使用线性加速度android计算距离 [英] Calculating distance using Linear acceleration android
问题描述
可能的重复:
Android 加速度计精度(惯性导航)
我正在使用以下代码来计算距离.tnew 和 anew 分别是包含时间戳和加速度的arraylists.
I am using the following code to calculate the distance. tnew and anew are arraylists containing timestamps and accelerations respectively.
double distance=0;
double init_vel=0;
long time_prev=tnew.next();
while(anew.hasNext())
{
float temp_acc=anew.next();
long temp_time=tnew.next();
interval=(temp_time-time_prev)/1000f; //milliseconds to seconds
double fin_vel=init_vel+(temp_acc*interval);
distance+=(init_vel*interval)+0.5f*temp_acc*interval*interval;
init_vel=fin_vel;
time_prev=temp_time;
}
代码中是否有任何逻辑错误?因为我得到的值比实际长度小得多.LogCat 的输出:
--------- beginning of /dev/log/system
--------- beginning of /dev/log/main
V/PhonetapeActivity( 8842): Sensor Listener Registered
V/PhonetapeActivity( 8842): Sensor Unregistered
V/PhonetapeActivity( 8842): No. of Iterations : 49
V/PhonetapeActivity( 8842): Value of acceleration : 3.5762787E-7
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665585965
V/PhonetapeActivity( 8842): Value of acceleration : -0.15275347
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586017
V/PhonetapeActivity( 8842): Value of acceleration : 0.15585232
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586077
V/PhonetapeActivity( 8842): Value of acceleration : 1.075269
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586138
V/PhonetapeActivity( 8842): Value of acceleration : 3.6529458
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586199
V/PhonetapeActivity( 8842): Value of acceleration : 9.645137
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586257
V/PhonetapeActivity( 8842): Value of acceleration : 17.022213
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586316
V/PhonetapeActivity( 8842): Value of acceleration : 9.721476
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586376
V/PhonetapeActivity( 8842): Value of acceleration : -18.729362
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586437
V/PhonetapeActivity( 8842): Value of acceleration : -22.868385
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586497
V/PhonetapeActivity( 8842): Value of acceleration : -16.777517
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586557
V/PhonetapeActivity( 8842): Value of acceleration : -7.0492268
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586617
V/PhonetapeActivity( 8842): Value of acceleration : -3.860828
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586677
V/PhonetapeActivity( 8842): Value of acceleration : 1.7244682
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586737
V/PhonetapeActivity( 8842): Value of acceleration : 5.0734243
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586797
V/PhonetapeActivity( 8842): Value of acceleration : 6.4193974
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586857
V/PhonetapeActivity( 8842): Value of acceleration : 2.739545
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586917
V/PhonetapeActivity( 8842): Value of acceleration : 5.559997
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665586977
V/PhonetapeActivity( 8842): Value of acceleration : 4.2290807
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587037
V/PhonetapeActivity( 8842): Value of acceleration : 5.0012918
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587097
V/PhonetapeActivity( 8842): Value of acceleration : 5.9317436
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587157
V/PhonetapeActivity( 8842): Value of acceleration : 5.20226
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587217
V/PhonetapeActivity( 8842): Value of acceleration : 7.1381693
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587276
V/PhonetapeActivity( 8842): Value of acceleration : 7.6460614
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587337
V/PhonetapeActivity( 8842): Value of acceleration : 5.566694
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587396
V/PhonetapeActivity( 8842): Value of acceleration : 3.355657
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587457
V/PhonetapeActivity( 8842): Value of acceleration : 1.8876343
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587517
V/PhonetapeActivity( 8842): Value of acceleration : -0.8815446
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587577
V/PhonetapeActivity( 8842): Value of acceleration : -0.9595623
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587646
