问题
In my app i wanted to show device direction such as north, south, east, west. For that i am using accelerometer and magnetic sensor and tried with following code.
public class MainActivity extends Activity implements SensorEventListener
{
public static float swRoll;
public static float swPitch;
public static float swAzimuth;
public static SensorManager mSensorManager;
public static Sensor accelerometer;
public static Sensor magnetometer;
public static float[] mAccelerometer = null;
public static float[] mGeomagnetic = null;
public void onAccuracyChanged(Sensor sensor, int accuracy) {
}
@Override
public void onSensorChanged(SensorEvent event)
{
// onSensorChanged gets called for each sensor so we have to remember the values
if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER)
{
mAccelerometer = event.values;
}
if (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD)
{
mGeomagnetic = event.values;
}
if (mAccelerometer != null && mGeomagnetic != null)
{
float R[] = new float[9];
float I[] = new float[9];
boolean success = SensorManager.getRotationMatrix(R, I, mAccelerometer, mGeomagnetic);
if (success)
{
float orientation[] = new float[3];
SensorManager.getOrientation(R, orientation);
// at this point, orientation contains the azimuth(direction), pitch and roll values.
double azimuth = 180 * orientation[0] / Math.PI;
//double pitch = 180 * orientation[1] / Math.PI;
//double roll = 180 * orientation[2] / Math.PI;
Toast.makeText(getApplicationContext(), "azimuth: "+azimuth, Toast.LENGTH_SHORT).show();
//Toast.makeText(getApplicationContext(), "pitch: "+pitch, Toast.LENGTH_SHORT).show();
//Toast.makeText(getApplicationContext(), "roll: "+roll, Toast.LENGTH_SHORT).show();
}
}
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mSensorManager = (SensorManager)getSystemService(SENSOR_SERVICE);
accelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
magnetometer = mSensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);
}
@Override
protected void onResume() {
super.onResume();
mSensorManager.registerListener(this, accelerometer, SensorManager.SENSOR_DELAY_GAME);
mSensorManager.registerListener(this, magnetometer, SensorManager.SENSOR_DELAY_GAME);
}
@Override
protected void onPause() {
super.onPause();
mSensorManager.unregisterListener(this, accelerometer);
mSensorManager.unregisterListener(this, magnetometer);
}
}
I read some artical and come to know that azimuth value is use for getting direction. But it not shows proper value i.e it always shows value between 103 to 140 in any direction. I am using samsung galaxy s for test purpose. where i goes wrong. Any help will be appreciated...thank you
回答1:
EDIT: I'm going to keep this answer up because there are no other answers here, but my gut feeling looking at this code again is it probably doesn't work well. Use at your own risk, and if anyone ever gives a decent answer I'll delete this
Here's a compass sensor I wrote for my own use. It works, somewhat. In reality it needs better filtering- the results from the sensor are very noisy, I built a filter on top of it to slow the updates and it improved things, but it needs a much better filter if it was to be used in production
package com.gabesechan.android.reusable.sensor;
import java.lang.ref.WeakReference;
import java.util.HashSet;
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Handler;
import android.os.Message;
public class CompassSensor {
SensorManager sm;
int lastDirection = -1;
int lastPitch;
int lastRoll;
boolean firstReading = true;
HashSet<CompassListener> listeners = new HashSet<CompassListener>();
static CompassSensor mInstance;
public static CompassSensor getInstance(Context ctx){
if(mInstance == null){
mInstance = new CompassSensor(ctx);
}
return mInstance;
}
private CompassSensor(Context ctx){
sm = (SensorManager) ctx.getSystemService(Context.SENSOR_SERVICE);
onResume();
}
public void onResume(){
sm.registerListener(sensorListener, sm.getDefaultSensor(Sensor.TYPE_ACCELEROMETER), SensorManager.SENSOR_DELAY_NORMAL);
sm.registerListener(sensorListener, sm.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD), SensorManager.SENSOR_DELAY_UI);
