Concerning 1D data interpolation and use of Julian date function.

%% Loading the datas : 
load('In_Flight_Data.mat');

% Start and end dates for real-time datas obtained
DateStart = datetime('03/07/2019 17:00:00','InputFormat','dd/MM/uuuu HH:mm:ss');
DateEnd   = datetime('04/07/2019 08:00:00','InputFormat','dd/MM/uuuu HH:mm:ss');

% Datas index you want to plot
idToPlot =   [5];

datatimes = juliandate(dataTot(idat).Date(id)); % This contains the datetime values given in the first dataset.
timesim = juliandate(datethermica); %datethermica contains the datetime values given in the second dataset.
siminterpdata=interp1(timesim,datasim,datatimes); %This line gives an error

% Figure initialisation
figure
hold on
leg = {};

% Loop to plot the datas one by one
for i = 1:numel(idToPlot)
    idat = idToPlot(i);
    
    % Find the measurement points that are between the start and en dates
    id = find((dataTot(idat).Date > DateStart) & (dataTot(idat).Date < DateEnd));
    
    % Plot the data
    plot(dataTot(idat).Date(id),dataTot(idat).Value(id));
    plot(datethermica,Magneto_Board_12);

    

    
    % Put some text in the leg array, which will be used as legend
    leg{end+1} = dataTot(idat).Name;
    
end



% Format the graph
legend(leg);     % give a ledgend
ylabel('Temperature (°C)');     % Give a label to Y axis
title('Temperatures');          % Give a title

Hello everyone,

From this plot, i'am obtaining two curves, i would like to do interpolation and for that i'am using interp1. Before this i have to convert the datetime data that i'am using into juliandate.

When i try to convert to juliandate:

1) I get an error at the line indicated in the code.

2) The values that i get from 'datasim' and 'timesim' are completely same, this i dont understand why.

.............................................................................................................................................................................

Here is the data:

1) The datetime data which has been plotted in the curves:

Datetime values

'2019-07-03T16:06:48'

'2019-07-03T16:08:48'

'2019-07-03T16:09:48'

'2019-07-03T16:10:48'

'2019-07-03T16:11:48'

'2019-07-03T16:12:48'

'2019-07-03T16:13:48'

'2019-07-03T16:14:48'

'2019-07-03T16:15:48'

'2019-07-03T16:16:48'

'2019-07-03T16:17:48'

'2019-07-03T16:18:48'

'2019-07-03T16:19:48'

'2019-07-03T16:20:48'

'2019-07-03T16:21:48'

'2019-07-03T16:22:48'

'2019-07-03T16:23:48'

'2019-07-03T16:24:48'

'2019-07-03T16:25:48'

'2019-07-03T16:26:48'

'2019-07-03T17:08:43'

'2019-07-03T17:11:43'

'2019-07-03T17:14:43'

'2019-07-03T17:17:43'

'2019-07-03T17:23:43'

'2019-07-03T17:29:44'

'2019-07-03T17:32:44'

'2019-07-03T17:35:44'

'2019-07-03T17:38:44'

'2019-07-03T17:41:44'

'2019-07-03T17:47:44'

'2019-07-03T17:50:44'

'2019-07-03T17:53:44'

'2019-07-03T17:56:44'

'2019-07-03T17:59:45'

'2019-07-03T18:02:45'

'2019-07-03T18:05:45'

'2019-07-03T18:08:45'

'2019-07-03T18:11:45'

'2019-07-03T18:14:45'

Temperature values

24

24

24

24

24

24

24

24

24

24

25

25

25

25

25

25

24

24

25

25

18

15

16

13

9

8

5

4

1

0

0

-1

-1

-1

2

3

4

6

5

7

This was the data for the blue curve seen in the graph.

........................................................................................................................................

Datetime values

'03-Jul-2019 10:00:00'

'03-Jul-2019 10:00:20'

'03-Jul-2019 10:00:40'

'03-Jul-2019 10:01:00'

'03-Jul-2019 10:01:20'

'03-Jul-2019 10:01:40'

'03-Jul-2019 10:02:00'

'03-Jul-2019 10:02:20'

'03-Jul-2019 10:02:40'

'03-Jul-2019 10:03:00'

'03-Jul-2019 10:03:20'

'03-Jul-2019 10:03:40'

'03-Jul-2019 10:04:00'

'03-Jul-2019 10:04:20'

'03-Jul-2019 10:04:40'

'03-Jul-2019 10:05:00'

'03-Jul-2019 10:05:20'

'03-Jul-2019 10:05:40'

'03-Jul-2019 10:06:00'

'03-Jul-2019 10:06:20'

'03-Jul-2019 10:06:40'

'03-Jul-2019 10:07:00'

'03-Jul-2019 10:07:20'

'03-Jul-2019 10:07:40'

'03-Jul-2019 10:08:00'

'03-Jul-2019 10:08:20'

'03-Jul-2019 10:08:40'

'03-Jul-2019 10:09:00'

'03-Jul-2019 10:09:20'

'03-Jul-2019 10:09:40'

'03-Jul-2019 10:10:00'

'03-Jul-2019 10:10:20'

'03-Jul-2019 10:10:40'

'03-Jul-2019 10:11:00'

'03-Jul-2019 10:11:20'

'03-Jul-2019 10:11:40'

'03-Jul-2019 10:12:00'

'03-Jul-2019 10:12:20'

'03-Jul-2019 10:12:40'

'03-Jul-2019 10:13:00'

Temperature values

25

24.7111000000000

24.3868000000000

24.0395000000000

23.6765000000000

23.3022000000000

22.9195000000000

22.5301000000000

22.1357000000000

21.7374000000000

21.3361000000000

20.9328000000000

20.5283000000000

20.1231000000000

19.7179000000000

19.3132000000000

18.9095000000000

18.5072000000000

18.1065000000000

17.7079000000000

17.3116000000000

16.9178000000000

16.5267000000000

16.1384000000000

15.7531000000000

15.3709000000000

14.9919000000000

14.6162000000000

14.2439000000000

13.8749000000000

13.5093000000000

13.1472000000000

12.7885000000000

12.4333000000000

12.0815000000000

11.7332000000000

11.3884000000000

11.0471000000000

10.7091000000000

10.3746000000000

This is the data for the Green curve in the graph.

......................................................................................................................

What i'am doing is first trying to convert these datatime values to juliandate and they are coming the same. And then there is the error at the line i indicated above. Also please tell me how i could interpolate after having resolved these issues.

[Steven Lord]

What is the full and exact text of the error message you receive on that line? Include all the text displayed in red in a comment, and if you see any text displayed in orange include that text as well.

[Amal Rai]

>> Code_for_real_datas

Undefined function or variable 'datasim'.

Error in Code_for_real_datas (line 51)

siminterpdata=interp1(timesim,datasim,datatimes)

This is the error. How do i define datasim, i checked on MATLAB help and it shows that 'datasim' would contain the corresponding values of the sample points of 'timesim'. I don't understand.

Also, what about the Juliandate function, it is giving me the same values for both the datasets.

Answer 1

[Walter Roberson]

Change

load('In_Flight_Data.mat');

To

Ds = load('In_Flight_Data.mat');
dataTot = Ds.dataTot;
datethermica = Ds.datethermica;
datasim = Ds.datasim;

That is, when you use load() without any output variable, newer versions of MATLAB are permitted to refuse to recognize any variable poofed into existence.

If datasim is not a variable inside your mat file then what exactly are you interpolating?