You are previewing Learning iPhone Programming.

Learning iPhone Programming

Cover of Learning iPhone Programming by Alasdair Allan Published by O'Reilly Media, Inc.
  1. Learning iPhone Programming
    1. SPECIAL OFFER: Upgrade this ebook with O’Reilly
    2. A Note Regarding Supplemental Files
    3. Preface
      1. Who Should Read This Book?
      2. What Should You Already Know?
      3. What Will You Learn?
      4. What’s in This Book?
      5. Conventions Used in This Book
      6. Using Code Examples
      7. How to Contact Us
      8. Safari® Books Online
      9. Acknowledgments
    4. 1. Why Go Native?
      1. The Pros and Cons
      2. The Release Cycle
      3. Build It and They Will Come
    5. 2. Becoming a Developer
      1. Registering As an iPhone Developer
      2. Enrolling in the iPhone Developer Program
      3. The Apple Developer Connection
      4. Installing the iPhone SDK
      5. Preparing Your iPhone or iPod touch
    6. 3. Your First iPhone App
      1. Objective-C Basics
      2. Creating a Project
    7. 4. Coding in Objective-C
      1. Declaring and Defining Classes
      2. Memory Management
      3. Fundamental iPhone Design Patterns
      4. Conclusion
    8. 5. Table-View-Based Applications
      1. Simplifying the Template Classes
      2. Creating a Table View
      3. Building a Model
      4. Connecting the Controller to the Model
      5. Adding Navigation Controls to the Application
      6. Adding a City View
      7. Edit Mode
    9. 6. Other View Controllers
      1. Utility Applications
      2. Tab Bar Applications
      3. Modal View Controllers
      4. The Image Picker View Controller
    10. 7. Connecting to the Network
      1. Detecting Network Status
      2. Embedding a Web Browser in Your App
      3. Sending Email
      4. Getting Data from the Internet
    11. 8. Handling Data
      1. Data Entry
      2. Parsing XML
      3. Parsing JSON
      4. Regular Expressions
      5. Storing Data
    12. 9. Distributing Your Application
      1. Adding Missing Features
      2. Building and Signing
      3. Submitting to the App Store
      4. Reasons for Rejection
    13. 10. Using Sensors
      1. Hardware Support
      2. Using the Camera
      3. The Core Location Framework
      4. Using the Accelerometer
      5. Using the Digital Compass
      6. Accessing the Proximity Sensor
      7. Using Vibration
    14. 11. Geolocation and Mapping
      1. User Location
      2. Annotating Maps
    15. 12. Integrating Your Application
      1. Application Preferences
      2. Custom URL Schemes
      3. Media Playback
      4. Using the Address Book
    16. 13. Other Native Platforms
      1. PhoneGap
      2. MonoTouch
    17. 14. Going Further
      1. Cocoa and Objective-C
      2. Web Applications
      3. Core Data
      4. Push Notifications
      5. In-App Purchase
      6. Core Animation
      7. Game Kit
      8. Writing Games
      9. Look and Feel
      10. Hardware Accessories
    18. Index
    19. About the Author
    20. Colophon
    21. SPECIAL OFFER: Upgrade this ebook with O’Reilly

Using the Accelerometer

The iPhone’s accelerometer measures the linear acceleration of the device so that it can report its roll and pitch, but not its yaw.


Yaw, pitch, and roll refer to the rotation of the device in three axes. If you think about an aircraft in the sky, pushing the nose down or pulling it up modifies the pitch angle of the aircraft. However, if you keep the nose straight ahead, you can also modify the roll of the aircraft using the flaps; one wing will come up, the other will go down. Finally, keeping the wings level you can use the tail flap to change the heading (or yaw) of the aircraft (rotating it in a 2D plane).

If you are dealing with an iPhone 3GS, which has a digital compass, you can combine the accelerometer and magnetometer readings to have roll, pitch, and yaw measurements (see the following section for details on how to access the magnetometer).

The accelerometer reports three figures: X, Y, and Z (see Figure 10-5). Acceleration values for each axis are reported directly by the hardware as G-force values. Therefore, a value of 1.0 represents a load of approximately 1-gravity (Earth’s gravity). X corresponds to roll, Y to pitch, and Z to whether the device is front side up or front side down, with a value of 0.0 being reported when the iPhone is edge-on.

The iPhone accelerometer axes

Figure 10-5. The iPhone accelerometer axes

When dealing with acceleration measurements, you must keep ...

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