1 This directory contains a simple python script for visualizing 2 the behavior of the WindowOrientationListener. 3 4 5 PREREQUISITES 6 ------------- 7 8 1. Python 2.6 9 2. numpy 10 3. matplotlib 11 12 13 USAGE 14 ----- 15 16 The tool works by scaping the debug log output from WindowOrientationListener 17 for interesting data and then plotting it. 18 19 1. 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 22 2. 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 27 3. Run "orientationplot.py". 28 29 30 WHAT IT ALL MEANS 31 ----------------- 32 33 The tool displays several time series graphs that plot the output of the 34 WindowOrientationListener. Here you can see the raw accelerometer data, 35 filtered accelerometer data, measured tilt and orientation angle, confidence 36 intervals for the proposed orientation and accelerometer latency. 37 38 Things to look for: 39 40 1. 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 48 2. 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 68 3. 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 74 4. 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 79 5. 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 83 6. 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
