RE: Convert Epoch Date to Serial Date

[Bård Skaflestad]

If you're willing to ignore leap seconds and either don't need or can perform 
your own time-zone conversions from UTC to local time, you can get pretty far 
by exploiting the fact that 'datenum' does proper duration handling.  You can 
pass your epoch value as the sixth column in an argument to 'datenum' and add 
datenum([1970, 0, 0]) to the result:

    epoch = 2147483647;  # Some epoch value
    datevec(datenum([1970,0,0]) + datenum([zeros(10,5), epoch + (0:9).']))

    ans =
       2038      1     18      3     14      7
       2038      1     18      3     14      8
       2038      1     18      3     14      9
       2038      1     18      3     14     10
       2038      1     18      3     14     11
       2038      1     18      3     14     12
       2038      1     18      3     14     13
       2038      1     18      3     14     14
       2038      1     18      3     14     15
       2038      1     18      3     14     16

This is just a small extension of the method suggested below.


Regards,

Bård Skaflestad
SINTEF Digital, Mathematics & Cybernetics
Compuational Geosciences group

-----Original Message-----
From: Help-octave <address@hidden> On Behalf Of Fritz Sonnichsen
Sent: Wednesday, April 10, 2019 9:04 PM
To: Richardson, Anthony <address@hidden>; Help GNU Octave <address@hidden>
Subject: Re: Convert Epoch Date to Serial Date

Thanks Anthony.
   That seems to work after some code like this.
     t=localtime(epoch_date)
bf=sprintf("%d/%d/%d,%d:%d:%d",t.year+1900,t.mon+1,t.mday,t.hour,t.min,t.sec)
     DTformat='yyyy/mm/dd,HH:MM:SS';
     datenum(bf,DTformat)
     numerical_date = datenum(bf,DTformat); %days from January 0, 0000

after some thought the same result can be obtained as follows;
     numerical_date=  dtetmenum(1)/86400 + datenum(1970,1,1)

would be nice if this was included as an "epoch2serial" utility just to keep 
make it easy to remember!

cheers
Fritz

On 4/10/2019 2:33 PM, Richardson, Anthony wrote:
>> Subject: Convert Epoch Date to Serial Date
>>
>> I've looked thru the Octave time utilities and could not find a 
>> routine for this purpose. Is there a simple function that receives 
>> the epoch-date and converts it to a serial-date. (I need to feed the 
>> latter to the datetick routine)
>>
>> Thanks
>> Fritz
> I believe localtime will return a structure that you can pull apart and feed 
> to datenum to get a serial date:
>
>>> localtime(time())
> ans =
>
>    scalar structure containing the fields:
>
>      usec =  839628
>      sec =  31
>      min =  32
>      hour =  13
>      mday =  10
>      mon =  3
>      year =  119
>      wday =  3
>      yday =  99
>      isdst =  1
>      gmtoff = 0
>      zone = Central Daylight Time
>
>
> Tony Richardson
>