我正在开发一款Vision应用程序，它结合了ARKit来测量距离。我在使用Vision跟踪导致VNSequenceRequestHandler的结果为空的对象时遇到了错误。我将包含视图控制器的代码。请注意，其中大部分内容基于在线提供的示例代码。
import UIKit
import SceneKit
import ARKit
import Vision
class ViewController: UIViewController, ARSCNViewDelegate {
@IBOutlet weak var highlightView: UIView!
var sceneSphere = SCNNode()
@IBOutlet var sceneView: ARSCNView!
private var lastObservation: VNDetectedObjectObservation?
private let visionSequenceHandler = VNSequenceRequestHandler()
override func viewDidLoad() {
super.viewDidLoad()
// Set the view's delegate
sceneView.delegate = self
// Show statistics such as fps and timing information
sceneView.showsStatistics = true
// Create a new scene
let scene = SCNScene(named: "art.scnassets/VisionScene.scn")!
// Set the scene to the view
sceneView.scene = scene
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
// Create a session configuration
let configuration = ARWorldTrackingConfiguration()
// Run the view's session
sceneView.session.run(configuration)
sceneSphere = (sceneView.scene.rootNode.childNode(withName: "sphere", recursively: false))!
sceneSphere.scale = SCNVector3.init(0.5, 0.5, 0.5)
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
// Pause the view's session
sceneView.session.pause()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Release any cached data, images, etc that aren't in use.
}
// MARK: - ARSCNViewDelegate
/*
// Override to create and configure nodes for anchors added to the view's session.
func renderer(_ renderer: SCNSceneRenderer, nodeFor anchor: ARAnchor) -> SCNNode? {
let node = SCNNode()
return node
}
*/
@IBAction func userTapped(_ sender: UITapGestureRecognizer) {
//print(sceneView.hitTest(sender.location(in: sceneView), types: ARHitTestResult.ResultType.featurePoint))
print(sender.location(ofTouch: 0, in: view))
let newRect = CGRect(x: (sender.location(ofTouch: 0, in: sceneView)).x, y: (sender.location(ofTouch: 0, in: sceneView)).y, width: 100, height: 100)
highlightView.frame = newRect
let newObservation = VNDetectedObjectObservation(boundingBox: newRect)
sceneSphere.position.x = Float(newObservation.boundingBox.midX)
sceneSphere.position.y = Float(newObservation.boundingBox.midY)
self.lastObservation = newObservation
}
func session(_ session: ARSession, didFailWithError error: Error) {
// Present an error message to the user
}
func sessionWasInterrupted(_ session: ARSession) {
// Inform the user that the session has been interrupted, for example, by presenting an overlay
}
func sessionInterruptionEnded(_ session: ARSession) {
// Reset tracking and/or remove existing anchors if consistent tracking is required
}
}
extension ViewController: SCNSceneRendererDelegate {
func renderer(_ renderer: SCNSceneRenderer, updateAtTime time: TimeInterval) {
//print("updateFrame1")
guard
// make sure the pixel buffer can be converted
let pixelBuffer = (sceneView.session.currentFrame?.capturedImage),
// make sure that there is a previous observation we can feed into the request
let lastObservation = self.lastObservation
else {print("nolastrequest"); return }
print("lO2:\(lastObservation)")
print("lO3:\(lastObservation.boundingBox)")
print(pixelBuffer)
let request = VNTrackObjectRequest(detectedObjectObservation: lastObservation, completionHandler: self.handleVisionRequestUpdate)
// set the accuracy to high
// this is slower, but it works a lot better
request.trackingLevel = .accurate
do {
print(pixelBuffer)
print(request)
try self.visionSequenceHandler.perform([request], on: pixelBuffer)
} catch {
print("Throws: \(error)")
}
}
private func handleVisionRequestUpdate(_ request: VNRequest, error: Error?) {
print("HandleVisionRequest")
print(request.results?.first)
print(request)
// 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
print("lO1:\(request.results?.first)")
print("nORC: \(request.results)")
//let newObservation = request.results?.first as! VNDetectedObjectObservation
//print(newObservation.boundingBox.midX)
//print(self.lastObservation?.boundingBox.midX)
// prepare for next loop
if request.results?.first != nil {
self.lastObservation = newObservation
}
// check the confidence level before updating the UI
/* guard newObservation.confidence >= 0.3 else {
// hide the rectangle when we lose accuracy so the user knows something is wrong
self.highlightView?.frame = .zero
return
}*/
// calculate view rect
//var transformedRect = newObservation.boundingBox
//transformedRect.origin.y = 1 - transformedRect.origin.y
// let convertedRect = self.cameraLayer.layerRectConverted(fromMetadataOutputRect: transformedRect)
/*// move the highlight view
let xChange = ((self.highlightView?.frame.midX)!-convertedRect.midX)
let yChange = ((self.highlightView?.frame.midY)!-convertedRect.midY)
var inchChange = ((xChange + yChange)/72)
inchChange = abs(round(inchChange*60))
print(inchChange)
self.speedLabal.text = "\(inchChange) In/sec"*/
//self.highlightView?.frame = convertedRect
}
}
}
如果我在self.lastObservation = newObservation中禁用了行handleVisionRequestUpdate，则不会发生此错误，但应用程序无法按预期运行。
每当问题发生时，print("nORC: \(request.results)")的结果为nil。我可以上传整个项目，如果这将有所帮助。我会对此提出任何反馈意见。提前谢谢！
答案 0 :(得分：1)
与UIKit相比，Vision Framework使用不同的坐标系。 UIKit的起源位于左上角，最大宽度和高度值是屏幕大小的点数。 但是，Vision Framework的原点位于左下角，宽度和高度的最大值为1。 这就是您的代码无法正常工作的原因。
将lastObservation.boundingBox属性转换为UIKit坐标，然后再将其传递给VNTrackObjectRequest。