MATLAB - best way to dynamically update a line handles' XData and YData? - matlab

I am collecting data and plotting that data in real time. The data are produced by a motion capture system. I have one class DynamicDataset that is just a wrapper around a 2-column matrix (although it's more nuanced than that) with an event notifier for new data added; another class DynamicPlotter that listens for the data-added event and updates the plot dynamically. Appropriate code snippets:
classdef DynamicDataset < handle
properties
newestData = [];
data = []
end
events
DataAdded
end
methods
function append(obj, val)
obj.data(end+1,:) = val;
obj.newestData = val;
notify(obj, 'DataAdded');
end
end
end
classdef DynamicPlotter < dynamicprops
properties
FH %# figure handle
AH %# axes handle
LH %# array of line handles - may have multiple lines on the plot
dynProps = {} %# cell array of dynamic property names -
%# use to access individual datasets
end
methods
function obj = DynamicPlotter(props) %# props is a cell array of dynamic
%# properties to store information
for i = 1:length(props)
addprop(obj, props{i});
obj.(props{i}) = DynamicDataset;
obj.dynProps = [obj.dynProps props{i}];
addlistener(obj.(props{i}), 'DataAdded', #obj.updatePlot(i));
end
obj.createBlankPlot();
end
function createBlankPlot(obj)
obj.FH = figure;
obj.AH = axes;
hold all;
for i = 1:length(obj.dynProps)
obj.LH(i) = plot(nan); %# only used to produce a line handle
set(obj.LH(i), 'XData', [], 'YData', []);
end
end
function updatePlot(obj, propNum)
X = get(obj.LH(propNum), 'XData');
Y = get(obj.LH(propNum), 'YData');
X(end+1) = obj.(dynProps{propNum}).newestData(1);
Y(end+1) = obj.(dynProps{propNum}).newestData(2);
set(obj.LH(propNum), 'XData', X, 'YData', Y);
end
end
end
Based on the MATLAB Code Profile, the set command in updatePlot() is rather expensive. I am wondering if there is a better way to plot individual points as they come? Ideally I would push the single point into XData and YData and draw that point only, but I don't know if this is possible.
Please note that there may be multiple lineseries objects (i.e., multiple graphs on the same plot); plot() takes an axes handle as an argument, so it wouldn't consider the properties of the previously drawn line handles (or is there a way to make it do so?); I thought of just doing plot(x,y);hold all; but that would give me separate line handles every time, each corresponding to a single point.
It might be that there's no way to make plotting incoming points any faster, but I figured I'd ask.
EDIT: Updated OP with actual code I'm working with, rather than using a generic example that's up for misinterpretation.

The amount of data you're handling in each update, is large (although only a single point is actually changing), making your code O(N^2).
By using a second lineseries to build up a large group of data, you can alternate between adding every point to a short "active" line, and infrequently adding large blocks to the main lineseries. While this doesn't exactly avoid O(N^2), it lets you reduce the constant significantly.
If you do this, remember to overlap the "old" lineseries and "active" lineseries by one point, so that they connect.
Essentially:
function updatePlot(obj, propNum)
X = get(obj.LHactive(propNum), 'XData');
Y = get(obj.LHactive(propNum), 'YData');
X(end+1) = obj.(dynProps{propNum}).newestData(1);
Y(end+1) = obj.(dynProps{propNum}).newestData(2);
if numel(X) > 100
Xold = [get(obj.LH(propNum), 'XData'); X(2:end)];
Yold = [get(obj.LH(propNum), 'YData'); Y(2:end)];
set(obj.LH(propNum), 'XData', Xold, 'YData', Yold);
X = X(end);
Y = Y(end);
end
set(obj.LHactive(propNum), 'XData', X, 'YData', Y);
end

Part of the reason why your code may be taking a long time to run is because you are using a for loop to assign your variables. Depending on what version of Matlab you are using, this will slow your process down significantly. I suggest using vectorization to assign values to your x and y like this:
x = 1:1000;
y = cosd(x);
You can then assign the first points in your data.
xi = x(1);
yi = y(1);
When you plot, assign the XDataSource and YDataSource.
h = plot(xi, yi, 'YDataSource', 'yi', 'XDataSource', 'xi');
Now when you loop through to change the values, use the refreshdata to update the Xdata and Ydata values. Use the drawnow function to update the figure window.
for k = 2:1000,
xi = x(1:k);
yi = y(1:k);
refreshdata(h, 'caller')
drawnow;
end

