CODEWITHSUNDEEP
iosiphoneswiftscenekitarkit
unknown_jy
unknown_jy

Reputation: 767

ARKit - keep getting [0,0,0] for camera position

I am trying to get the position of the camera in the 3D space in the global coordinates.

override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        sceneView.delegate = self
        sceneView.showsStatistics = true
        sceneView.session.delegate = self
    }

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    // Create a session configuration with plane detection
    let configuration = ARWorldTrackingConfiguration()
    configuration.worldAlignment = .gravityAndHeading
    // Run the view's session
    sceneView.session.run(configuration)
}

func session(_ session: ARSession, didUpdate frame: ARFrame) {
        print(frame.camera.transform)
    }

I run the above code and below is an example output I get

Optional(simd_float4x4([[-0.739868, -0.052769, -0.670678, 0.0)], [-0.569322, 0.580241, 0.582402, 0.0)], [0.358422, 0.812733, -0.459345, 0.0)], [0.0, 0.0, 0.0, 1.0)]])) Optional(simd_float4x4([[-0.790284, -0.0315036, -0.611929, 0.0)], [-0.510883, 0.585261, 0.629656, 0.0)], [0.338302, 0.810233, -0.478617, 0.0)], [0.0, 0.0, 0.0, 1.0)]])) Optional(simd_float4x4([[-0.828626, -0.0174089, -0.559531, 0.0)], [-0.458209, 0.595292, 0.660054, 0.0)], [0.321594, 0.803321, -0.501252, 0.0)], [0.0, 0.0, 0.0, 1.0)]])) Optional(simd_float4x4([[-0.862658, -0.00656158, -0.505744, 0.0)], [-0.404869, 0.608273, 0.682703, 0.0)], [0.303151, 0.793701, -0.527388, 0.0)], [0.0, 0.0, 0.0, 1.0)]])) Optional(simd_float4x4([[-0.898201, 0.0059859, -0.43954, 0.0)], [-0.337589, 0.631021, 0.698458, 0.0)], [0.28154, 0.775742, -0.564764, 0.0)], [0.0, 0.0, 0.0, 1.0)]])) Optional(simd_float4x4([[-0.920434, 0.0197568, -0.390395, 0.0)], [-0.284616, 0.650707, 0.703969, 0.0)], [0.267941, 0.759072, -0.593311, 0.0)], [0.0, 0.0, 0.0, 1.0)]])) Optional(simd_float4x4([[-0.940432, 0.041811, -0.337396, 0.0)], [-0.224465, 0.668996, 0.708559, 0.0)], [0.255342, 0.742089, -0.619762, 0.0)], [0.0, 0.0, 0.0, 1.0)]])) Optional(simd_float4x4([[-0.960581, 0.0803864, -0.266119, 0.0)], [-0.141218, 0.683463, 0.716193, 0.0)], [0.239455, 0.725546, -0.64517, 0.0)], [0.0, 0.0, 0.0, 1.0)]])) Optional(simd_float4x4([[-0.969532, 0.108638, -0.219551, 0.0)], [-0.0873999, 0.683869, 0.724349, 0.0)], [0.228836, 0.721471, -0.653539, 0.0)], [0.0, 0.0, 0.0, 1.0)]]))

As you can see, The 4th column is always [0.0, 0.0, 0.0, 1.0] even when I am moving my phone around. Can someone help me with understanding this 4x4 matrix (I think it is the camera rotation concatenated with the position in global coordinate i.e. camera extrinsic parameters).

Upvotes: 2

Views: 784

Answers (2)

jiawen
jiawen

Reputation: 1208

I think the [0,0,0,1] is the 4th row, which stays constant all the time. It is just a padding row to make matrix multiplication work nicely.

Upvotes: 0

Noah Witherspoon
Noah Witherspoon

Reputation: 57149

It can take a while (in my experience, 10–15 seconds on an iPhone 7) for ARKit to get enough camera / motion data to provide positional tracking; until then, it can only give you orientation, and the position will be—as you’re observing—(0,0,0). To handle this, you can implement the session:cameraDidChangeTrackingState: method and check the camera’s trackingState—when it switches from notAvailable or limited to normal, then you can start using the position data.

Upvotes: 3

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