ARImageAnchor转换矩阵的坐标与ARPlaneAnchor的坐标相差太大

Question

我正在做这个简单的事情：

1. 垂直平面检测
2. 垂直平面上的图像识别

图像被挂在检测到的平面上（在我的墙上）。在这两种情况下，我都实现的renderer:didAddNode:forAnchor:功能ARSCNViewDelegate。我站在垂直平面检测和图像识别的地方。

func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {
    guard let shipScene = SCNScene(named: "ship.scn"), let shipNode = shipScene.rootNode.childNode(withName: "ship", recursively: false) else { return }
    shipNode.position = SCNVector3(anchor.transform.columns.3.x, anchor.transform.columns.3.y, anchor.transform.columns.3.z)
    sceneView.scene.rootNode.addChildNode(shipNode)
    print(anchor.transform)
}

在垂直平面检测的情况下，anchor将为ARPlaneAnchor。在图像识别的情况下，anchor将为ARImageAnchor。

为什么这两个锚点的转换矩阵如此不同？我正在打印anchor.transform并得到以下结果：

1。

simd_float4x4([
    [0.941312,  0.0,        -0.337538,  0.0)],
    [0.336284,  -0.0861278, 0.937814,   0.0)],
    [-0.0290714,-0.996284,  -0.0810731, 0.0)],
    [0.191099,  0.172432,   -1.14543,   1.0)]
])

2。

simd_float4x4([
    [0.361231,  0.10894,    0.926093,   0.0)],
    [-0.919883, -0.121052,  0.373049,   0.0)],
    [0.152743,  -0.986651,  0.0564843,  0.0)],
    [75.4418,   10.9618,    -14.3788,   1.0)]
])

因此，如果我想在检测到的垂直平面上放置3D对象，我可以简单地[x = 0.191099, y = 0.172432, z = -1.14543]用作坐标来设置节点（myNode）的位置，然后将该节点添加到场景中，sceneView.scene.rootNode.addChildNode(myNode)但是如果我想将3D对象放置在场景中检测到图像的锚点，我无法使用[x = 75.4418, y = 10.9618, z = -14.3788]。

如何将3D对象放置在检测到的图像的锚点上？我真的不明白ARImageAnchor的转换矩阵。

Answer 1

这是您使用该func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor)方法的示例：

func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {

    //1. If Out Target Image Has Been Detected Than Get The Corresponding Anchor
    guard let currentImageAnchor = anchor as? ARImageAnchor else { return }

    let x = currentImageAnchor.transform
    print(x.columns.3.x, x.columns.3.y , x.columns.3.z)

    //2. Get The Targets Name
    let name = currentImageAnchor.referenceImage.name!

    //3. Get The Targets Width & Height In Meters
    let width = currentImageAnchor.referenceImage.physicalSize.width
    let height = currentImageAnchor.referenceImage.physicalSize.height

    print("""
    Image Name = \(name)
    Image Width = \(width)
    Image Height = \(height)
    """)

    //4. Create A Plane Geometry To Cover The ARImageAnchor
    let planeNode = SCNNode()
    let planeGeometry = SCNPlane(width: width, height: height)
    planeGeometry.firstMaterial?.diffuse.contents = UIColor.white
    planeNode.opacity = 0.25
    planeNode.geometry = planeGeometry

    //5. Rotate The PlaneNode To Horizontal
    planeNode.eulerAngles.x = -.pi/2

    //The Node Is Centered In The Anchor (0,0,0)
    node.addChildNode(planeNode)


    //6. Create AN SCNBox
    let boxNode = SCNNode()
    let boxGeometry = SCNBox(width: 0.1, height: 0.1, length: 0.1, chamferRadius: 0)

    //7. Create A Different Colour For Each Face
    let faceColours = [UIColor.red, UIColor.green, UIColor.blue, UIColor.cyan, UIColor.yellow, UIColor.gray]
    var faceMaterials = [SCNMaterial]()

    //8. Apply It To Each Face
    for face in 0 ..< 5{
        let material = SCNMaterial()
        material.diffuse.contents = faceColours[face]
        faceMaterials.append(material)
    }
    boxGeometry.materials = faceMaterials
    boxNode.geometry = boxGeometry

    //9. Set The Boxes Position To Be Placed On The Plane (node.x + box.height)
    boxNode.position = SCNVector3(0 , 0.05, 0)

    //10. Add The Box To The Node
    node.addChildNode(boxNode)


}

根据我的理解（我当然可以错了），您会知道您的放置区域就是referenceImage.physicalSize以米为单位的宽度和高度：

let width = currentImageAnchor.referenceImage.physicalSize.width
let height = currentImageAnchor.referenceImage.physicalSize.height

因此，假设您希望内容看起来像覆盖图像，则需要在这些边界内缩放内容（如果需要适应）。