Your code is slow, because you are replotting all values everytime that you call updatePlot. I would therefore only plot the latest point in updatePlot (This is also the problem that you've stated: Ideally I would push the single point into XData and YData and draw that point only, but I don't know if this is possible.)
add property LH_point_counter
classdef DynamicPlotter < dynamicprops
properties
FH %# figure handle
AH %# axes handle
LH %# cell array of line handles - may have multiple lines on the plot
% counter that counts home many points we have for each dynProps
LH_point_counter = [];
dynProps = {} %# cell array of dynamic property names -
%# use to access individual datasets
end
modify updatePlot
function updatePlot(obj, propNum)
% plot new point
new_x = obj.(dynProps{propNum}).newestData(1);
new_y = obj.(dynProps{propNum}).newestData(2);
new_handle = plot(new_x, new_y);
% add new handle to list of handles of this property
counter_this_prop = obj.LH_point_counter(propNum);
counter_this_prop = counter_this_prop + 1;
obj.LH{propNum}(counter_this_prop) = new_handle;
% save new counter value
obj.LH_point_counter(propNum) = counter_this_prop;
end

Related

How to plot in realtime properly? (from a serialport) Matlab

I am reading data from a serialport using callback terminator:
configureCallback(s,"terminator",#readSerialData)
I want to plot this data in real time. So what I do is to use a global structure of arrays where the gathered data is stored in every new row. There are different arrays because I need to classify different sources of data
I use a function "createfigure" inside the #readSerialData, which plots the array of the corresponding source of incoming data.
However, this becomes extremely laggy, so this must not be the right way to do...
Also, in the graphs I want to see all the arrays plotted in once. But the result is that it only plots the last received array on top of the other plots. So it accumulates lines on top of each other, making the axes illegible
function createfigure2(source,X1,Y1)
% X1: vector of x data
% Y1: vector of y data
% Auto-generated by MATLAB on 21-Jan-2021 13:54:53
% Create figure
figure1 = figure(1);
hold on;
% Create axes
axes1 = axes('Parent',figure1,...
'Position',[0.109498680738786 0.69811320754717 0.800791556728232 0.273584905660377]);
hold(axes1,'on');
% Create plot
plot(X1,Y1,'DisplayName',source,'Parent',axes1,'Marker','*','LineWidth',0.01,...
'LineStyle',':');
end
You can create a plot object (parameter returned when calling the plot function) and send it to the callback itself by setting it as a parameter of "BytesAvailableFcn". Then update the plot directly inside the callback.
function mainFunction()
figure1 = figure();
axes1 = axes('Parent',figure1,...
'Position',[0.109498680738786 0.69811320754717 0.800791556728232 0.273584905660377]);
numParams = 4;
plotObjects = cell(1,numParams);
plotObjects{1} = plot(nan,nan,'r-','parent',axes1);
hold(axes1, 'on');
plotObjects{2} = plot(nan,nan,'g-','parent',axes1);
plotObjects{3} = plot(nan,nan,'b-','parent',axes1);
plotObjects{4} = plot(nan,nan,'k-','parent',axes1);
hold(axes1, 'off');
sp = openSerialPort('COM9', plotObjects);
...
end
function sp = openSerialPort(portName, plotObjects)
% intialize your com port here
sp = serial(portName);
sp.BaudRate = 9600;
...
sp.BytesAvailableFcn = {#plotMyData, plotObjects}
end
function plotMyData(sp, ~, plotObjects)
% read the data from the serial port...
[dataVectX, dataVectY] = get_data_from_serial...
% This considers that dataVectX and Y contains the readings of 4...
% different sensors where dataVectX(1) is the first sensor, dataVectX(2) is...
% the second sensor, and so one.
% update data
for paramID = 1:4
plotObjects{paramID}.XData = dataVectX(paramID);
plotObjects{paramID}.YData = dataVectY(paramID);
end
% if you wanted to append the data instead of replacing it you can either use
% plotObjects{paramID}.XData = [plotObjects{paramID}.XData, newXVector]; % use this if x is a vector
% plotObjects{paramID}.YData = [plotObjects{paramID}.YData, newYVector];
% or
% plotObjects{paramID}.XData(end+1) = dataVectX(paramID); % use this if x is a single value
% plotObjects{paramID}.YData(end+1) = dataVectY(paramID);
drawnow();
end

