how can I move a Point in a plot (GUI) from one side to the other in a fixed time?

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I have a point in a plot and I want to move it "smoothly" to the other side of the plot within a fixed amount of time. In the example this time is 3s, and I refresh the plot "every 20ms" (20ms is what I want, but it's always more, between: 30 and 50ms). My code is:
interval=3000/20; %3000/20=150
for i=1:1:interval
set(pointHandle,'Xdata',point(1).coordinatesNow(1)+(500/150),'Ydata',point(1).coordinatesNow(2)); %Only refresh Xaxis
pause(0.02); %pause of 20ms
a=a+etime(clock,iTime); %total elapsed time
disp(a); %show total time
So I'd like "a" to be 3s, but most of the times is between 7 and 10s, How could I get more accuracy?

Accepted Answer

Robert Cumming
Robert Cumming on 19 Oct 2014
Edited: Robert Cumming on 20 Oct 2014
edit: changed timing to an overall target for loop instead of interval time.
See the code below:
ax = axes;
x = [0:100];
h = plot ( ax, x, x*0 );
ax.YLim = [0 100];
targetTime = 3;
nSteps = 100;
intervalTime = targetTime./nSteps;
loop = tic;
for ii=1:nSteps
h.YData(:) = ii;
timeTaken = toc(loop);
% comment out this line to see the effet of the pause
When I run this in matlab I get the following:
Elapsed time is 1.174296 seconds. (pause commented out)
Elapsed time is 3.006906 seconds.
Robert Cumming
Robert Cumming on 20 Oct 2014
Edited: Robert Cumming on 20 Oct 2014
There will be a small overhead of calculating the input to the pause function and for the loop itself.
You could test what that value is (around .5 from your figures above) and modify your eachLoopTarget variable accordingly.
edit I have changed my example code to target a total time rather than a explicit interval time.

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More Answers (2)

Image Analyst
Image Analyst on 18 Oct 2014
What happens to the time if you reduce the .02 to something less?
Óscar on 18 Oct 2014
Thank you, I don't really need it to be 3.000 seconds, it can be 2.9 or 3.1, but the things is that 3s it's only an example the user we'll have to select it, and he'll be able to choose whichever time he wants... now it's only for 1 point, but there are going to be up to ten points... so I'm just wondering which is the best choice to get a time as accurate as possible.

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Robert Cumming
Robert Cumming on 18 Oct 2014
You need to work out how long it takes to update the plot, then adjust your pause command to suit at runtime so that the code runs at the speed you want it to.
Robert Cumming
Robert Cumming on 19 Oct 2014
I dont know wwhy you think pause will take longer, this time it would have no plot refresh so it should pause for the requested time.
See my other answer for an example code (I didn't edit this one as I answered it with an old account that I no longer use....)

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