2d barcode generator c# free A movement reporter that could be applied as a program controller in Objective-C

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Listing 17.6 A movement reporter that could be applied as a program controller
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- (void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration { accelX = ((acceleration.x * kFilteringFactor) + (accelX * (1 - kFilteringFactor))); accelY = ((acceleration.y * kFilteringFactor) + (accelY * (1 - kFilteringFactor))); accelZ = ((acceleration.z * kFilteringFactor) + (accelZ * (1 - kFilteringFactor))); float moveX = acceleration.x - accelX; float moveY = acceleration.y - accelY; float moveZ = acceleration.z - accelZ;
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Gathers filtered info
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Measures movement
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Positioning: accelerometers and location
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if (!starttime) { starttime = acceleration.timestamp; }
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Marks start time
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if (acceleration.timestamp > starttime + 1 && (fabs(moveX) >= .3 || Notes movement fabs(moveY) >= .3 || continuing fabs(moveZ) >= .3)) {
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if (fabs(moveX) > fabs(moveVector)) { moveVector = moveX; moveDir = (moveVector > 0 @"Right" : @"Left"); } if (fabs(moveY) > fabs(moveVector)) { Saves moveVector = moveY; largest moveDir = (moveVector > 0 @"Up" : @"Down"); movements } if (fabs(moveZ) > fabs(moveVector)) { moveVector = moveZ; moveDir = (moveVector > 0 @"Forward" : @"Back"); } lasttime = acceleration.timestamp; Notes movement } else if (moveVector && acceleration.timestamp ending > lasttime + .1) { myReport.text = Reports [moveDir stringByAppendingFormat: movement @": %f.",moveVector]; moveDir = [NSString string]; Cleans up moveVector = 0; }
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As usual, you start by creating a low-pass filter B and then taking the inverse of it C in order to get relatively clean movement data. Because the data can be a little dirty at the start, you don t accept any acceleration data sent in the first second D. You could cut this down to a mere fraction of a second. You start looking for movement whenever one of the accelerometers goes above .3 g E. When that occurs, you save the direction of highest movement F, and keep measuring it until movement drops below .3 g. Afterward, you make sure that at least a tenth of a second has passed G, so that you know you re not in a lull during a movement. Finally, you do whatever you want to do with your movement data. Listing 17.6 reports the information in a label H, but you d doubtless do something much more intricate in a live program. Cleanup is required to get the next iteration of movement reporting going I. This sample program works well, unless the movement is very subtle. In those cases, it occasionally reports the opposite direction because of the force when the device stops its motion. If this type of subtlety is a problem for your application, more work would be required. To resolve this, you d need to make a better comparison of the start and stop forces for movements; if they re similar in magnitude, you ll usually want to use the first force measured, not necessarily the biggest one. But for the majority of cases, the
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The accelerometer and gestures
code in listing 17.6 is sufficient. You ve now got an iPhone application that can accurately report (and take action based upon) direction of movement. Together gravity and force measurement represent the most obvious things that you can do with the accelerometers, but they re by no means the only things. We suspect that using the accelerometers to measure three-dimensional gestures will be one of their best (and most frequent) uses as the iPhone platform matures.
17.3 The accelerometer and gestures
Three-dimensional gestures are one of the coolest results of having accelerometers inside your iPhone. They can allow your users to manipulate your iPhone programs without ever having to touch (or even look at) the screen. To recognize a gesture, you must do two things. First, you must accurately track the movements that make up a gesture. Second, you must make sure that in doing so you won t recognize a random movement that wasn t intended to be a gesture at all. Technically, recognizing a gesture requires only the coding foundation that we ve discussed already. But we re going to show one example that puts that foundation into real-world use by creating a method that recognizes a shake gesture. We re defining a shake as a rapid shaking back and forth of the iPhone, like you might shake dice in your hand before you throw them. As usual, Apple s Accelerometer Graph is a great tool to use to figure out what s going on. It shows a shake as primarily having these characteristics, presuming a program that s running in portrait mode:
Movement is primarily along the x-axis, with some movement along the y-axis, and even less along the z-axis. There are at least three peaks of movement, with alternating positive and negative forces. All peaks are at least +/-1 g, with at least one peak being +/-2 g for a relatively strong shake.
We can use the preceding characteristics to define the average requirements for a shake. If we wanted to tighten them up, we d probably require four or more peaks of movement, but for now, this will do. Alternatively, we might want to decrease the gforce requirements so that users don t have to shake their iPhone quite as much (and, in fact, we will). We ve detailed the code that will watch for a shake in listing 17.7.
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