Handling and eliminating multiples entries in MatLab legend

I currently want to have the legend of graph, however i'm plotting several lines that should be group in only 3 types.
My currently option is to use a dummy plot out of the boundaries, plotting the relevant data and calling the legend just at the end. It works but it is prone to errors. I wanted to update the legend and select just a few of the plots.
I tried to use the leg_handle.String, but then it comes two problems:
It still plot 5 handles instead of 3.
It does not have the proper line style & color.
Any ideas?
Bellow follow the code (with dummy plot commented) and the pictures of the current version giving the error and what i want to look.
clear
figure()
hold on
%using
%dummy plot
% leg_text={'a','b','c'};
% plot(100,100,'-r')
% plot(100,100,'-b')
% plot(100,100,'-k')
for ii=1:20,
plot(1:11,linspace(0,ii,11),'-r')
end
for ii=30:50,
plot(1:11,linspace(0,ii,11),'-b')
end
for ii=70:80,
plot(1:11,linspace(ii,25,11),'-k')
end
Yaxl=[-1 80];
Xaxl=[1 11];
set(gca, 'Visible','on', ...
'Box','on', ...
'Layer','top',...
'Xlim',Xaxl, ...
'Ylim',Yaxl);
%using
% legend(leg_text)
%want to use
leg_hand=legend(gca,'show');
leg_hand.String=leg_hand.String([1 21 42]);
%extra comand will give the things that i wanted above
% leg_hand.String=leg_hand.String([1 2 3]);
What it gives:
What I expect to have:
I have tried this method using [a,b,c,d]=legend, but this give only the a handle that i already using.
This little workaround should do the job:
clear();
figure();
hold on;
h = gobjects(3,1);
for ii = 1:20
h(1) = plot(1:11,linspace(0,ii,11),'-r');
end
for ii = 30:50
h(2) = plot(1:11,linspace(0,ii,11),'-b');
end
for ii = 70:80
h(3) = plot(1:11,linspace(ii,25,11),'-k');
end
set(gca,'Box','on','Layer','top','Visible','on','Xlim',[1 11],'Ylim',[-1 80]);
legend(h,'A','B','C');
hold off;
Actually, what I did is very simple. I created an array of graphical objects of size 3 (one for each iteration) using the gobjects function. Then, inside each iteration, I assigned the last plotted line to its respective array placeholder. Finally, I created the legend using the three graphical objects I previously stored.
Alternatively:
clear();
figure();
hold on;
h1 = gobjects(20,1);
for ii = 1:20
h1(ii) = plot(1:11,linspace(0,ii,11),'-r');
end
h2 = gobjects(21,1);
for ii = 30:50
h2(ii-29) = plot(1:11,linspace(0,ii,11),'-b');
end
h3 = gobjects(11,1);
for ii = 70:80
h3(ii-69) = plot(1:11,linspace(ii,25,11),'-k');
end
set(gca,'Box','on','Layer','top','Visible','on','Xlim',[1 11],'Ylim',[-1 80]);
legend([h1(1) h2(1) h3(1)],'A','B','C');
hold off;
You create an array of graphical objects for storing the plot handlers produced by every iteration. Then you create the legend using the first (basically, any) item of each array of graphical objects.

Plot to figures without bringing them into foreground

figure;
ax1 = axes;
figure;
ax2 = axes;
x = 0; y = 0;
while ishandle(ax1) && ishandle(ax2)
x = x + 1;
y = y + 1;
figure(1)
scatter(x,y, 'MarkerEdgeColor', 'red')
hold on
figure(2)
scatter(x,y, 'MarkerEdgeColor', 'blue')
hold on
end
In my script I have multiple figures, which are going to be updated in a loop. The figures have to be displayed, while the script is running. Unfortunately the currently updated figure is always popping in the foreground, which makes it impossible to monitor a certain figure. I understand that the calling of figure(1) and figure(2) causes this behaviour, but I how can I plot to these figures, without bringing the window into foreground?
As mikkola suggested in a comment, you can specify to which axes scatter or plot add data points. However, there is a better method: create a single line object, and update its xdata and ydata properties. This is both faster and more memory efficient. Your code would become:
x = 0; y = 0;
figure;
h1 = plot(x,y,'ro');
figure;
h2 = plot(x,y,'bo');
while ishandle(h1) && ishandle(h2)
x = x + 1;
y = y + 1;
h1.XData(end+1) = x;
h1.YData(end+1) = y;
h2.XData(end+1) = x;
h2.YData(end+1) = y;
drawnow
pause(0.1)
end
I keep a set of rules of thumb for when working with MATLAB handle graphics. These are relevant to this question:
Use figure only to create a new figure, or to bring an existing figure to the front (which you want to avoid in general, but sometimes is necessary).
Always specify with which figure or axes you want to work, by keeping and using their handles. I never rely on gcf or gca (not explicitly nor implicitly). Using the current figure is useful when typing on the command line, but in a script or a function there is the real danger than someone clicks randomly on windows while the function is executing. Creating a window then writing to gcf could end up writing to a different figure (really, I click on random things all the time).
Don't create more objects than necessary. Creating a new line object for every point you plot is wasteful.
Note also that plot(...'o') is equivalent to scatter(...) unless you specify a different color or size for each point. But using the dot size or color to specify additional information is not a good way to convey that information. Read Tufte's "The visual display of quantitative information" if you're interested in learning about effective communication through graphs.
The relevant part can be found in the part of the documentation of scatter that includes the input ax:
scatter(ax,___) plots into the axes specified by ax instead of into
the current axes.
This allows the user to specify an axis handle pointing to which axes should be used for drawing the scatter plot. Thus if you skip using figure in your code and use the ax input instead, you avoid the "bring to front" behavior associated with figure.
You can modify your code as follows:
figure;
ax1 = axes;
figure;
ax2 = axes;
x = 0; y = 0;
while ishandle(ax1) && ishandle(ax2)
x = x + 1;
y = y + 1;
scatter(ax1, x,y, 'MarkerEdgeColor', 'red')
hold on
scatter(ax2, x,y, 'MarkerEdgeColor', 'blue')
hold on
end

