Monday, 11 April 2011

WP7 Tutorial - part 5: Orientation and Acceleration - X,Y,Z

Detecting gestures, orientations, and movement can be realized with the accelerometer. The accelerometer is a sensor that measures the acceleration in 3 dimensions (X, Y, and Z). If the device is not moved the accelerations measure are the gravity forces in each direction. If the device is accelerated the measured results are a combination of the acceleration and the gravity.

The accelerometer data can be accessed via the AccelerometerReadingEventArgs class. The class has values for the X, Y, and Z axis. The values are of type double and between -2 and 2 which related to acceleration "for each axis in gravitational units" - 1 is the gravitational force of the earth. See: http://msdn.microsoft.com/en-us/library/ff431744(v=vs.92).aspx and http://msdn.microsoft.com/en-us/library/ff431810(v=vs.92).aspx or on page 80ff, C. Petzold, Programming Windows Phone 7.

A typical exercise for understanding the accelerometer is to create a bubble level (a tool to measure if something is horizontal or vertical - e.g. for hanging pictures on the wall). You probably want to freshen up on arctan2 - at least I needed ;-)

See below the c# example reading out the accelerometer on a windows phone 7. You can also download the accelerometer project directory in a single ZIP-file.

using System;
using System.Windows;
using Microsoft.Phone.Controls;
using Microsoft.Devices.Sensors;

// A simple example to read the accelerometer and display the values
// In order to make it work you have to add the refercerence to 
// Microsoft.Devices.Sensors to your project. To do this right-click
// in the Solution Explorer on References and than choose add Reference
// in the dialog then select Microsoft.Devices.Sensors
// Albrecht Schmidt, University of Stuttgart

// for a more comprehensive example see: 
// http://msdn.microsoft.com/en-us/library/ff431810(v=vs.92).aspx
// http://msdn.microsoft.com/en-us/library/ff431744(v=vs.92).aspx
// and page 80ff, C. Petzold, Programming Windows Phone 7

namespace Accl_X_Y_Z
{
    public partial class MainPage : PhoneApplicationPage
    {
        Accelerometer accelerometer;
    
        public MainPage()
        {
            InitializeComponent();
            // create a new instance
            accelerometer = new Accelerometer();
            // register a callback function for when values change
            accelerometer.ReadingChanged += new EventHandler<AccelerometerReadingEventArgs>(accelerometer_ReadingChanged);
            // start the accelerometer
            accelerometer.Start();
        }

        void accelerometer_ReadingChanged(object sender, AccelerometerReadingEventArgs e)
        {
            // required as from here the textBlocks cannot be accessed
            Deployment.Current.Dispatcher.BeginInvoke(() => ChangeUI(e));
        }
        
        void ChangeUI(AccelerometerReadingEventArgs e)
        {
            // show the values on the screen
            textBlock1.Text = "X: " + e.X.ToString("0.000");
            textBlock2.Text = "Y: " + e.Y.ToString("0.000");
            textBlock3.Text = "Z: " + e.Z.ToString("0.000");
        }
    }
}

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