Decreasing the lag on the Android Matlab app sensor data .

Hi,I am a total newbie to matlab. I been trying to get sensor data from my android phone. I am getting the data but there is almost a lag of 1 second. here is my code

clear all
close all
clc

connector on;

m = mobiledev();
m.OrientationSensor = 1;
m.Logging = 1;
pause (4)

for c = 1:inf

       o = m.Orientation
       pause(0.1);

       figure(1);
       axis tight
       hold on  
       plot(c,o(1),'.');

       figure(2);
       axis tight
       hold on  
       plot(c,o(2),'.');

       figure(3);
       axis tight
       hold on  
       plot(c,o(3),'.');

end

Answer 1

[Walter Roberson]

Your graphics is inefficient and is going to get worse as you increase the number of readings.

for K = 1 : 3
  figs(K) = figure(K);
  figax(K) = axes('Parent', figs(K));
  axis(figax(K),'tight');
  pline(K) = plot(figax(K), [], [], '.');   %exists but empty
end
drawnow();

crecord = zeros(4, 512); %pre-allocate for 512 points 

for c = 1:inf
  o = m.Orientation;
  if c > size(crecord,2)
    crecord(4,c+255) = 0;  %grow the record if it is getting small
  end
  crecord(4,c) = c;        %remember observation number
  for K = 1 : 3            
    crecord(K, c) = o(K);  %copy the current data into the record
    set(pline(K),'xdata', crecord(4,1:c), 'ydata', crecord(K,1:c)); %update line
  end
  drawnow();   %repaint screen
end

[Walter Roberson]

It appears to me that as you are not using Logging, each time you ask for the Orientation, MATLAB sends a command to Android to request the data and Android sends back a response. That introduces latency. You can reduce the latency by turning on Logging, in which case the Android will send a stream of readings to MATLAB. For an example, see http://www.mathworks.com/help/supportpkg/mobilesensor/ug/use-logged-sensor-data.html

Answer 2

[kalvik jakkala]

Ok so where dose the plot command go?? And I don't think the problem is the code. I mean it's not good but when i enter o = m.Orientation on the command window while moving my phone it takes a while get the latest values. There is a lag of about 1 sec. I was wondering if it is possible to get the data via a usb cable instead of wifi.

[Walter Roberson]

The plot command goes right where I show it, in the loop that builds the figures and associated axes. After that, you do not call plot(): instead you use set() to update the XData and YData properties of the line() objects that were created by the plot() calls. Updating the XData and YData properties so that they have all of the data points will result in faster graphics than having one line() object for every point.