MATLAB: Converting GPS time to Local Time

gps to lttime conversion

hi. Im relatively new to Matlab and i have been trying to analyze a set of GPS data which has the time of the day in GPS format. the raw data has time of day stored in a matlab variable 't' as:

The difference between 2 consecutive GPS time is 60 sec. some time values are repeated, meaning 2 readings where taken for that particular minute.

i.e.

432060= 00:01 UT= 12:01 LT
402060= 00:01 UT= 12:01 LT
432120= 00:02 UT= 12:02 LT

and so forth

I have been trying to convert this 6 digit numbers stored in variable 't' to HH:MM LT format (storing it in variable t2) using various examples and codes on this forum and from YouTube but have so far failed.

i would be grateful if someone can help me with the conversion. btw Fiji time is UT +12hr.

Best Answer

t2=datestr(seconds(t)+hours(12),'HH:MM')

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MATLAB: Timezone to UTC: How to add duration vector to datetime vector

Frank, what's up is Daylight Saving Time, which occurred on March 8th this year. I'm guessing you knew that, but got mixed up in the time arithmetic. Here's what's going on. You have this:

>> time = ['2015/03/08 00:00';'2015/03/08 01:00';'2015/03/08 03:00';'2015/03/08 04:00'];
>> Time = datenum(time,'yyyy/mm/dd HH:MM')
Time =
                    736031
          736031.041666667
                736031.125
          736031.166666667

datenums don't know anything about time zones or DST. Those times mean whatever you want them to mean. Since you then do this ...

>> date = datetime(Time,'ConvertFrom','datenum','Timezone','America/Montreal')
date = 
   08-Mar-2015 00:00:00
   08-Mar-2015 01:00:00
   08-Mar-2015 03:00:00
   08-Mar-2015 04:00:00

... I assume you mean that those datenums are to be interpreted as times in the America/Montreal time zone. But what you've left out is this:

>> date.Format = [date.Format ' z']
date = 
   08-Mar-2015 00:00:00 UTC-5
   08-Mar-2015 01:00:00 UTC-5
   08-Mar-2015 03:00:00 UTC-4
   08-Mar-2015 04:00:00 UTC-4

The second and third times are only an hour apart. Then this ...

>> [UTC_Offset,dst] = tzoffset(date);
>> Date = date - UTC_Offset
Date = 
   08-Mar-2015 06:00:00 UTC-4
   08-Mar-2015 07:00:00 UTC-4
   08-Mar-2015 07:00:00 UTC-4
   08-Mar-2015 08:00:00 UTC-4

... adds 5 hours to the first and second times, but adds only 4 hours to the third and fourth times. But you're doing the addition in the America/Montreal time zone. Adding 5 hours to the first two puts them after the DST shift @2am, which makes them look like you added 6 hours. In other words, your array is not UTC, it's shifted America/Montreal. The easiest thing to do to get UTC times is this:

>> date.TimeZone = 'UTC'
date = 
   08-Mar-2015 05:00:00 UTC
   08-Mar-2015 06:00:00 UTC
   08-Mar-2015 07:00:00 UTC
   08-Mar-2015 08:00:00 UTC

Hope this helps.

MATLAB: Convert hourly temperature data into daily in the specific time interval

If this is in a datetime variable type, how about you offset your original time by 1 hr (e.g., yourVarName - hours(1)). After that you can group them by date and perform average over each group (consider using findgroups function). This can be done easily using splitapply function if this is a table variable.

Best Answer

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MATLAB: Timezone to UTC: How to add duration vector to datetime vector

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