scenekit - cameranode rotate as iOS device moving

Question

It's 360 degree video player project.

I add a cameranode(SCNNode) to a rootnode, the cameranode was put at the center(0,0,0) of the SCNSphere, It can play video by now.

Now I have to use devicemotion. I need to rotate the camera when device moves. Not just rotate a certain angle. (Not just device move, When I'm holding a device, my moving regard as the device moving. because I found if I use deviceMotion.attitude.roll, the cameranode only moves when device moves by itself, not when I circle around with device)

When device is located in (x1,y1,z1) position, the cameranode would rotate as the device moving, and when the device located in (x1,y1,z1) position again, the view should be as same as the last we left.

Here's what I've done:

if (self.motionManager.gyroAvailable) {
        self.motionManager.gyroUpdateInterval = 1.0/60.0;
        [self.motionManager startGyroUpdatesToQueue:self.queue withHandler:^(CMGyroData *gyroData, NSError *error){
            if (error) {
                [self.motionManager stopGyroUpdates];
                NSLog(@"Gyroscope encountered error:%@",error);
            }else {
                CGFloat tempX = 0;
                CGFloat tempY = 0;
                CGFloat tempZ = 0;
                if ((fabs(gyroData.rotationRate.y)/60) > 0.002) {
                    tempY = gyroData.rotationRate.y/60;
                }
                tempX = gyroData.rotationRate.x/60;
                tempZ = gyroData.rotationRate.z/60;
                [self.cameraNode runAction:[SCNAction rotateByX:-tempY y:tempX z:tempZ duration:0]];
            }
        }];
    }else {
        NSLog(@"This device has no gyroscope");
    }

The math could be wrong, I don't know why would I divide 60, but it seems the nearest value I need when I use [self.cameraNode runAction:[SCNAction rotateByX:-tempY y:tempX z:tempZ duration:0]];

Here's the problem?

1. which data should I use?

CMGyroData or CMDeviceMotion. If use CMDeviceMotion, which specific value should I use? deviceMotion.attitude, deviceMotion.attitude.quaternion, deviceMotion.gravity

2. which is the right method to rotate a cameranode? There are many methods, I'm not sure.

+ (SCNAction *)rotateByX:(CGFloat)xAngle y:(CGFloat)yAngle z:(CGFloat)zAngle duration:(NSTimeInterval)duration;

+ (SCNAction *)rotateToX:(CGFloat)xAngle y:(CGFloat)yAngle z:(CGFloat)zAngle duration:(NSTimeInterval)duration;

Answer 1

Device motion is best, as it ties in multiple sensors and fuses the data together in a meaningful way. It's also best to avoid using euler angles, as they suffer from what's known as gimbal lock. Instead, use quaternions and set your camera orientation with them.

I've created a Swift class extension for CMDeviceMotion that'll let you determine what the device is looking at (for any orientation of the screen).

From there, it's straightforward to rotate your camera. First, setup your device motion (in view did appear, or some other appropriate place):

if motionManager.deviceMotionAvailable {

    motionManager.deviceMotionUpdateInterval = 0.017
    motionManager.startDeviceMotionUpdatesToQueue(NSOperationQueue(), withHandler: deviceDidMove)
}

Then handle those updates in your deviceDidMove implementation, using the previously mentioned CMDeviceMotion extension:

func deviceDidMove(motion: CMDeviceMotion?, error: NSError?) {

    if let motion = motion {

        yourCameraNode.orientation = motion.gaze(atOrientation: UIApplication.sharedApplication().statusBarOrientation)
    }
}

And now your camera should follow your devices orientation in space.