How can i get device tilt in xamarin forms? - xamarin

Question

I´d like to get the tilt of the device, so i can use this to mesure the tilt os some surface, laying down the device over the surface.
Right now i am using Device Motion Plugin for xamarin forms from here https://github.com/rdelrosario/xamarin-plugins
and the code below:
CrossDeviceMotion.Current.Start(MotionSensorType.Accelerometer);
CrossDeviceMotion.Current.SensorValueChanged += (s, a) =>
{
switch (a.SensorType)
{
case MotionSensorType.Accelerometer:
{
Debug.WriteLine("A: {0},{1},{2}", ((MotionVector)a.Value).X, ((MotionVector)a.Value).Y,
((MotionVector)a.Value).Z);
Exposicao.Inclinacao = ((MotionVector)a.Value).Z;
break;
}
case MotionSensorType.Compass:
{
// Debug.WriteLine("H: {0}", a.Value);
Exposicao.Bussola = (double)a.Value.Value;
break;
}
}
};
The compass part is ok, the accelerometer part is working but there are some but´s.
If i am not wrong, i get the tilt in Z axis, so z.Value.Value.
This value is diferent for android and ios, lets focus in android.
z values are from 10 when device is laying down on flat surface, to 0 if device is stand up, lets focus only in just one quadrant.
I am doing something wrong to achieve what i explained?
How can i convert those values to a Angle between 0 and 90? It seems not linear, so the 5 does not seem 45 degrees.
Thanks

Answer 1

I'd probably roll out my own platform implementation for the feature you're looking for. The DeviceMotion library looks a bit simple for your purposes, as can be seen from the answer below. I'm pretty sure you can use it as a good starting point but it needs to be extended a little.
Android
On Android, you should use the Rotation Vector Sensor which uses a Kalman filter (with accelerometer, magnetometer and gyroscope) to get accurate measurements of the device's rotation:
The rotation vector represents the orientation of the device as a combination of an angle and an axis, in which the device has rotated through an angle θ around an axis (x, y, or z).
Image from the official Android documentation
iOS:
For iOS, you have to do a bit more work yourself. The key is to make use of CMAttitude, which describes the attitude of the device relative to an initial attitude. I found a snippet I've saved to my collection from an unknown source (can't credit the original author) here:
public void CalculateLeanAngle ()
{
motionManager = new CMMotionManager ();
motionManager.DeviceMotionUpdateInterval = 0.02;
if (motionManager.DeviceMotionAvailable) {
motionManager.StartDeviceMotionUpdates(CMAttitudeReferenceFrame.XArbitraryZVertical, NSOperationQueue.CurrentQueue, (data, error) => {
CMQuaternion quat = motionManager.DeviceMotion.Attitude.Quaternion;
double x = quat.x;
double y = quat.y;
double w = quat.w;
double z = quat.z;
double degrees = 0.0;
//Roll
double roll = Math.Atan2 (2 * y * w - 2 * x * z, 1 - 2 * y * y - 2 * z * z);
degrees = Math.Round (-applyKalmanFiltering (roll) * 180.0 / Constants.M_PI);
});
}
public double applyKalmanFiltering (double yaw)
{
if (motionLastYaw == 0)
motionLastYaw = yaw;
float q = 0.1f; // process noise
float r = 0.1f; // sensor noise
float p = 0.1f; // estimated error
float k = 0.5f; // kalman filter gain
double x = motionLastYaw;
p = p + q;
k = p / (p + r);
x = x + k * (yaw - x);
p = (1 - k) * p;
motionLastYaw = x;
return motionLastYaw;
}
Image from the official Xamarin documentation
I'll try to look for the original source when I have more time but I'm pretty sure this will work out of the box for your purposes.