Device Movement using Accelerometer Reading

Question

Hi,
I am trying to find a small movement of my Windows Phone device using Accelerometer reading.
 I got this
article which uses GPS location as the initial point and then find the direction using accelerometer reading.
I tried to implement the same, but not able to get the data. Its always "NaN". Also I followed this
article for accelerometer reading.
Please see if you can help me in this case.
Thanks
Somnath

Answer 1

Thanks for your reply.
Here is the code that I am using to get the distanced moved by the device. But even if the devices is stable I see accelerometer reading. I am following
this article and trying to get the speed,accelerometer,distances covered by the device, so that when I hold the device in my hand and talk a distance of 1m I should get a distance and the new coordinates also.
  static Double earthRadius = 6378D;
        String prevLatitude = "50.9847845229511";
        String prevLongitude = "37.7661668451207";
        String currentDirection = "45";
        Double initialVelocity = 0.0;
        Double prevDistanceTravelled = 0.0;
        float PrevAcceleration = 0;
        Double PrevSpeed = 0.0;
        private double _ax = 0.0;
        private double _ay = 0.0;
        private double _az = 0.0;
        private const int _num = 100;
        private double[] _x = new double[_num];
        private double[] _y = new double[_num];
        private double[] _z = new double[_num];
        private int _index = 0;
        double distanceX, distanceY, distanceZ;
        double speedX, speedY, speedZ;       private async Task<int> CalculateAccelerometerReading(AccelerometerReading reading)
            //Average of 100 Accelerometer readings
            _x[_index] = reading.AccelerationX;
            _y[_index] = reading.AccelerationY;
            _z[_index] = reading.AccelerationZ;
            _index++;
            if (_index >= _num)
                _index = 0;
            double xsum = 0.0;
            double ysum = 0.0;
            double zsum = 0.0;
            for (int i = 0; i < _num; i++)
                xsum += _x[i];
                ysum += _y[i];
                zsum += _z[i];
            double x = xsum / _num;
            double y = ysum / _num;
            double z = zsum / _num;
            if (x > 0.5)
                x = 0.5;
            else if (x < -0.5)
                x = -0.5;
            if (y > 0.5)
                y = 0.5;
            else if (y < -0.5)
                y = -0.5;
            if (z > 0.5)
                z = 0.5;
            else if (z < -0.5)
                z = -0.5;
            //Get Current Time to calculate time Travelling - In seconds
            // var secondsTravelling = 5;// date - tripStartTime;
            //  var t = 5;// secondsTravelling.TotalSeconds;
            double t = (reading.Timestamp.Ticks - _time) / 10000000.0;
            // Compute average accelerations during this time interval
            double ax = ((x * _gravity) + _ax) / 2.0;
            double ay = ((y * _gravity) + _ay) / 2.0;
            double az = ((z * _gravity) + _az) / 2.0;
            //calculare velocity
            double vx = _vx + (ax * t);
            double vy = _vy + (ay * t);
            //calculate distances
            distanceX = (initialVelocity * t) + (0.5 * ax * t * t);
            distanceY = (initialVelocity * t) + (0.5 * ay * t * t);
            distanceZ = (initialVelocity * t) + (0.5 * az * t * t);
            //calculate speed
            speedX = distanceX / t;
            speedY = distanceY / t;
            speedZ = distanceZ / t;
            //float currentAcceleration = (float)Math.Sqrt(reading.AccelerationX * reading.AccelerationX + reading.AccelerationY * reading.AccelerationY + reading.AccelerationZ * reading.AccelerationZ);
            float currentAcceleration = (float)Math.Sqrt(ax * ax + ay * ay + az * az) - PrevAcceleration;
          //  var distanceTravelled = (initialVelocity * t) + (0.5 * currentAcceleration * t * t);
            var distanceTravelled = (float)Math.Sqrt(distanceX * distanceX + distanceY * distanceY + distanceZ * distanceZ);
          //  distanceTravelled = distanceTravelled / 1000;
            var finalvelocity = initialVelocity + (currentAcceleration * t);
            //var currentSpeed = distanceTravelled / t;
            var currentSpeed = (float)Math.Sqrt(speedX * speedX + speedY * speedY + speedZ * speedZ);
            var oldLatitude = Double.Parse(prevLatitude);
            var oldLongitude = Double.Parse(prevLongitude);
            var direction = Double.Parse(currentDirection);
            if (distanceTravelled != prevDistanceTravelled && currentAcceleration > 0.5 && currentSpeed != PrevSpeed)
                prevDistanceTravelled = distanceTravelled;
                PrevSpeed = currentSpeed;
                PrevAcceleration = currentAcceleration;
                //Convert from Degree to Radians (For Formula)
                oldLatitude = Math.PI * oldLatitude / 180;
                oldLongitude = Math.PI * oldLongitude / 180;
                direction = Math.PI * direction / 180.0;
                //Calculate the New Longitude and Latitude
                var newLatitude = Math.Asin(Math.Sin(oldLatitude) * Math.Cos(distanceTravelled / earthRadius) + Math.Cos(oldLatitude) * Math.Sin(distanceTravelled / earthRadius) * Math.Cos(direction));
                var newLongitude = oldLongitude + Math.Atan2(Math.Sin(direction) * Math.Sin(distanceTravelled / earthRadius) * Math.Cos(oldLatitude), Math.Cos(distanceTravelled / earthRadius) - Math.Sin(oldLatitude) * Math.Sin(newLatitude));
                //Convert From Radian to degree/Decimal
                newLatitude = 180 * newLatitude / Math.PI;
                newLongitude = 180 * newLongitude / Math.PI;
                prevLatitude = newLatitude.ToString();
                prevLongitude = newLongitude.ToString();
                initialVelocity = finalvelocity;
                _time = reading.Timestamp.Ticks;
                _ax = ax;
                _ay = ay;
                _az = az;
                _vx = vx;
                _vy = vy;
                Deployment.Current.Dispatcher.BeginInvoke(() =>
                    txtlatnew.Text = newLatitude.ToString();
                    txtlngnew.Text = newLongitude.ToString();
            return 0;
It would be really nice if you could help me to fix this code.