V/PhonetapeActivity( 8842): Value of acceleration : -4.233544
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587697
V/PhonetapeActivity( 8842): Value of acceleration : -1.9580669
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587765
V/PhonetapeActivity( 8842): Value of acceleration : -1.4569702
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587822
V/PhonetapeActivity( 8842): Value of acceleration : -0.6058636
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587876
V/PhonetapeActivity( 8842): Value of acceleration : -0.21207428
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587937
V/PhonetapeActivity( 8842): Value of acceleration : 0.5068469
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665587997
V/PhonetapeActivity( 8842): Value of acceleration : 5.614555
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665588057
V/PhonetapeActivity( 8842): Value of acceleration : -4.5297813
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665588122
V/PhonetapeActivity( 8842): Value of acceleration : -0.29250193
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665588178
V/PhonetapeActivity( 8842): Value of acceleration : -2.4922757
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665588237
V/PhonetapeActivity( 8842): Value of acceleration : -1.7652755
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665588297
V/PhonetapeActivity( 8842): Value of acceleration : -2.3279366
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665588357
V/PhonetapeActivity( 8842): Value of acceleration : -1.8127642
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665588419
V/PhonetapeActivity( 8842): Value of acceleration : -1.956768
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665588477
V/PhonetapeActivity( 8842): Value of acceleration : -0.8337221
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665588537
V/PhonetapeActivity( 8842): Value of acceleration : -0.24841261
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665588601
V/PhonetapeActivity( 8842): Value of acceleration : 0.23997736
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665588657
V/PhonetapeActivity( 8842): Value of acceleration : 0.14441395
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665588723
V/PhonetapeActivity( 8842): Value of acceleration : 0.23150349
V/PhonetapeActivity( 8842): Value of timestamp(milli) : 1350665588777
V/PhonetapeActivity( 8842): 1st while loop ended
V/PhonetapeActivity( 8842): 2nd while loop ended
V/PhonetapeActivity( 8842): Avg value : 0.4006781578063965
V/PhonetapeActivity( 8842): Max Value : 17.022213
V/PhonetapeActivity( 8842): Min Value : -22.868385
V/PhonetapeActivity( 8842): Standard Deviation : -0.0031174493
V/PhonetapeActivity( 8842): 3rd while loop started
V/PhonetapeActivity( 8842): startpos=3 endpos=8
V/PhonetapeActivity( 8842): acceleration=0.1558523178100586 interval=0.061000000685453415
V/PhonetapeActivity( 8842): distance=5.799264876044276E-4
V/PhonetapeActivity( 8842): next init velocity=0.009506991493243078
V/PhonetapeActivity( 8842): acceleration=1.0752689838409424 interval=0.061000000685453415
V/PhonetapeActivity( 8842): distance=0.005160928954000712
V/PhonetapeActivity( 8842): next init velocity=0.07509840024458736
V/PhonetapeActivity( 8842): acceleration=3.6529457569122314 interval=0.057999998331069946
V/PhonetapeActivity( 8842): distance=0.021805144861910285
V/PhonetapeActivity( 8842): next init velocity=0.2869692480489858
V/PhonetapeActivity( 8842): acceleration=9.645136833190918 interval=0.05900000035762787
V/PhonetapeActivity( 8842): distance=0.07231105232279186
V/PhonetapeActivity( 8842): next init velocity=0.8560323246566197
V/PhonetapeActivity( 8842): acceleration=17.022212982177734 interval=0.05999999865889549
V/PhonetapeActivity( 8842): distance=0.18495295465057213
V/PhonetapeActivity( 8842): next init velocity=1.8773650807587172
V/PhonetapeActivity( 8842): 3rd while loop ended
V/PhonetapeActivity( 8842): final distance=0.18495295465057213
V/PhonetapeActivity( 8842): values of acceleration, timestamp, distance, start_time and calibrating reset
如果您观察 logcat，首先它会迭代 49 个加速度值及其各自的时间戳(以毫秒为单位).然后是平均值、总和、最大值、最小值等.
然后，如果您看到有 startpos=3 和 endpos=8.这是迭代次数范围，我用来计算距离.即，我仅使用迭代 3 到 8 的加速度和时间戳值.
这是因为，我从 加速度上升到相反方向的突然变化.您可以看到 3-8 中的值符合逻辑.从 3 开始，加速度有相当大的上升，而在 8 之后突然下降.
If you observe the logcat, first it iterates through 49 values of acceleration and their respective time stamps in milliseconds. Then there is a avg, sum, max, min etc.
