MATLAB: Place annotations using axis coordinates from a date-axis

Question

Hello there,

I have another problem… I want to place annotations in my plot, see the figure below.

Now, as one can see the x-axis uses datenum-numbers. How can I position the annotations using these coordinates? Each of the vertical lines should be placed at 00:00 (12PM), the dates in the center of the resulting box.

This is how far I got:

clc 
clear all 
close all 
% Get the data 
filepath=''; % Note: Im realen File gibt es natürlich einen Pfad 
fprintf('Path: %s\n', filepath) 
fprintf('\nLoad totaldev ...\n') 
totaldev = xlsread(strcat(filepath,'totaldev.xlsx')); 
fprintf(' ...done!\nLoad plant_load ...') 
plant_load = xlsread(strcat(filepath,'load.xlsx')); 
fprintf(' ...done!\n') 
data=[plant_load(:,1),plant_load(:,2),totaldev(:,2)]; 
data(:,1)=x2mdate(data(:,1)); 
fprintf('Prepare data ...\n') 
% Remove values below 0 and above 100 (plant load is 0% to 100% 
data(any(data(:,2)<0,2),:)=[]; 
data(any(data(:,2)>100,2),:)=[]; 
% Remove values below -100 and above 100 (error can't be more than +-100%) 
data(any(data(:,3)<-100,2),:)=[]; 
data(any(data(:,3)>100,2),:)=[]; 
% Compute average of time series 
% Sample rate is 2sec, so 30 values cover a minute 
data_avg=[data(:,1), movavg(data(:,2),30,30), movavg(data(:,3),30,30)]; 
data_avg(1:30,2)=data(1:30,2); 
data_avg(1:30,3)=data(1:30,3); 
fprintf(' ...done!\n') 
fprintf('\nCreate plot') 
% Plot 'em 
plot(data_avg(:,1),data_avg(:,2),data(:,1),data_avg(:,3)) 
NumTicks = 20; 
L = get(gca,'XLim'); 
set(gca,'XTick',linspace(L(1),L(2),NumTicks)) 
datetick('x','HH:MM','keepticks','keeplimits');

The function movavg will be replaced by tomorrow. The data is as follows (example) ([Time; Data1; Data2]):

735728,605428241   80,6717800000000   11,6650710000000 
735728,605451389   80,6717800000000   9,12566720000000 
735728,605474537   80,1416200000000   9,24074830000000 
735728,605497685   80,1416200000000   9,20919460000000 
735728,605520833   80,1416200000000   9,47081590000000 
735728,605543982   80,3848000000000   9,28115980000000 
735728,605567130   80,3848000000000   8,55264740000000 
735728,605590278   80,3848000000000   9,47107710000000 
735728,605613426   80,5608400000000   9,42203640000000 
735728,605636574   80,6196400000000   9,32575490000000 
735728,605659722   80,6196400000000   9,25049830000000 
735728,605682870   80,6998100000000   9,48914560000000 
735728,605706019   80,6998100000000   9,52505890000000 
735728,605729167   80,6998100000000   9,12462120000000 
735728,605752315   80,1338500000000   8,44201380000000 
735728,605775463   80,1338500000000   8,38791130000000 
735728,605798611   79,9584800000000   8,67874090000000 
735728,605821759   79,9584800000000   8,92738190000000 
735728,605844908   79,5133300000000   9,50254300000000

I have no idea now how to place the annotations using the code. Since I have to plot this figure a few times I don't want to set the annotations by hand each time …

I hope someone can help =)

Cheers from Germany

Answer 1

A start...basically, you just generate datenums that match the locations you want.

dt=datenum(2014,5,[10:12]);           % datenums for the day tick locations
xt=repmat(dt,3,1); xt=xt(:);          % and make an array of x and y locations
xt(3:3:end)=nan;                  % insert nan to break lines between locations
yt=repmat([-0.95 -1.1 nan]',3,1);     % to draw the lines at those locations (*)
hl=line(xt,yt,'color','r','clipping','off');  % lines; made red so stand out
% write the text.
ht=text(dt+0.5,-1.2*ones(size(dt)),datestr(dt,'mm.dd.yyyy'),'horizontal','center','fontsize',8);

(*) The "trick" in generating the arrays is that of inserting the NaN between the line segments to avoid drawing from the end point of the first the diagonal to the first point of the second, etc., ...

On the location for the datestr, I didn't create the other vector of locations; just used the midnight location plus 0.5 day to get noon next day for demo purposes of the idea. That works correctly for the full days in the middle, otherwise you take the average of the two datenums for the beginning and end of the partial days at the two ends.

Also, in my playing here I used a ylim(-1 1)] and the y locations for the line and the text are based on that value--you'll want to retrieve the lower y limit and adjust based on it for your case. Alternatively, you can switch to normalized coordinates relative to the whole figure and retrieve the position of the axes and work out locations therefrom. annotation works on those coordinates so if choose to go that route instead you'll have to use those. I tend to just use the axes and smudge a little. Note to get the line to show outside the axes, must set its 'clipping' property to 'off'