Android/frameworks_base
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Merge "Slight improvement (hopefully) to orientation sensing." into gingerbread

Browse Source
This commit is contained in:
Steve Howard
2010-08-06 14:28:37 -07:00
committed by Android (Google) Code Review
parent 3b0d3d5141 5f531ae6b3
commit 9fbf00cb04
1 changed files with 189 additions and 58 deletions
Download Patch File Download Diff File Expand all files Collapse all files

247
core/java/android/view/WindowOrientationListener.java
View File

@@ -68,7 +68,7 @@ public abstract class WindowOrientationListener {
mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
if (mSensor != null) {
// Create listener only if sensors do exist
mSensorEventListener = new SensorEventListenerImpl();
mSensorEventListener = new SensorEventListenerImpl(this);
}
}
@@ -109,8 +109,35 @@ public abstract class WindowOrientationListener {
}
return -1;
}
class SensorEventListenerImpl implements SensorEventListener {
/**
* This class filters the raw accelerometer data and tries to detect actual changes in
* orientation. This is a very ill-defined problem so there are a lot of tweakable parameters,
* but here's the outline:
*
* - Convert the acceleromter vector from cartesian to spherical coordinates. Since we're
* dealing with rotation of the device, this is the sensible coordinate system to work in. The
* zenith direction is the Z-axis, i.e. the direction the screen is facing. The radial distance
* is referred to as the magnitude below. The elevation angle is referred to as the "tilt"
* below. The azimuth angle is referred to as the "orientation" below (and the azimuth axis is
* the Y-axis). See http://en.wikipedia.org/wiki/Spherical_coordinate_system for reference.
*
* - Low-pass filter the tilt and orientation angles to avoid "twitchy" behavior.
*
* - When the orientation angle reaches a certain threshold, transition to the corresponding
* orientation. These thresholds have some hysteresis built-in to avoid oscillation.
*
* - Use the magnitude to judge the accuracy of the data. Under ideal conditions, the magnitude
* should equal to that of gravity. When it differs significantly, we know the device is under
* external acceleration and we can't trust the data.
*
* - Use the tilt angle to judge the accuracy of orientation data. When the tilt angle is high
* in magnitude, we distrust the orientation data, because when the device is nearly flat, small
* physical movements produce large changes in orientation angle.
*
* Details are explained below.
*/
static class SensorEventListenerImpl implements SensorEventListener {
// We work with all angles in degrees in this class.
private static final float RADIANS_TO_DEGREES = (float) (180 / Math.PI);
@@ -125,54 +152,50 @@ public abstract class WindowOrientationListener {
private static final int ROTATION_90 = 1;
private static final int ROTATION_270 = 2;
// Current orientation state
private int mRotation = ROTATION_0;
// Mapping our internal aliases into actual Surface rotation values
private final int[] SURFACE_ROTATIONS = new int[] {Surface.ROTATION_0, Surface.ROTATION_90,
Surface.ROTATION_270};
private static final int[] SURFACE_ROTATIONS = new int[] {
Surface.ROTATION_0, Surface.ROTATION_90, Surface.ROTATION_270};
// Threshold ranges of orientation angle to transition into other orientation states.
// The first list is for transitions from ROTATION_0, the next for ROTATION_90, etc.
// ROTATE_TO defines the orientation each threshold range transitions to, and must be kept
// in sync with this.
// The thresholds are nearly regular -- we generally transition about the halfway point
// between two states with a swing of 30 degrees for hysteresis. For ROTATION_180,
// however, we enforce stricter thresholds, pushing the thresholds 15 degrees closer to 180.
private final int[][][] THRESHOLDS = new int[][][] {
// We generally transition about the halfway point between two states with a swing of 30
// degrees for hysteresis.
private static final int[][][] THRESHOLDS = new int[][][] {
{{60, 180}, {180, 300}},
{{0, 30}, {195, 315}, {315, 360}},
{{0, 45}, {45, 165}, {330, 360}},
{{0, 30}, {195, 315}, {315, 360}}
};
// See THRESHOLDS
private final int[][] ROTATE_TO = new int[][] {
{ROTATION_270, ROTATION_90},
private static final int[][] ROTATE_TO = new int[][] {
{ROTATION_90, ROTATION_270},
{ROTATION_0, ROTATION_270, ROTATION_0},
{ROTATION_0, ROTATION_90, ROTATION_0}
{ROTATION_0, ROTATION_90, ROTATION_0},
};
// Maximum absolute tilt angle at which to consider orientation changes. Beyond this (i.e.
