Question

我对ARKit很新（准确地说是2天），我在点击时尝试在我的ARSCNView上放置一个节点，并且我能够在50％的时间内成功完成此操作。另一半时间，屏幕上没有任何内容。我已将其缩小到以下代码行：

func getCameraTransform(for camera: ARCamera) -> MDLTransform {
        return MDLTransform(matrix: camera.transform)
    }

当屏幕上没有显示任何内容时，上述功能将返回 float3（0.0,0.0,0.0）的 transform.translation

我已经检查过，camera.transform提供的值似乎是 simd_float4x4（[[0.98134,0.0198354，-0.191256,0.0）]，[ - 0.0129627,0.998227,0.0371193,0.0]] ，[0.191844，-0.0339474,0.980838,0.0）]，[ - 0.482363，-0.00405288，-0.768801,1.0）]]） transform.translation为0.

为什么这有时会返回0但是在我点击的时候工作完全正常？

以下是完整代码：

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard touches.first!.tapCount == 1 else { return }
        let camera = sceneView.session.currentFrame!.camera

    let transform = getCameraTransform(for: camera)
    let boxGeometry = SCNBox(width: 0.1, height: 0.1, length: 0.1, chamferRadius: 0)
    let cube = SCNNode(geometry: boxGeometry)
// SOMETIMES TRANSFORM.TRANSLATION IS JUST 0s
        let position = SCNVector3(
            transform.translation.x,
            transform.translation.y,
            transform.translation.z
            )
        cube.position = position
        sceneView.scene.rootNode.addChildNode(cube)
    }

func getCameraTransform(for camera: ARCamera) -> MDLTransform {
        return MDLTransform(matrix: camera.transform) // this is returning the 0 translation every other time
    }

Answer 1

I think it may be better to look at a different way to approach the issue. I haven't seen that example before and from having a test, it doesn't seem to be what you need.

As such, I will provide you with a few examples which should help you get started.

(1) Place An Object At A Certain Position Based On The Current Frame Of The Camera:

/// Adds An SCNNode 3m Away From The Current Frame Of The Camera
func addNodeInFrontOfCamera(){

 //1. Get The Current Frame Of The Camera
 guard let currentTransform = augmentedRealitySession.currentFrame?.camera.transform else { return }

 //2. Create An SCNNode
 let nodeToAdd = SCNNode()
 let boxGeometry = SCNBox(width: 0.1, height: 0.1, length: 0.1, chamferRadius: 0)
 boxGeometry.firstMaterial?.diffuse.contents = UIColor.red
 nodeToAdd.geometry = boxGeometry

 // Create A Transform With A Translation 1m In Front Of The Camera
 var translation = matrix_identity_float4x4

 //Change The X Value
 translation.columns.3.x = 0

 //Change The Y Value
 translation.columns.3.y = 0

 //Change The Z Value
 translation.columns.3.z = -1

nodeToAdd.simdTransform = matrix_multiply(currentTransform, translation)
augmentedRealityView?.scene.rootNode.addChildNode(nodeToAdd)

}

(2) Place an SCNNode Based On Any Available featurePoints In The Scene:

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {

    //1. Get The Current Touch Point
    guard let currentTouchPoint = touches.first,
        //2. Perform A Hit Test Against Any Feature Points
        let result = augmentedRealityView.hitTest(currentTouchPoint.location(in: augmentedRealityView), types: .featurePoint).last else { return }

    //3. Get The World Coordinates Of The Result
    let transform = SCNMatrix4(result.worldTransform)

    //4. Get The Positional Data From The Transform
    let vectorFromTransform = SCNVector3(transform.m41, transform.m42, transform.m43)

    //5. Create An SCNBox At The Point
    let boxNode = SCNNode()
    let boxGeometry = SCNBox(width: 0.1, height: 0.1, length: 0.1, chamferRadius: 0)
    boxNode.geometry = boxGeometry
    boxNode.position = vectorFromTransform
    augmentedRealityView.scene.rootNode.addChildNode(boxNode)

}

Apologies if it doesn't explain the results your are experiencing, but nonetheless, I hope it helps...

为什么ARKit MDLTransform从相机变换中随机返回0？

1 个答案: