如何将视觉框架坐标系转换为ARKit？

Question

我正在使用ARKit(使用SceneKit)添加虚拟对象(例如球).我通过使用Vision框架并在视觉请求完成处理程序方法中接收其更新位置来跟踪真实世界对象(例如,脚).

let request = VNTrackObjectRequest(detectedObjectObservation: lastObservation, completionHandler: self.handleVisionRequestUpdate)

我想用虚拟替换跟踪的现实世界对象(例如用立方体替换脚)但是我不知道如何将边界框矩形(我们在视觉请求完成中接收)替换为场景套件节点,因为坐标系统是不同的.

以下是视觉请求完成处理程序的代码:

 private func handleVisionRequestUpdate(_ request: VNRequest, error: Error?) {
    // Dispatch to the main queue because we are touching non-atomic, non-thread safe properties of the view controller
    DispatchQueue.main.async {
      // make sure we have an actual result
      guard let newObservation = request.results?.first as? VNDetectedObjectObservation else { return }

      // prepare for next loop
      self.lastObservation = newObservation

      // check the confidence level before updating the UI
      guard newObservation.confidence >= 0.3 else {
        return
      }

      // calculate view rect
      var transformedRect = newObservation.boundingBox

     //How to convert transformedRect into AR Coordinate
  self.node.position = SCNVector3Make(?.worldTransform.columns.3.x,
    ?.worldTransform.columns.3.y,

    }
  }

请指导我转移坐标系.

Answer 1

假设矩形位于水平平面上,您可以对所有4个角上的场景执行命中测试,并使用其中3个角来计算矩形的宽度,高度,中心和方向.

我在GitHub上有一个可用的演示应用程序:https: //github.com/mludowise/ARKitRectangleDetection

矩形角的坐标VNRectangleObservation将相对于图像的大小和不同的坐标,具体取决于手机的旋转.您需要将它们乘以视图大小并根据手机的旋转将它们反转:

func convertFromCamera(_ point: CGPoint, view sceneView: ARSCNView) -> CGPoint {
    let orientation = UIApplication.shared.statusBarOrientation

    switch orientation {
    case .portrait, .unknown:
        return CGPoint(x: point.y * sceneView.frame.width, y: point.x * sceneView.frame.height)
    case .landscapeLeft:
        return CGPoint(x: (1 - point.x) * sceneView.frame.width, y: point.y * sceneView.frame.height)
    case .landscapeRight:
        return CGPoint(x: point.x * sceneView.frame.width, y: (1 - point.y) * sceneView.frame.height)
    case .portraitUpsideDown:
        return CGPoint(x: (1 - point.y) * sceneView.frame.width, y: (1 - point.x) * sceneView.frame.height)
    }
}

然后你可以对所有4个角进行命中测试..existingPlaneUsingExtent在执行命中测试时使用该类型非常重要,以便ARKit返回水平平面的命中.

let tl = sceneView.hitTest(convertFromCamera(rectangle.topLeft, view: sceneView), types: .existingPlaneUsingExtent)
let tr = sceneView.hitTest(convertFromCamera(rectangle.topRight, view: sceneView), types: .existingPlaneUsingExtent)
let bl = sceneView.hitTest(convertFromCamera(rectangle.bottomLeft, view: sceneView), types: .existingPlaneUsingExtent)
let br = sceneView.hitTest(convertFromCamera(rectangle.bottomRight, view: sceneView), types: .existingPlaneUsingExtent)

然后它变得有点复杂......

因为每个命中测试都可以返回0到n的结果,所以您需要过滤掉不同平面上包含的任何命中测试.你可以通过比较每个锚点来做到这一点ARHitTestResult:

hit1.anchor == hit2.anchor

此外,您只需要4个角中的3个来识别矩形的尺寸,位置和方向,这样如果一个角不返回任何命中测试结果就可以了.看看这里,因为我是怎么做的.

您可以根据左右角之间的距离(顶部或底部)计算矩形的宽度.同样,您可以根据顶角和底角之间的距离(左侧或右侧)计算矩形的高度.

func distance(_ a: SCNVector3, from b: SCNVector3) -> CGFloat {
    let deltaX = a.x - b.x
    let deltaY = a.y - b.y
    let deltaZ = a.z - b.z

    return CGFloat(sqrt(deltaX * deltaX + deltaY * deltaY + deltaZ * deltaZ))
}

let width = distance(right, from: left)
let height = distance(top, from: bottom)

您可以通过从矩形的相对角(topLeft&bottomRight或topRight&bottomLeft)获取中点来计算其位置:

let midX = (c1.x + c2.x) / 2
let midY = (c1.y + c2.y) / 2
let midZ = (c1.z + c2.z) / 2
let center = SCNVector3Make(midX, midY, midZ)

您还可以从左右角(顶部或底部)计算矩形的方向(沿y轴旋转):

let distX = right.x - left.x
let distZ = right.z - left.z
let orientation = -atan(distZ / distX)

然后将它们全部放在一起并在矩形上显示AR中的某些内容.这是通过子类化显示虚拟矩形的示例SCNNode:

class RectangleNode: SCNNode {

    init(center: SCNVector3, width: CGFloat, height: CGFloat, orientation: Float) {
        super.init()

        // Create the 3D plane geometry with the dimensions calculated from corners
        let planeGeometry = SCNPlane(width: width, height: height)
        let rectNode = SCNNode(geometry: planeGeometry)

        // Planes in SceneKit are vertical by default so we need to rotate
        // 90 degrees to match planes in ARKit
        var transform = SCNMatrix4MakeRotation(-Float.pi / 2.0, 1.0, 0.0, 0.0)

        // Set rotation to the corner of the rectangle
        transform = SCNMatrix4Rotate(transform, orientation, 0, 1, 0)

        rectNode.transform = transform

        // We add the new node to ourself since we inherited from SCNNode
        self.addChildNode(rectNode)

        // Set position to the center of rectangle
        self.position = center
    }
}