Conversion of Gregorian date to decimal years

Hi,

I have time series given in gregorian time in seconds since 1992-01-01 00:00:00'. For example; 23853938,23853939...

How can i convert this gregorian time seconds to decimal years like 2010.544, 2010.545...

Answer 1

[Walter Roberson]

basetime = datetime('1992-01-01 00:00');

gtime =  23853938

t1 = basetime + seconds(gtime)
t2 = dateshift(t1, 'start', 'year')
t3 = dateshift(t1, 'end', 'year')
fy = year(t1) + (t1-t2)./(t3-t2)

[Walter Roberson]

This assumes fraction of actual year, taking into account leap year, not fraction of fixed length year.

[Ahmet Hakan UYANIK]

it is giving similar results as I did actually, what I do is;

T = datetime(1992,1,1) + seconds(gtime);
T.Format = 'yyyy-MM-dd HH:mm:ss'; 
dy = decyear(T)

both are correct, I guess :) Thank you in advance

[Walter Roberson]

decyear() appears to require the Areospace Toolbox.

Also, setting the Format is not required for decyear()

[Will]

This won't match decyear() as (t3-t2) is not the exact length of the year. decyear() calculates the fractional year as (t1-t2)/(number of hours in year or leap year).

Without the aerospace toolbox you can use:

t3 = t2 + calyears(1);
fy = year(t1) + (t1-t2)./(t3-t2)

or with dateshift(), shift to the equivalent time in the year before or after to get the correct length duration, e.g.

t3 = dateshift(t1, 'end', 'year')
t4 = dateshift(datetime(year(t1)-1,1,1), 'end' ,'year');
fy = year(t1) + (t1-t2)./(t3-t4)