// when screen is facing the sky or ground), we refuse to make any orientation changes.
private static final int MAX_TILT = 65;
// Maximum absolute tilt angle at which to consider orientation data. Beyond this (i.e.
// when screen is facing the sky or ground), we completely ignore orientation data.
private static final int MAX_TILT = 75;
// Additional limits on tilt angle to transition to each new orientation. We ignore all
// vectors with tilt beyond MAX_TILT, but we can set stricter limits on transition to a
// data with tilt beyond MAX_TILT, but we can set stricter limits on transitions to a
// particular orientation here.
private final int[] MAX_TRANSITION_TILT = new int[] {MAX_TILT, MAX_TILT, MAX_TILT};
private static final int[] MAX_TRANSITION_TILT = new int[] {MAX_TILT, 65, 65};
// Between this tilt angle and MAX_TILT, we'll allow orientation changes, but we'll filter
// with a higher time constant, making us less sensitive to change. This primarily helps
// prevent momentary orientation changes when placing a device on a table from the side (or
// picking one up).
private static final int PARTIAL_TILT = 45;
private static final int PARTIAL_TILT = 50;
// Maximum allowable deviation of the magnitude of the sensor vector from that of gravity,
// in m/s^2. Beyond this, we assume the phone is under external forces and we can't trust
// the sensor data. However, under constantly vibrating conditions (think car mount), we
// still want to pick up changes, so rather than ignore the data, we filter it with a very
// high time constant.
private static final int MAX_DEVIATION_FROM_GRAVITY = 1;
private static final float MAX_DEVIATION_FROM_GRAVITY = 1.5f;
// Actual sampling period corresponding to SensorManager.SENSOR_DELAY_NORMAL. There's no
// way to get this information from SensorManager.
@@ -185,28 +208,46 @@ public abstract class WindowOrientationListener {
// background.
// When device is near-vertical (screen approximately facing the horizon)
private static final int DEFAULT_TIME_CONSTANT_MS = 200;
private static final int DEFAULT_TIME_CONSTANT_MS = 50;
// When device is partially tilted towards the sky or ground
private static final int TILTED_TIME_CONSTANT_MS = 600;
private static final int TILTED_TIME_CONSTANT_MS = 300;
// When device is under external acceleration, i.e. not just gravity. We heavily distrust
// such readings.
private static final int ACCELERATING_TIME_CONSTANT_MS = 5000;
private static final int ACCELERATING_TIME_CONSTANT_MS = 2000;
private static final float DEFAULT_LOWPASS_ALPHA =
(float) SAMPLING_PERIOD_MS / (DEFAULT_TIME_CONSTANT_MS + SAMPLING_PERIOD_MS);
computeLowpassAlpha(DEFAULT_TIME_CONSTANT_MS);
private static final float TILTED_LOWPASS_ALPHA =
(float) SAMPLING_PERIOD_MS / (TILTED_TIME_CONSTANT_MS + SAMPLING_PERIOD_MS);
computeLowpassAlpha(TILTED_TIME_CONSTANT_MS);
private static final float ACCELERATING_LOWPASS_ALPHA =
(float) SAMPLING_PERIOD_MS / (ACCELERATING_TIME_CONSTANT_MS + SAMPLING_PERIOD_MS);
computeLowpassAlpha(ACCELERATING_TIME_CONSTANT_MS);
// The low-pass filtered accelerometer data
private float[] mFilteredVector = new float[] {0, 0, 0};
private WindowOrientationListener mOrientationListener;
private int mRotation = ROTATION_0; // Current orientation state
private float mTiltAngle = 0; // low-pass filtered
private float mOrientationAngle = 0; // low-pass filtered
/*
* Each "distrust" counter represents our current level of distrust in the data based on
* a certain signal. For each data point that is deemed unreliable based on that signal,
* the counter increases; otherwise, the counter decreases. Exact rules vary.
