Question

过去一周对此进行了大量研究，但找不到类似的问题。我正在Apple Watch上收集加速度计数据，并查看DeviceMotion类输出的时间戳，这是一个问题。时间戳记并不总是按时间顺序排列。例如，如果我以100Hz的频率收集了几分钟的运动数据，我将从在同一应用中生成的CSV文件中获得以下时间戳（这些时间戳是UTC时间戳）：

1531099702.768570
1531099702.778460
1531099702.788380
1531099702.798270
1531099702.738870
1531099702.748780
1531099702.758670
1531099702.768590

如果您注意到，在第5个时间戳记上，时间比第4个时间戳记回跳了很多。

有人知道是什么原因造成的吗？谢谢！

这是我的代码：

func startUpdates() {
    motionManager = CMMotionManager()
    if motionManager.isDeviceMotionAvailable {
        self.motionManager.deviceMotionUpdateInterval = updateInterval
        self.motionManager.showsDeviceMovementDisplay = true
        self.motionManager.startDeviceMotionUpdates(using: .xArbitraryZVertical, to: .main, withHandler: { (data, error) in
            // Make sure the data is valid before accessing it.
            if let validData = data {
                // find boot time of device to normalize timestamps
                if (self.accArray.isEmpty) {
                    self.bootTime = Date(timeIntervalSinceNow:-validData.timestamp)
                }

                self.accArray.append([validData.timestamp + self.bootTime.timeIntervalSince1970,
                                      validData.attitude.pitch,
                                      validData.attitude.roll,
                                      validData.attitude.yaw,
                                      validData.userAcceleration.x,
                                      validData.userAcceleration.y,
                                      validData.userAcceleration.z,
                                      validData.rotationRate.x,
                                      validData.rotationRate.y,
                                      validData.rotationRate.z,
                                      validData.gravity.x,
                                      validData.gravity.y,
                                      validData.gravity.z])

                if (self.accArray.count == 100) {
                    let accChunk = NSKeyedArchiver.archivedData(withRootObject: self.accArray)
                    watchSessionManager.sharedManager.sendMessageData(accChunk: accChunk)
                    self.reset()
                }
            }
        })
    }
}

将accArray中的所有数据插入到CSV文件中，该文件以以下方式生成：

// Create CSV with collected array
    func createCSV() -> String {
        if(self.accArray.count == 0) {
            return("No data captured")
        }
        else {
            // Create CSV structure
            var csvText = "Number,Pitch,Roll,Yaw,RotX,RotY,RotZ,GravX,GravY,GravZ,AccX,AccY,AccZ,Time\n"
            for index in 0...accArray.count-1 {
                let newLine = [String(index),
                               String(accArray[index][1]),
                               String(accArray[index][2]),
                               String(accArray[index][3]),
                               String(accArray[index][4]),
                               String(accArray[index][5]),
                               String(accArray[index][6]),
                               String(accArray[index][7]),
                               String(accArray[index][8]),
                               String(accArray[index][9]),
                               String(accArray[index][10]),
                               String(accArray[index][11]),
                               String(accArray[index][12]),
                               String(accArray[index][0])].joined(separator: ",")
                // Insert data into CSV file
                csvText.append(newLine + "\n")
            }
            self.reset()
            return(csvText)
        }
    }

CMMotionManager中的时间戳不正确

0 个答案: