ios - 从 GLKQuaternion 中提取的意外滚动和俯仰

Question

我使用 CMAttitude 中的四元数来旋转 SceneKit 相机。我还需要使用从四元数中提取的 Y 旋转角度。我预计它会滚动，但提取后 Y 旋转角度对应于具有 -90:90 范围的间距。如何将此范围转换为 0:180 或 0:360？

- (SCNQuaternion)SCNQuaternionFromCMQuaternion:(CMQuaternion)q {

    GLKQuaternion Q = GLKQuaternionMake(q.x, q.y, q.z, q.w);
    GLKQuaternion xRotQ = GLKQuaternionMakeWithAngleAndAxis(-M_PI_2, 1, 0, 0);
    Q = GLKQuaternionMultiply(xRotQ, Q);

    double roll = atan2(2.0 * (Q.y * Q.z - Q.w * Q.x), 1.0 - 2.0 * (Q.x * Q.x + Q.y * Q.y)); // 0:180 but around X

    double pitch = RADIANS_TO_DEGREES(asin(-2.0f * (Q.x * Q.z + Q.w * Q.y))); // 0:90 around Y

    NSLog(@"%f", pitch);
    // ...

    CMQuaternion rq = {.x = Q.x, .y = Q.y, .z = Q.z, .w = Q.w};

    return SCNVector4Make(rq.x, rq.y, rq.z, rq.w);
}

Answer 1

我是这样找到的:

- (SCNQuaternion)SCNQuaternionFromCMQuaternion:(CMQuaternion)q {

    GLKQuaternion Q = GLKQuaternionMake(q.x, q.y, q.z, q.w);
    GLKQuaternion xRotQ = GLKQuaternionMakeWithAngleAndAxis(-M_PI_2, 1, 0, 0);
    Q = GLKQuaternionMultiply(xRotQ, Q);

    double gx = 2.0 * (Q.y * Q.w - Q.x * Q.z);
    //double gy = 2.0 * (Q.x * Q.y + Q.z * Q.w);
    double gz = Q.x * Q.x - Q.y * Q.y - Q.z * Q.z + Q.w * Q.w;

    double pitch = RADIANS_TO_DEGREES(-asin( -2.0 * (Q.y * Q.w - Q.x * Q.z))); 

    if (gx >= 0 && gz < 0)
        pitch = 180 - pitch;
    else if (gx < 0 && gz < 0)
        pitch = 180 - pitch;
    else if (gx < 0 && gz >= 0)
        pitch = 360 + pitch;

    NSLog(@"%f", pitch); // now it has 0-360 range

    CMQuaternion rq = {.x = Q.x, .y = Q.y, .z = Q.z, .w = Q.w};

    return SCNVector4Make(rq.x, rq.y, rq.z, rq.w);
}