18

我正在使用 ARKit(带有 SceneKit)来添加虚拟对象(例如球)。我正在通过使用 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现实世界的对象(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),但我不确定如何将 boundingBox rect(我们在视觉请求完成中收到)替换为场景工具包节点,因为坐标系不同。

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。

4

2 回答 2

22

假设矩形在水平面上,您可以对场景的所有 4 个角执行命中测试,并使用其中 3 个角计算矩形的宽度、高度、中心和方向。

我在 GitHub 上有一个演示应用程序可以做到这一点: https ://github.com/mludowise/ARKitRectangleDetection

矩形角的坐标VNRectangleObservation将与图像的大小相关,并且根据手机的旋转在不同的坐标中。您需要将它们乘以视图大小并根据手机的旋转来反转它们:

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)
    }
}

然后您可以对所有 4 个角进行命中测试。在执行命中测试时使用类型很重要,.existingPlaneUsingExtent这样 ARKit 会返回水平面的命中。

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)

然后就有点复杂了...

因为每个命中测试可能会返回 0 到 n 个结果,所以您需要过滤掉包含在不同平面上的任何命中测试。您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,因此如果一个角不返回任何命中测试结果也没关系。看看这里我是怎么做到的。

您可以根据左右角(顶部或底部)之间的距离计算矩形的宽度。同样,您可以根据顶角和底角之间的距离(左或右)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)

然后把它们放在一起,在 AR 中显示一些东西,覆盖在矩形上。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
    }
}
于 2017-08-07T03:46:23.173 回答
3

要考虑的主要事情是边界矩形在 2D 图像中,而 ARKit 的场景是 3D。这意味着在您选择深度之前,不会定义边界矩形在 3D 中的位置。

你应该做的是对场景进行命中测试以从 2D 坐标到 3D:

let box = newObservation.boundingBox
let rectCenter = CGPoint(x: box.midX, y: box.midY)
let hitTestResults = sceneView.hitTest(rectCenter, types: [.existingPlaneUsingExtent, .featurePoint])
// Pick the hitTestResult you need (nearest?), get position via worldTransform
于 2017-07-23T09:05:06.573 回答