*/
private int mAccelerationDistrust = 0; // based on magnitude != gravity
private int mTiltDistrust = 0; // based on tilt close to +/- 90 degrees
public SensorEventListenerImpl(WindowOrientationListener orientationListener) {
mOrientationListener = orientationListener;
}
private static float computeLowpassAlpha(int timeConstantMs) {
return (float) SAMPLING_PERIOD_MS / (timeConstantMs + SAMPLING_PERIOD_MS);
}
int getCurrentRotation() {
return SURFACE_ROTATIONS[mRotation];
}
private void calculateNewRotation(int orientation, int tiltAngle) {
private void calculateNewRotation(float orientation, float tiltAngle) {
if (localLOGV) Log.i(TAG, orientation + ", " + tiltAngle + ", " + mRotation);
int thresholdRanges[][] = THRESHOLDS[mRotation];
int row = -1;
@@ -226,7 +267,7 @@ public abstract class WindowOrientationListener {
if (localLOGV) Log.i(TAG, " new rotation = " + rotation);
mRotation = rotation;
onOrientationChanged(SURFACE_ROTATIONS[rotation]);
mOrientationListener.onOrientationChanged(getCurrentRotation());
}
private float lowpassFilter(float newValue, float oldValue, float alpha) {
@@ -238,11 +279,11 @@ public abstract class WindowOrientationListener {
}
/**
* Absolute angle between upVector and the x-y plane (the plane of the screen), in [0, 90].
* 90 degrees = screen facing the sky or ground.
* Angle between upVector and the x-y plane (the plane of the screen), in [-90, 90].
* +/- 90 degrees = screen facing the sky or ground.
*/
private float tiltAngle(float z, float magnitude) {
return Math.abs((float) Math.asin(z / magnitude) * RADIANS_TO_DEGREES);
return (float) Math.asin(z / magnitude) * RADIANS_TO_DEGREES;
}
public void onSensorChanged(SensorEvent event) {
@@ -253,34 +294,124 @@ public abstract class WindowOrientationListener {
float z = event.values[_DATA_Z];
float magnitude = vectorMagnitude(x, y, z);
float deviation = Math.abs(magnitude - SensorManager.STANDARD_GRAVITY);
float tiltAngle = tiltAngle(z, magnitude);
float alpha = DEFAULT_LOWPASS_ALPHA;
if (tiltAngle > MAX_TILT) {
return;
} else if (deviation > MAX_DEVIATION_FROM_GRAVITY) {
handleAccelerationDistrust(deviation);
// only filter tilt when we're accelerating
float alpha = 1;
if (mAccelerationDistrust > 0) {
alpha = ACCELERATING_LOWPASS_ALPHA;
} else if (tiltAngle > PARTIAL_TILT) {
}
float newTiltAngle = tiltAngle(z, magnitude);
mTiltAngle = lowpassFilter(newTiltAngle, mTiltAngle, alpha);
float absoluteTilt = Math.abs(mTiltAngle);
if (checkFullyTilted(absoluteTilt)) {
return; // when fully tilted, ignore orientation entirely
}
float newOrientationAngle = computeNewOrientation(x, y);
filterOrientation(absoluteTilt, newOrientationAngle);
calculateNewRotation(mOrientationAngle, absoluteTilt);
}
/**
* When accelerating, increment distrust; otherwise, decrement distrust. The idea is that
* if a single jolt happens among otherwise good data, we should keep trusting the good
* data. On the other hand, if a series of many bad readings comes in (as if the phone is
* being rapidly shaken), we should wait until things "settle down", i.e. we get a string
* of good readings.
*
* @param deviation absolute difference between the current magnitude and gravity
*/
private void handleAccelerationDistrust(float deviation) {
if (deviation > MAX_DEVIATION_FROM_GRAVITY) {
if (mAccelerationDistrust < 5) {
mAccelerationDistrust++;
}
} else if (mAccelerationDistrust > 0) {
mAccelerationDistrust--;
}
}
/**
* Check if the phone is tilted towards the sky or ground and handle that appropriately.
