ARImageAnchor 变换矩阵的坐标与 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

图像挂在检测到的平面上（在我的墙上）。在这两种情况下，我都从ARSCNViewDelegate 实现了renderer:didAddNode:forAnchor: 函数。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 将是ARPlaneAnchor。在图像识别的情况下，anchor 将是 ARImageAnchor。

为什么这两个锚的变换矩阵如此不同？我正在打印anchor.transform，我得到了这些结果：

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)]
])

所以如果我想在检测到的垂直平面上放置一个 3D 对象，我可以简单地使用[x = 0.191099, y = 0.172432, z = -1.14543] 作为坐标来设置我的节点（myNode）的位置，然后使用@987654334 将此节点添加到场景中@ 但是如果我想在检测到的图像的锚点上放置一个 3D 对象，我不能使用[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 的变换矩阵。

Answer 1

这是我使用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）你会知道你的放置区域是referenceImage.physicalSize的宽度和高度，以米表示：

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

因此，您需要在这些边界内缩放您的内容（如果需要适合），假设您希望它看起来覆盖图像。