Then if you see there is a startpos=3 and endpos=8. This is the iteration number range, I am using to calculate the distance .i.e I am using the values of acceleration and timestamp only from iteration 3 to 8.
This is because, I detect the start of distance calculation from a rise in acceleration to a sudden change in the opposite direction. You can see that the values from 3-8 fit into the logic. From 3 there is a considerable rise in acceleration and after 8 there is a sudden decrease.
推荐答案
加速度计非常精确，但不擅长航位推算.陀螺仪擅长于此，但它们会随着时间的推移而漂移".Sensor-fusion"是使用加速度/陀螺仪数据串联的过程用另一个来纠正一个人的不足.AFAIR，传感器融合"未在 Galaxy Ace 上启用.LINEAR_ACCELERATION 只不过是 ACCELEROMETER - 重力组件.在没有陀螺仪的设备上，根据定义，融合是不可能的，它需要加速 + 陀螺仪.
Accelerometers are very precise but bad at dead-reckoning. Gyroscopes are good at that but they "drift" over time. "Sensor-fusion" is the process of using accel/gyro data in tandem to correct one's deficiency using the other. AFAIR, "sensor-fusion" is NOT enabled on Galaxy Ace. LINEAR_ACCELERATION is nothing but ACCELEROMETER - gravity component. On devices without gyroscope, fusion is not possible by definition it requires accel+gyro.
加速度计数据包含 9.8 的重力分量.这是通过简单地确定加速度计数据的 2 个连续样本之间的差异来过滤掉的.这为我们提供了 LINEAR_ACCELERATION 数据.
The accelerometer data contains the gravity component of 9.8. This is filtered out by simply determining the difference between 2 consecutive samples of accelerometer data. This gives us the LINEAR_ACCELERATION data.
查看实际内部代码:
frameworks/base/services/sensorservice/LinearAccelerationSensorc一>
函数 LinearAccelerationSensor::process() 在上述文件中很重要.
Check this out for actual internal code :
frameworks/base/services/sensorservice/LinearAccelerationSensor.cpp
The function LinearAccelerationSensor::process() is of interest in the above file.
还有一些基本的操作，比如上面链接和视频所说的过滤/平均，需要在你的应用程序中获得的加速数据上执行.以这种方式获得的处理值将比原始值更好(尽管不如在您的设备上存在传感器融合的情况下获得的值好).然后可以使用这些来更准确地计算速度和位置.
Also rudimentary operations like filtering/averaging that the above link and video talk about, need to performed on the accel data obtained in your app. The processed values obtained in this manner will be better(though not as good as the ones that would have been obtaioned had sensor fusion been present on your device) than the raw values. These can then be used to calculate the velocity and position more accurately.
也就是说，每秒 16 个样本(@poll-rate=60ms)本身就相对不准确.您可能想尝试使用 SENSOR_DELAY_FASTEST 注册 sensorEventListner 以查看您可以在设备上获得的最大样本数.
That said, 16 samples a second (@poll-rate=60ms) is relatively inaccurate in itself. You might want to try registering the sensorEventListner using SENSOR_DELAY_FASTEST to see the maximum number of samples that you can obtain on you device.
另请注意，手机上的加速度计被限制在特定的 MAX 灵敏度(通常为 -/+ 2/4/8 G 范围).虽然正常的步行/跑步可能会在这些范围内运行，但突然的加速脉冲(例如在自行车上)肯定会被限制在 MAX 上，并且您将在航位推算中失去同步.这可以通过记录非常接近 -/+MAX 的样本数来检查.-/+MAX 处的大量样本意味着您肯定会失去与实际位置的同步.
Also note that the accelerometers on phones are clamped to certain MAX sensitivity (usually -/+ 2/4/8 G range). While normal walking/running might operate under these ranges, a sudden impulse in acceleration (for example on a bike) will definitely be clamped to the MAX and you will lose sync in dead-reckoning. This can be checked by noting the number of samples that are very close to the -/+MAX. Lot of samples at -/+MAX imply that you would have most certainly lost sync with the actual position.
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