iphone - 如何创建新的CMAttitude引用系以使重力位于Y轴上

Question

我希望能够更改设备运动管理器引用系(对于陀螺仪)，以便我的重力矢量位于 Y 轴上。

通常，当您启动设备运动管理器更新时，您只会使手机的 z 轴与重力对齐。

您可以更改此设置以使用磁力计使 x 轴与磁北极或真北极对齐。这样我的 X 轴就指向北，Z 轴就指向下。

我想要做的是让我的 Y 轴(负)指向下(以便它与重力对齐)，并且让我的 X 轴指向真正的磁极。

我想要的结果是，当我的手机以垂直(纵向)方向静止时，手机的右侧将与北极对齐，并且我的所有读数(滚动、俯仰、偏航)将读取为 0 。然后，如果我在 X 轴上旋转手机，俯仰角就会改变，如果我绕 Y 轴旋转，偏航就会改变。

到目前为止，我知道如果我乘以先前存储的态度的倒数，我可以设置自己的引用系(就像我可以手动将手机设置在这个方向，保存该态度并简单地继续乘以新态度)通过与此存储的相反，我的所有读数将与我想要的完全一样)。

但是手动设置它不是一个选项，那么我如何以编程方式进行此设置？

我不认为有一个函数可以创建我自己的姿态引用系，或者如果至少有一个函数可以将姿态乘以旋转矩阵，那么我可能可以解决这个问题。 (因为我只是将所有姿态乘以 90 度的音高变化)。

我希望我能清楚地解释自己，

我将不胜感激任何建议。谢谢

PD:这些是 iPhone 方向坐标:

Answer 1

伪代码:

1. 开始设备 Action 更新
2. 在后台启动相机预览；)
3. 从设备捕获当前重力读数作为 CMAcceleration...一旦获得重力，请将其存储在局部变量中。
4. 然后您必须获取 2 个向量并获取它们之间的角度，在本例中为 (0,0,-1) 的设备重力和真实重力向量...
5. 然后我们将 theta 转换为 thetaPrime...与 CoreMotion 引用方向匹配的变换
6. 设置一个计时器来制作动画......
7. 在动画过程中获取motionManager的deviceMotion属性的rotationMatrix的倒数。
8. 以正确的顺序应用变换以反射(reflect)设备当前的姿态(欧拉模式下的偏航、俯仰、滚动或设备四元数旋转......基本上有 3 种不同的方式来表达同一件事)

这是代码:

- (void) initMotionCapture
{
    firstGravityReading = NO;
    referenceAttitude = nil;

    if (motionManager == nil)
    {
        self.motionManager = [CMMotionManager new];
    }
    motionManager.deviceMotionUpdateInterval = 0.01;
    self.gravityTimer = [NSTimer scheduledTimerWithTimeInterval:1/60.0 
                                 target:self 
                                 selector:@selector(getFirstGravityReading) 
                                 userInfo:nil repeats:YES];
}


- (void) getFirstGravityReading
{
    CMAcceleration currentGravity; 

    CMDeviceMotion *dm = motionManager.deviceMotion;
    referenceAttitude = dm.attitude;
    currentGravity = dm.gravity;

    [motionManager startDeviceMotionUpdates];

    if (currentGravity.x !=0 && 
        currentGravity.y !=0 && currentGravity.z !=0)
    {
        NSLog(@"Gravity = (%f,%f,%f)", 
              currentGravity.x, currentGravity.y, currentGravity.z);

        firstGravityReading = YES;
        [gravityTimer invalidate];
        self.gravityTimer = nil;
        [self setupCompass];
    }
}

- (void) setupCompass
{
    //Draw your cube... I am using a quartz 3D perspective hack!
    CATransform3D initialTransform = perspectiveTransformedLayer.sublayerTransform;
    initialTransform.m34 = 1.0/-10000;


    //HERE IS WHAT YOU GUYS NEED... the vector equations!
    NSLog(@"Gravity = (%f,%f,%f)", 
          currentGravity.x, currentGravity.y, currentGravity.z);

    //we have current gravity vector and our device gravity vector of (0, 0, -1)
    // get the dot product
    float dotProduct = currentGravity.x*0 + 
                       currentGravity.y*0 + 
                       currentGravity.z*-1;
    float innerMagnitudeProduct = currentGravity.x*currentGravity.x + 
                                  currentGravity.y + currentGravity.y + 
                                  currentGravity.z*currentGravity.z;
    float magnitudeCurrentGravity = sqrt(innerMagnitudeProduct);
    float magnitudeDeviceVector = 1; //since (0,0,-1) computes to: 0*0 + 0*0 + -1*-1 = 1

    thetaOffset = acos(dotProduct/(magnitudeCurrentGravity*magnitudeDeviceVector));
    NSLog(@"theta(degrees) = %f", thetaOffset*180.0/M_PI);

    //Now we have the device angle to the gravity vector (0,0,-1)
    //We must transform these coordinates to match our 
    //device's attitude by transforming to theta prime
    float theta_deg = thetaOffset*180.0/M_PI;
    float thetaPrime_deg = -theta_deg + 90; // ThetaPrime = -Theta + 90 <==> y=mx+b

    NSLog(@"thetaPrime(degrees) = %f", thetaOffset*180.0/M_PI);

    deviceOffsetRotation = 
        CATransform3DMakeRotation((thetaPrime_deg) * M_PI / 180.0, 1, 0, 0);
    initialTransform = CATransform3DConcat(deviceOffsetRotation, initialTransform);

    perspectiveTransformedLayer.sublayerTransform = initialTransform;

    self.animationTimer = [NSTimer scheduledTimerWithTimeInterval:1/60.0 
                                   target:self 
                                   selector:@selector(tick) 
                                   userInfo:nil 
                                   repeats:YES];

}

- (void) tick
{
    CMRotationMatrix rotation;

    CMDeviceMotion *deviceMotion = motionManager.deviceMotion;
    CMAttitude *attitude = deviceMotion.attitude;

    if (referenceAttitude != nil)
    {
        [attitude multiplyByInverseOfAttitude:referenceAttitude];
    }
    rotation = attitude.rotationMatrix;

    CATransform3D rotationalTransform = perspectiveTransformedLayer.sublayerTransform;

    //inverse (or called the transpose) of the attitude.rotationalMatrix
    rotationalTransform.m11 = rotation.m11;
    rotationalTransform.m12 = rotation.m21;
    rotationalTransform.m13 = rotation.m31;

    rotationalTransform.m21 = rotation.m12;
    rotationalTransform.m22 = rotation.m22;
    rotationalTransform.m23 = rotation.m32;

    rotationalTransform.m31 = rotation.m13;
    rotationalTransform.m32 = rotation.m23;
    rotationalTransform.m33 = rotation.m33;

    rotationalTransform = 
        CATransform3DConcat(deviceOffsetRotation, rotationalTransform);
    rotationalTransform = 
        CATransform3DConcat(rotationalTransform, 
                            CATransform3DMakeScale(1.0, -1.0, 1.0));


    perspectiveTransformedLayer.sublayerTransform = rotationalTransform;
}