Get Camera Translation from ARCamera

Question

I am experimenting with Apple's ARKit and have a question regarding camera transformations. Which of the values in the transform matrix represent how far the user has travelled from the point of origin? Calling

self.sceneView.session.currentFrame!.camera.transform.columns.0.x 

does not seem to yield the correct X translation.

Additionally, what would be the correct location for Y and Z?

Answer 1

The last column of a 4x4 transform matrix -- matrix.columns.3 in this case -- is the translation vector. See this old answer for some background on 4x4 transform matrices and how they work.

Answer 2

The simplest way to get ARCamera's translation is the following:

func getCameraTransform(for sceneView: ARSCNView) -> MDLTransform {
    guard let transform = sceneView.session.currentFrame?.camera.transform else { return }
    return MDLTransform(matrix: transform)
}

let position = SCNVector3(cameraTransform.translation.x, 
                          cameraTransform.translation.y, 
                          cameraTransform.translation.z)