Matlab update plot with multiple data lines/curves

I want to update a plot with multiple data lines/curves as fast as possible. I have seen some method for updating the plot like using:
h = plot(x,y);
set(h,'YDataSource','y')
set(h,'XDataSource','x')
refreshdata(h,'caller');
or
set(h,'XData',x,'YData',y);
For a single curve it works great, however I want to update not only one but multiple data curves. How can I do this?
If you create multiple plot objects with a single plot command, the handle returned by plot is actually an array of plot objects (one for each plot).
plots = plot(rand(2));
size(plots)
1 2
Because of this, you cannot simply assign another [2x2] matrix to the XData.
set(plots, 'XData', rand(2))
You could pass a cell array of new XData to the plots via the following syntax. This is only really convenient if you already have your new values in a cell array.
set(plots, {'XData'}, {rand(1,2); rand(1,2)})
The other options is to update each plot object individually with the new values. As far as doing this quickly, there really isn't much of a performance hit by not setting them all at once, because they will not actually be rendered until MATLAB is idle or you explicitly call drawnow.
X = rand(2);
Y = rand(2);
for k = 1:numel(plots)
set(plots(k), 'XData', X(k,:), 'YData', Y(k,:))
end
% Force the rendering *after* you update all data
drawnow
If you really want to use the XDataSource and YDataSource method that you have shown, you can actually do this, but you would need to specify a unique data source for each plot object.
% Do this when you create the plots
for k = 1:numel(plots)
set(plots(k), 'XDataSource', sprintf('X(%d,:)', k), ...
'YDataSource', sprintf('Y(%d,:)', k))
end
% Now update the plot data
X = rand(2);
Y = rand(2);
refreshdata(plots)
You can use drawnow:
%Creation of the vectors
x = 1:100;
y = rand(1,100);
%1st plot
h = plot(x,y);
pause(2);
%update y
y = rand(1,100);
set(h,'YData',y)
%update the plot.
drawnow

How to extract data from figure in matlab?

I have saved different Matlab plots in an unique .fig. The figure is like this:
Now, I would like to introduce a filter in these plots to reduce the noises, but unfortunately I have lost the code that generates these signals.
Is there a way to extract data of each signal in this figure?
I tried this:
open('ttc_delay1000.fig');
h = gcf; %current figure handle
axesObjs = get(h, 'Children'); %axes handles
dataObjs = get(axesObjs, 'Children'); %handles to low-level graphics objects in axes
objTypes = get(dataObjs, 'Type'); %type of low-level graphics object
xdata = get(dataObjs, 'XData'); %data from low-level grahics objects
ydata = get(dataObjs, 'YData');
But I am confused and I don't know if it's the right way to act.
Thanks!
A one-liner for your problem:
data = get(findobj(open('ttc_delay1000.fig'), 'Type','line'), {'XData','YData'});
The steps are there (from the inner calls to the outer calls):
open the file;
look into it for the line series;
return the data.
data{n,1} will contain the XData of the LineSeries number n, wile the data{n,2} will contain the YData of the said LineSeries.
If you want to smooth the lines directly in the figure, the idea is the same:
%//Prepare moving average filter of size N
N = 5;
f = #(x) filter(ones(1,N)/N, 1, x);
%//Smooth out the Y data of the LineSeries
hf = open('ttc_delay1000.fig');
for hl = transpose(findobj(hf,'Type','line'))
set(hl, 'YData', f(get(hl,'YData')));
end;
saveas(hf, 'ttc_delay1000_smooth.fig');