* When fully tilted, we automatically push the tilt up to a fixed value; otherwise we
* decrement it. The idea is to distrust the first few readings after the phone gets
* un-tilted, no matter what, i.e. preventing an accidental transition when the phone is
* picked up from a table.
*
* We also reset the orientation angle to the center of the current screen orientation.
* Since there is no real orientation of the phone, we want to ignore the most recent sensor
* data and reset it to this value to avoid a premature transition when the phone starts to
* get un-tilted.
*
* @param absoluteTilt the absolute value of the current tilt angle
* @return true if the phone is fully tilted
*/
private boolean checkFullyTilted(float absoluteTilt) {
boolean fullyTilted = absoluteTilt > MAX_TILT;
if (fullyTilted) {
if (mRotation == ROTATION_0) {
mOrientationAngle = 0;
} else if (mRotation == ROTATION_90) {
mOrientationAngle = 90;
} else { // ROTATION_270
mOrientationAngle = 270;
}
if (mTiltDistrust < 3) {
mTiltDistrust = 3;
}
} else if (mTiltDistrust > 0) {
mTiltDistrust--;
}
return fullyTilted;
}
/**
* Angle between the x-y projection of upVector and the +y-axis, increasing
* clockwise.
* 0 degrees = speaker end towards the sky
* 90 degrees = right edge of device towards the sky
*/
private float computeNewOrientation(float x, float y) {
float orientationAngle = (float) -Math.atan2(-x, y) * RADIANS_TO_DEGREES;
// atan2 returns [-180, 180]; normalize to [0, 360]
if (orientationAngle < 0) {
orientationAngle += 360;
}
return orientationAngle;
}
/**
* Compute a new filtered orientation angle.
*/
private void filterOrientation(float absoluteTilt, float orientationAngle) {
float alpha = DEFAULT_LOWPASS_ALPHA;
if (mTiltDistrust > 0 || mAccelerationDistrust > 1) {
// when fully tilted, or under more than a transient acceleration, distrust heavily
alpha = ACCELERATING_LOWPASS_ALPHA;
} else if (absoluteTilt > PARTIAL_TILT || mAccelerationDistrust == 1) {
// when tilted partway, or under transient acceleration, distrust lightly
alpha = TILTED_LOWPASS_ALPHA;
}
x = mFilteredVector[0] = lowpassFilter(x, mFilteredVector[0], alpha);
y = mFilteredVector[1] = lowpassFilter(y, mFilteredVector[1], alpha);
z = mFilteredVector[2] = lowpassFilter(z, mFilteredVector[2], alpha);
magnitude = vectorMagnitude(x, y, z);
tiltAngle = tiltAngle(z, magnitude);
// Angle between the x-y projection of upVector and the +y-axis, increasing
// counter-clockwise.
// 0 degrees = speaker end towards the sky
// 90 degrees = left edge of device towards the sky
float orientationAngle = (float) Math.atan2(-x, y) * RADIANS_TO_DEGREES;
int orientation = Math.round(orientationAngle);
// atan2 returns (-180, 180]; normalize to [0, 360)
if (orientation < 0) {
orientation += 360;
// since we're lowpass filtering a value with periodic boundary conditions, we need to
// adjust the new value to filter in the right direction...
float deltaOrientation = orientationAngle - mOrientationAngle;
if (deltaOrientation > 180) {
orientationAngle -= 360;
} else if (deltaOrientation < -180) {
orientationAngle += 360;
}
mOrientationAngle = lowpassFilter(orientationAngle, mOrientationAngle, alpha);
// ...and then adjust back to ensure we're in the range [0, 360]
if (mOrientationAngle > 360) {
mOrientationAngle -= 360;
} else if (mOrientationAngle < 0) {
mOrientationAngle += 360;
}
calculateNewRotation(orientation, Math.round(tiltAngle));
}
public void onAccuracyChanged(Sensor sensor, int accuracy) {