一起来讨论下这个计步器的算法

fat2213fdf 2015-03-14 08:55:46

源地址：https://github.com/bagilevi/android-pedometer/blob/master/src/name/bagi/levente/pedometer/StepDetector.java
实在是看不懂。。。为什么还用到了MAGNETIC_FIELD_EARTH_MAX？
参考资料：http://developer.android.com/reference/android/hardware/SensorManager.html



/*

 *  Pedometer - Android App

 *  Copyright (C) 2009 Levente Bagi

 *

 *  This program is free software: you can redistribute it and/or modify

 *  it under the terms of the GNU General Public License as published by

 *  the Free Software Foundation, either version 3 of the License, or

 *  (at your option) any later version.

 *

 *  This program is distributed in the hope that it will be useful,

 *  but WITHOUT ANY WARRANTY; without even the implied warranty of

 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 *  GNU General Public License for more details.

 *

 *  You should have received a copy of the GNU General Public License

 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.

 */



package name.bagi.levente.pedometer;



import java.util.ArrayList;



import android.hardware.Sensor;

import android.hardware.SensorEvent;

import android.hardware.SensorEventListener;

import android.hardware.SensorManager;

import android.util.Log;



/**

 * Detects steps and notifies all listeners (that implement StepListener).

 * @author Levente Bagi

 * @todo REFACTOR: SensorListener is deprecated

 */

public class StepDetector implements SensorEventListener

{

    private final static String TAG = "StepDetector";

    private float   mLimit = 10;

    private float   mLastValues[] = new float[3*2];

    private float   mScale[] = new float[2];

    private float   mYOffset;



    private float   mLastDirections[] = new float[3*2];

    private float   mLastExtremes[][] = { new float[3*2], new float[3*2] };

    private float   mLastDiff[] = new float[3*2];

    private int     mLastMatch = -1;

    

    private ArrayList<StepListener> mStepListeners = new ArrayList<StepListener>();

    

    public StepDetector() {

        int h = 480; // TODO: remove this constant

        mYOffset = h * 0.5f;

        mScale[0] = - (h * 0.5f * (1.0f / (SensorManager.STANDARD_GRAVITY * 2)));

        mScale[1] = - (h * 0.5f * (1.0f / (SensorManager.MAGNETIC_FIELD_EARTH_MAX)));

    }

    

    public void setSensitivity(float sensitivity) {

        mLimit = sensitivity; // 1.97  2.96  4.44  6.66  10.00  15.00  22.50  33.75  50.62

    }

    

    public void addStepListener(StepListener sl) {

        mStepListeners.add(sl);

    }

    

    //public void onSensorChanged(int sensor, float[] values) {

    public void onSensorChanged(SensorEvent event) {

        Sensor sensor = event.sensor; 

        synchronized (this) {

            if (sensor.getType() == Sensor.TYPE_ORIENTATION) {

            }

            else {

                int j = (sensor.getType() == Sensor.TYPE_ACCELEROMETER) ? 1 : 0;

                if (j == 1) {

                    float vSum = 0;

                    for (int i=0 ; i<3 ; i++) {

                        final float v = mYOffset + event.values[i] * mScale[j];

                        vSum += v;

                    }

                    int k = 0;

                    float v = vSum / 3;

                    

                    float direction = (v > mLastValues[k] ? 1 : (v < mLastValues[k] ? -1 : 0));

                    if (direction == - mLastDirections[k]) {

                        // Direction changed

                        int extType = (direction > 0 ? 0 : 1); // minumum or maximum?

                        mLastExtremes[extType][k] = mLastValues[k];

                        float diff = Math.abs(mLastExtremes[extType][k] - mLastExtremes[1 - extType][k]);



                        if (diff > mLimit) {

                            

                            boolean isAlmostAsLargeAsPrevious = diff > (mLastDiff[k]*2/3);

                            boolean isPreviousLargeEnough = mLastDiff[k] > (diff/3);

                            boolean isNotContra = (mLastMatch != 1 - extType);

                            

                            if (isAlmostAsLargeAsPrevious && isPreviousLargeEnough && isNotContra) {

                                Log.i(TAG, "step");

                                for (StepListener stepListener : mStepListeners) {

                                    stepListener.onStep();

                                }

                                mLastMatch = extType;

                            }

                            else {

                                mLastMatch = -1;

                            }

                        }

                        mLastDiff[k] = diff;

                    }

                    mLastDirections[k] = direction;

                    mLastValues[k] = v;

                }

            }

        }

    }

    

    public void onAccuracyChanged(Sensor sensor, int accuracy) {

        // TODO Auto-generated method stub

    }



}