重力加速度的计步算法求讲解

package com.altria.mystep.step; import android.content.Context; import android.hardware.Sensor; import android.hardware.SensorEvent; import android.hardware.SensorEventListener; import android.hardware.SensorManager; /** * 这是一... package com.altria.mystep.step; import android.content.Context; import android.hardware.Sensor; import android.hardware.SensorEvent; import android.hardware.SensorEventListener; import android.hardware.SensorManager; /** * 这是一个实现了信号监听的记步的类 * 这是从谷歌找来的一个记步的算法，看不太懂 * @author Liyachao Date:2015-1-6 * */ public class StepDetector implements SensorEventListener { public static int CURRENT_SETP = 0;//当前步数 public static float SENSITIVITY = 10; // SENSITIVITY灵敏度 public static boolean flag = false;//服务运行标志 private float mLastValues[] = new float[3 * 2]; private float mScale[] = new float[2]; private float mYOffset; private static long end = 0; private static long start = 0; /** * Z后加速度方向 */ 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; /** * 传入上下文的构造函数 * * @param context */ public StepDetector(Context context) { super(); int h = 480; 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))); } //当加速度传感器检测到的数值发生变化时就会调用这个方法 public void onSensorChanged(SensorEvent event) { if (!flag) return; Sensor sensor = event.sensor; synchronized (this) { if (sensor.getType() == Sensor.TYPE_ACCELEROMETER) { float vSum = 0; for (int i = 0; i < 3; i++) { final float v = mYOffset + event.values[i] * mScale[1]; 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 > SENSITIVITY) { boolean isAlmostAsLargeAsPrevious = diff > (mLastDiff[k] * 2 / 3); boolean isPreviousLargeEnough = mLastDiff[k] > (diff / 3); boolean isNotContra = (mLastMatch != 1 - extType); if (isAlmostAsLargeAsPrevious && isPreviousLargeEnough && isNotContra) { end = System.currentTimeMillis(); if (end - start > 500) {// 此时判断为走了一步 CURRENT_SETP++; mLastMatch = extType; start = end; } } else { mLastMatch = -1; } } mLastDiff[k] = diff; } mLastDirections[k] = direction; mLastValues[k] = v; } } } //当传感器的经度发生变化时就会调用这个方法，在这里没有用 public void onAccuracyChanged(Sensor arg0， int arg1) { } }