README.txt
1This directory contains a simple python script for visualizing
2the behavior of the WindowOrientationListener.
3
4
5PREREQUISITES
6-------------
7
81. Python 2.6
92. numpy
103. matplotlib
11
12
13USAGE
14-----
15
16The tool works by scaping the debug log output from WindowOrientationListener
17for interesting data and then plotting it.
18
191. Plug in the device. Ensure that it is the only device plugged in
20 since this script is of very little brain and will get confused otherwise.
21
222. Enable the Window Orientation Listener debugging data log.
23 adb shell setprop debug.orientation.log true
24 adb shell stop
25 adb shell start
26
273. Run "orientationplot.py".
28
29
30WHAT IT ALL MEANS
31-----------------
32
33The tool displays several time series graphs that plot the output of the
34WindowOrientationListener. Here you can see the raw accelerometer data,
35filtered accelerometer data, measured tilt and orientation angle, confidence
36intervals for the proposed orientation and accelerometer latency.
37
38Things to look for:
39
401. Ensure the filtering is not too aggressive. If the filter cut-off frequency is
41 less than about 1Hz, then the filtered accelorometer data becomes too smooth
42 and the latency for orientation detection goes up. One way to observe this
43 is by holding the device vertically in one orientation then sharply turning
44 it 90 degrees to a different orientation. Compared the rapid changes in the
45 raw accelerometer data with the smoothed out filtered data. If the filtering
46 is too aggressive, the filter response may lag by hundreds of milliseconds.
47
482. Ensure that there is an appropriate gap between adjacent orientation angles
49 for hysteresis. Try holding the device in one orientation and slowly turning
50 it 90 degrees. Note that the confidence intervals will all drop to 0 at some
51 point in between the two orientations; that is the gap. The gap should be
52 observed between all adjacent pairs of orientations when turning the device
53 in either direction.
54
55 Next try holding the device in one orientation and rapidly turning it end
56 over end to a midpoint about 45 degrees between two opposing orientations.
57 There should be no gap observed initially. The algorithm should pick one
58 of the orientations and settle into it (since it is obviously quite
59 different from the original orientation of the device). However, once it
60 settles, the confidence values should start trending to 0 again because
61 the measured orientation angle is now within the gap between the new
62 orientation and the adjacent orientation.
63
64 In other words, the hysteresis gap applies only when the measured orientation
65 angle (say, 45 degrees) is between the current orientation's ideal angle
66 (say, 0 degrees) and an adjacent orientation's ideal angle (say, 90 degrees).
67
683. Accelerometer jitter. The accelerometer latency graph displays the interval
69 between sensor events as reported by the SensorEvent.timestamp field. It
70 should be a fairly constant 60ms. If the latency jumps around wildly or
71 greatly exceeds 60ms then there is a problem with the accelerometer or the
72 sensor manager.
73
744. The orientation angle is not measured when the tilt is too close to 90 or -90
75 degrees (refer to MAX_TILT constant). Consequently, you should expect there
76 to be no data. Likewise, all dependent calculations are suppressed in this case
77 so there will be no orientation proposal either.
78
795. Each orientation has its own bound on allowable tilt angles. It's a good idea to
80 verify that these limits are being enforced by gradually varying the tilt of
81 the device until it is inside/outside the limit for each orientation.
82
836. Orientation changes should be significantly harder when the device is held
84 overhead. People reading on tablets in bed often have their head turned
85 a little to the side, or they hold the device loosely so its orientation
86 can be a bit unusual. The tilt is a good indicator of whether the device is
87 overhead.
88