为什么 ARKit MDLTransform 从相机变换中随机 return 0？

Question

我是 ARKit 的新手（准确地说是 2 天前），我试图在点击时在我的 ARSCNView 上放置一个节点，并且我能够在 50% 的时间内成功地这样做。另一半时间，屏幕上什么也没有出现。我已将其缩小为以下代码行：

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

当屏幕上什么都没有出现时，上面的函数是 returning transform.translation of float3(0.0, 0.0, 0.0)

我已经检查过 camera.transform 提供的值看起来像 simd_float4x4([[0.98134, 0.0198354, -0.191256, 0.0)], [-0.0129627 , 0.999227, 0.0371193, 0.0)], [0.191844, -0.0339474, 0.980838, 0.0)], [-0.482363, -0.00405288, -0.768801, 1.0)]]) transform.translation 为 0.

为什么这个 return 0 有时在我点击时却工作得很好？

完整代码如下：

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

我认为换一种方式来解决这个问题可能会更好。我之前和测试都没有看到那个例子，它似乎不是你需要的。

因此，我将为您提供一些示例，以帮助您入门。

(1)根据相机当前帧将物体放置在某个位置：

/// 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) 根据场景中任何可用的特征点放置一个 SCNNode：

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)

}

如果它不能解释您所经历的结果，我们深表歉意，但尽管如此，我希望它能有所帮助...

为什么 ARKit MDLTransform 从相机变换中随机 return 0？

Why does ARKit MDLTransform randomly return 0 from camera transform?

ios

swift

arkit