iOS：根据加速度计输出准确确定碰撞能量

我正在创建一个音叉应用程序，您可以将 iPhone 轻拍到另一只手的手掌上，或者轻拍到柔软的表面上，以设置音叉的声音。

所以我想检测每个“凹凸”中包含的能量

（编辑：删除了大量的gumpf）

谁能帮我破解这个吗？

感谢 freenode 的 #math 频道上的一位向导（感谢 Igor），我有了一个非常好的工作解决方案。

您使用标准方法以可能的最大频率 (100Hz) 触发回调，其中将包含瞬时加速度 x、y、z 值。

我会让代码自己说话，好的代码应该总是自己说话。

typedef 
struct {
    double x,y,z;
}
vec_d3;

#define RECENT_COUNT 10

#define SMOOTH_IP( x, x_new, fac )  x  =  fac * x  +  ( 1. - fac ) * x_new

- (void) accelerometer: (UIAccelerometer *) accelerometer 
          didAccelerate: (UIAcceleration *) acceleration 
{
    // smooth incoming acceleration values
    static vec_d3 smooth = { DOUBLE_EMPTY, 0, 0 };

    {
        if ( smooth.x == DOUBLE_EMPTY )
        {
            smooth.x = acceleration.x;
            smooth.y = acceleration.y;
            smooth.z = acceleration.z;

            return;
        }

        SMOOTH_IP( smooth.x, acceleration.x, 0.9 );
        SMOOTH_IP( smooth.y, acceleration.y, 0.9 );
        SMOOTH_IP( smooth.z, acceleration.z, 0.9 );
    }

    // keep track of last k smoothed acceleration values
    static vec_d3 recent[ RECENT_COUNT ];
    {
        static int ptr = 0;
        static BOOL gotEnoughData = NO;

        recent[ ptr ] = smooth;

        ptr++;
        if ( ptr == RECENT_COUNT )
        {
            ptr = 0;
            gotEnoughData = YES;
        }

        // return if array not filled yet
        if ( ! gotEnoughData )
            return;
    }

    // get the resultant variation in acceleration over the whole array
    double variation;
    {
        vec_d3 min = smooth, max = smooth;

        for ( int i=0; i < RECENT_COUNT; i++ )
        {
            min.x = MIN( min.x, recent[ i ].x );
            min.y = MIN( min.y, recent[ i ].y );
            min.z = MIN( min.z, recent[ i ].z );

            max.x = MAX( max.x, recent[ i ].x );
            max.y = MAX( max.y, recent[ i ].y );
            max.z = MAX( max.z, recent[ i ].z );
        }

        vec_d3 V = (vec_d3) 
        {
            .x = max.x - min.x,
            .y = max.y - min.y,
            .z = max.z - min.z
        };

        variation = sqrt(
                         V.x * V.x  +
                         V.y * V.y  +
                         V.z * V.z
                         );
    }

    // smooth it
    static double var_smoothed = DOUBLE_EMPTY;
    {
        if ( var_smoothed == DOUBLE_EMPTY )
        {
            var_smoothed = variation;
            return;
        }
        SMOOTH_IP( var_smoothed, variation, 0.9 );
    }


    // see if it's just passed a peak
    {
        static double varSmoothed_last = DOUBLE_EMPTY;
        if ( varSmoothed_last == DOUBLE_EMPTY )
        {
            varSmoothed_last = var_smoothed;
            return;
        }

        static double varSmoothed_preLast = DOUBLE_EMPTY;
        if ( varSmoothed_preLast == DOUBLE_EMPTY )
        {
            varSmoothed_preLast = varSmoothed_last;
            varSmoothed_last = var_smoothed;
            return;
        }

#define THRESHOLD_IMPULSE .15

        if ( varSmoothed_last > varSmoothed_preLast  
            &&  varSmoothed_last > var_smoothed  
            &&  varSmoothed_last > THRESHOLD_IMPULSE )
        {
            LOG ( @"PotPeak @ %f", varSmoothed_last );

            // hit a peak at imp_last
            [self peakedWithImpulse: varSmoothed_last ];
        }

        varSmoothed_preLast = varSmoothed_last;
        varSmoothed_last = var_smoothed;
    }
}