过滤加速度计数据的噪声(Filtering accelerometer data noise)

如何过滤在Android上的加速度计数据的噪音？我想为我的样本数据创建一个高通滤波器，这样我就可以消除低频分量，并专注于高频成分。我已阅读，卡尔曼滤波可能是我们的最佳人选，但如何整合或使用我的应用程序这种方法，将主要写的Android的Java？或者可以将它摆在首位做些什么呢？，或利用Android NDK？是否有任何机会，这可以实时完成？

任何想法将非常感激。谢谢！

Answer 1:

从苹果公司的SDK样品实际实现滤波，它是利用斜坡的更简单的方法：

//ramp-speed - play with this value until satisfied
const float kFilteringFactor = 0.1f;

//last result storage - keep definition outside of this function, eg. in wrapping object
float accel[3]; 

//acceleration.x,.y,.z is the input from the sensor

//result.x,.y,.z is the filtered result

//high-pass filter to eliminate gravity
accel[0] = acceleration.x * kFilteringFactor + accel[0] * (1.0f - kFilteringFactor);
accel[1] = acceleration.y * kFilteringFactor + accel[1] * (1.0f - kFilteringFactor);
accel[2] = acceleration.z * kFilteringFactor + accel[2] * (1.0f - kFilteringFactor);
result.x = acceleration.x - accel[0];
result.y = acceleration.y - accel[1];
result.z = acceleration.z - accel[2];

Answer 2:

下面是适用于Android的代码，改编自苹果自适应高通滤波器的例子。只需插入这个和实施onFilteredAccelerometerChanged（）

private static final boolean ADAPTIVE_ACCEL_FILTER = true;
float lastAccel[] = new float[3];
float accelFilter[] = new float[3];

public void onAccelerometerChanged(float accelX, float accelY, float accelZ) {
    // high pass filter
    float updateFreq = 30; // match this to your update speed
    float cutOffFreq = 0.9f;
    float RC = 1.0f / cutOffFreq;
    float dt = 1.0f / updateFreq;
    float filterConstant = RC / (dt + RC);
    float alpha = filterConstant; 
    float kAccelerometerMinStep = 0.033f;
    float kAccelerometerNoiseAttenuation = 3.0f;

    if(ADAPTIVE_ACCEL_FILTER)
    {
        float d = clamp(Math.abs(norm(accelFilter[0], accelFilter[1], accelFilter[2]) - norm(accelX, accelY, accelZ)) / kAccelerometerMinStep - 1.0f, 0.0f, 1.0f);
        alpha = d * filterConstant / kAccelerometerNoiseAttenuation + (1.0f - d) * filterConstant;
    }

    accelFilter[0] = (float) (alpha * (accelFilter[0] + accelX - lastAccel[0]));
    accelFilter[1] = (float) (alpha * (accelFilter[1] + accelY - lastAccel[1]));
    accelFilter[2] = (float) (alpha * (accelFilter[2] + accelZ - lastAccel[2]));

    lastAccel[0] = accelX;
    lastAccel[1] = accelY;
    lastAccel[2] = accelZ;
    onFilteredAccelerometerChanged(accelFilter[0], accelFilter[1], accelFilter[2]);
}

Answer 3:

：对于那些想知道什么规范（）和钳位（）方法从rbgrn答案做，你可以看到他们在这里~~http://developer.apple.com/library/IOS/samplecode/AccelerometerGraph/Listings/AccelerometerGraph_AccelerometerFilter_m.html~~

double norm(double x, double y, double z)
{
    return Math.sqrt(x * x + y * y + z * z);
}

double clamp(double v, double min, double max)
{
    if(v > max)
        return max;
    else if(v < min)
        return min;
    else
        return v;
}