Converting Timestamps in Microsconds to DateTime Format

Hello,

I am new in matlab and I need some help please!

I have a text file that contains timestamps out of a camera that captures 50 frames per second ..The data are as follows:

1 20931160389  

2 20931180407

3 20931200603  

4 20931220273  

5 20931240360 

.
.
50 20932139319

 ... and so on.

It gives also the starting time of capturing like

Date: 02.03.2012 17:57:01

The timestamps are in MICROSECONDS not in milliseconds, and matlab can support only till milliseconds but its OK for me.

Now I need to know the human format of these timestamps for each row..like

1   20931160389       02.03.2012 17:57:01.045 % just an example

2   20931180407        02.03.2012 17:57:01.066

3   20931200603        02.03.2012 17:57:01.083

4   20931220273        02.03.2012 17:57:01.105

5 20931240360   02.03.2012 17:57:01.124

and so on

I tried this:

% Reference Data

clc;    format longg

refTime = [2012,03,02,17,57,01];

refNum = datenum(refTime);

refStr = datestr(refNum,'yyyy-mm-dd HH:MM:SS.FFF');

% Processing data

dn = 24*60*60*1000*1000; % Microseconds! I have changed this equation to many options but nothing was helpful

for i = 1 : size(Data,1)
    gzTm = double(Data{i,2}); %timestamps are uint64

      gzTm2 = gzTm / dn;
      gzTm2 = refNum + gzTm2;
      gzNum = datenum(gzTm2);
      gzStr = datestr(gzNum,'yyyy-mm-dd HH:MM:SS.FFF'); % I can't use 'SS.FFFFFF'
      fprintf('i = %d\t Timestamp = %f\t TimeStr = %s\n', i, gzTm, gzStr);
  end;

But I got always strange outputs like

i = 1   Timestamp = 20931160389.000000   TimeStr = 2012-03-08 13:29:28.849

i = 2   Timestamp = 20931180407.000000   TimeStr = 2012-03-08 13:29:29.330

i = 3   Timestamp = 20931200603.000000   TimeStr = 2012-03-08 13:29:29.815

i = 4   Timestamp = 20931220273.000000   TimeStr = 2012-03-08 13:29:30.287

i = 5   Timestamp = 20931240360.000000   TimeStr = 2012-03-08 13:29:30.769

Could one help me please..! Where is my mistake?

Thanks in advance

Sam

Answer 1

[Peter Perkins]

Sam, If I understand what you're trying to do, this may be what you are looking for:

>> refTime = datenum([2012,03,02,17,57,01]);
>> datestr(refTime,'yyyy-mm-dd HH:MM:SS.FFF')

ans =

2012-03-02 17:57:01.000

>> timeStamps = [1 20931160389; 2 20931180407; 3 20931200603; 4 20931220273; 5 20931240360; 50 20932139319];
>> times = refTime + timeStamps(:,2)/(86400*1e6);
>> datestr(times,'yyyy-mm-dd HH:MM:SS.FFF')

ans =

2012-03-02 23:45:52.160
2012-03-02 23:45:52.180
2012-03-02 23:45:52.201
2012-03-02 23:45:52.220
2012-03-02 23:45:52.240
2012-03-02 23:45:53.139

[Sam]

Thanks Perkins for vectorizing this to me! It's great!

But may be I should clarify my problem more...

The time gap between each entry in the array should be nearly 20 seconds..since I have 50 frames per second(1000 millisecond / 50 = 20) which is true in your code..but the hour,minute and seconds should also indicate the initial time given as reference time because it is about some seconds earlier.

refTime = datenum([2012,03,02,17,57,01])

The output time is about six hours late than the Referenced Time

2012-03-02 23:45:52.160

which is wrong!

I expect something like:

1 20931160389 02.03.2012 17:57:01.045 % just an example

2 20931180407 02.03.2012 17:57:01.066

How you could modify your code to accomplish this?

thanks again!

Answer 2

[Peter Perkins]

You might expect that, but according to what you seemed to be describing, your timestamps represent microsecond offsets from your reference time. For example, 20931160389 microseconds is

>> 20931160389 / (1e6*60*60)

ans =

         5.8142

a little less than 6 hours. And clearly if your data are in microseconds, then they are not about 20 seconds apart. I think you mean .02s.

I can't tell you what your data mean. A datenum in MATLAB represents days and fractional days. To add x microseconds to that, you have to scale x by (86400*1e6). That's what my code does. If your data are something other than microsecond offsets, then change the code I suggested accordingly.