general, these formats represent a point in time as the number of seconds or days that have elapsed
since a specified starting point. For example, the Julian date is the number of days and fractional days
that have elapsed since the beginning of the Julian period. The POSIX® time is the number of
seconds that have elapsed since 00:00:00 1-Jan-1970 UTC (Universal Coordinated Time). MATLAB®
provides the juliandate and posixtime functions to convert datetime arrays to Julian dates and
POSIX times.
While datetime arrays are not required to have a time zone, converting "unzoned" datetime values
to Julian dates or POSIX times can lead to unexpected results. To ensure the expected result, specify
the time zone before conversion.
Specify Time Zone Before Conversion
You can specify a time zone for a datetime array, but you are not required to do so. In fact, by
default the datetime function creates an "unzoned" datetime array.
Create a datetime value for the current date and time.
d = datetime('now')
d = datetime
01-Sep-2021 16:01:28
d is constructed from the local time on your machine and has no time zone associated with it. In many
contexts, you might assume that you can treat the times in an unzoned datetime array as local
times. However, the juliandate and posixtime functions treat the times in unzoned datetime
arrays as UTC times, not local times. To avoid any ambiguity, it is recommended that you avoid using
juliandate and posixtime on unzoned datetime arrays. For example, avoid using
posixtime(datetime('now')) in your code.
If your datetime array has values that do not represent UTC times, specify the time zone using the
TimeZone name-value pair argument so that juliandate and posixtime interpret the datetime
values correctly.
d = datetime('now','TimeZone','America/New_York')
d = datetime
01-Sep-2021 16:01:28
As an alternative, you can specify the TimeZone property after you create the array.
d.TimeZone = 'America/Los_Angeles'
d = datetime
01-Sep-2021 13:01:28
To see a complete list of time zones, use the timezones function.
Convert Date and Time to Julian Date or POSIX Time
7-7
You can convert datetime arrays to represent points in time in specialized numeric formats. In
general, these formats represent a point in time as the number of seconds or days that have elapsed
since a specified starting point. For example, the Julian date is the number of days and fractional days
that have elapsed since the beginning of the Julian period. The POSIX® time is the number of
seconds that have elapsed since 00:00:00 1-Jan-1970 UTC (Universal Coordinated Time). MATLAB®
provides the juliandate and posixtime functions to convert datetime arrays to Julian dates and
POSIX times.
While datetime arrays are not required to have a time zone, converting "unzoned" datetime values
to Julian dates or POSIX times can lead to unexpected results. To ensure the expected result, specify
the time zone before conversion.
Specify Time Zone Before Conversion
You can specify a time zone for a datetime array, but you are not required to do so. In fact, by
default the datetime function creates an "unzoned" datetime array.
Create a datetime value for the current date and time.
d = datetime('now')
d = datetime
01-Sep-2021 16:01:28
d is constructed from the local time on your machine and has no time zone associated with it. In many
contexts, you might assume that you can treat the times in an unzoned datetime array as local
times. However, the juliandate and posixtime functions treat the times in unzoned datetime
arrays as UTC times, not local times. To avoid any ambiguity, it is recommended that you avoid using
juliandate and posixtime on unzoned datetime arrays. For example, avoid using
posixtime(datetime('now')) in your code.
If your datetime array has values that do not represent UTC times, specify the time zone using the
TimeZone name-value pair argument so that juliandate and posixtime interpret the datetime
values correctly.
d = datetime('now','TimeZone','America/New_York')
d = datetime
01-Sep-2021 16:01:28
As an alternative, you can specify the TimeZone property after you create the array.
d.TimeZone = 'America/Los_Angeles'
d = datetime
01-Sep-2021 13:01:28
To see a complete list of time zones, use the timezones function.
Convert Date and Time to Julian Date or POSIX Time
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