firstReading = true;
//Restart the timer only if we have listeners
if(listeners.size()>0){
handler.sendMessageDelayed(Message.obtain(handler, 1),1000);
}
}
public void onPause(){
sm.unregisterListener(sensorListener);
handler.removeMessages(1);
}
private final SensorEventListener sensorListener = new SensorEventListener(){
float accelerometerValues[] = null;
float geomagneticMatrix[] = null;
public void onSensorChanged(SensorEvent event) {
if (event.accuracy == SensorManager.SENSOR_STATUS_UNRELIABLE)
return;
switch (event.sensor.getType()) {
case Sensor.TYPE_ACCELEROMETER:
accelerometerValues = event.values.clone();
break;
case Sensor.TYPE_MAGNETIC_FIELD:
geomagneticMatrix = event.values.clone();
break;
}
if (geomagneticMatrix != null && accelerometerValues != null && event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD) {
float[] R = new float[16];
float[] I = new float[16];
float[] outR = new float[16];
//Get the rotation matrix, then remap it from camera surface to world coordinates
SensorManager.getRotationMatrix(R, I, accelerometerValues, geomagneticMatrix);
SensorManager.remapCoordinateSystem(R, SensorManager.AXIS_X, SensorManager.AXIS_Z, outR);
float values[] = new float[4];
SensorManager.getOrientation(outR,values);
int direction = normalizeDegrees(filterChange((int)Math.toDegrees(values[0])));
int pitch = normalizeDegrees(Math.toDegrees(values[1]));
int roll = normalizeDegrees(Math.toDegrees(values[2]));
if((int)direction != (int)lastDirection){
lastDirection = (int)direction;
lastPitch = (int)pitch;
lastRoll = (int)roll;
}
}
}
public void onAccuracyChanged(Sensor sensor, int accuracy) {
}
};
//Normalize a degree from 0 to 360 instead of -180 to 180
private int normalizeDegrees(double rads){
return (int)((rads+360)%360);
}
//We want to ignore large bumps in individual readings. So we're going to cap the number of degrees we can change per report
private static final int MAX_CHANGE = 3;
private int filterChange(int newDir){
newDir = normalizeDegrees(newDir);
//On the first reading, assume it's right. Otherwise NW readings take forever to ramp up
if(firstReading){
firstReading = false;
return newDir;
}
//Figure out how many degrees to move
int delta = newDir - lastDirection;
int normalizedDelta = normalizeDegrees(delta);
int change = Math.min(Math.abs(delta),MAX_CHANGE);
//We always want to move in the direction of lower distance. So if newDir is lower and delta is less than half a circle, lower lastDir
// Same if newDir is higher but the delta is more than half a circle (you'd be faster in the other direction going lower).
if( normalizedDelta > 180 ){
change = -change;
}
return lastDirection+change;
}
public void addListener(CompassListener listener){
if(listeners.size() == 0){
//Start the timer on first listener
handler.sendMessageDelayed(Message.obtain(handler, 1),1000);
}
listeners.add(listener);
}
public void removeListener(CompassListener listener){
listeners.remove(listener);
if(listeners.size() == 0){
handler.removeMessages(1);
}
}
public int getLastDirection(){
return lastDirection;
}
public int getLastPitch(){
return lastPitch;
}
public int getLastRoll(){
return lastPitch;
}
private void callListeners(){
for(CompassListener listener: listeners){
listener.onDirectionChanged(lastDirection, lastPitch, lastRoll);
}
}
//This handler is run every 1s, and updates the listeners
//Static class because otherwise we leak, Eclipse told me so
static class IncomingHandler extends Handler {
private final WeakReference<CompassSensor> compassSensor;
IncomingHandler(CompassSensor sensor) {
compassSensor = new WeakReference<CompassSensor>(sensor);
}
@Override
public void handleMessage(Message msg)
{
CompassSensor sensor = compassSensor.get();
if (sensor != null) {
sensor.callListeners();
}
sendMessageDelayed(Message.obtain(this, 1), 1000);
}
}
IncomingHandler handler = new IncomingHandler(this);
public interface CompassListener {
void onDirectionChanged(int direction, int pitch, int roll);
}
}
来源：https://stackoverflow.com/questions/14433182/direction-using-sensor