概述

ARKit 2.0发布以来，iOS端AR类应用层出不穷。由于其强大的功能，许多人们对于AR应用的美好设想都一一实现。
AR（Augmented Reality）的最初定义，就是增强现实（或扩增现实），即在外部设备的辅助下增强现实生活的感官体验。AR的本质也是虚拟，是在现实世界之上叠加虚拟场景以提供更加直观或有趣的信息。
基于这一定义，人们很容易想到利用AR看到周边街景中被遮挡的部分，并显示其基本信息的应用场景。利用手机这一外部辅助设备，内置摄像头捕捉到的画面就是现实景观，开发者可以在摄像头的实景之上添加想要添加的3D标注，并附以有用的信息，简单的AR导航就得能以实现。

基础

该功能的实现核心是基于CoreLocation的实时定位功能与ARKit的图层的结合。实现的基础除ARKit和iOS 11.0+以外，还借鉴了GitHub开源项目ARKit+CoreLocation提供的ARCL工具类，建议首先仔细阅读此项目中源码，领悟实现思想和逻辑。

实现

前期准备工作

项目中代码使用Swift 4.2 编写。
1.首先，在项目中引入上文中提到的 ARCL中的Source部分，或者直接pod ‘ARCL’。
其中各文件中代码的作用可以从他们的命名中一目了然，这里就不做赘述，参见以下文件目录结构：

Source
├── CGPoint+Extensions.swift
├── CLLocation+Extensions.swift
├── FloatingPoint+Radians.swift
├── LocationManager.swift
├── LocationNode.swift
├── SCNNode+Extensions.swift
├── SCNVector3+Extensions.swift
├── SceneLocationEstimate+Extensions.swift
├── SceneLocationEstimate.swift
└── SceneLocationView.swift

2.在Plist中加入NSCameraUsageDescription和NSLocationWhenInUseUsageDescription的key并添加简短描述。

改写ARCL中的LocationNode.swift,即构造你需要的标注样式和内容。

open class LocationAnnotationNode: LocationNode {
    ///An image to use for the annotation
    ///When viewed from a distance, the annotation will be seen at the size provided
    ///e.g. if the size is 100x100px, the annotation will take up approx 100x100 points on screen.
    public let image: UIImage

    ///Subnodes and adjustments should be applied to this subnode
    ///Required to allow scaling at the same time as having a 2D 'billboard' appearance
    public let annotationNode: SCNNode

    ///Whether the node should be scaled relative to its distance from the camera
    ///Default value (false) scales it to visually appear at the same size no matter the distance
    ///Setting to true causes annotation nodes to scale like a regular node
    ///Scaling relative to distance may be useful with local navigation-based uses
    ///For landmarks in the distance, the default is correct
    public var scaleRelativeToDistance = false


    public init(location: CLLocation?, image: UIImage, title: String, distance: String) {
        self.image = image

        let frame: CGRect = CGRect(x:0.0, y:0.0, width:200.0, height:82.0)
        let bgImageView = UIImageView.init(frame: frame)
        bgImageView.image = image

        let titleLabel = UILabel.init(frame: CGRect(x: 0.0, y: 0.0, width: 120.0, height: 60.0))
        titleLabel.textColor = UIColor.darkText
        titleLabel.font = UIFont.boldSystemFont(ofSize: 18.0)
        titleLabel.text = title
        titleLabel.textAlignment = NSTextAlignment.center
        bgImageView.addSubview(titleLabel)

        let distanceLabel = UILabel.init(frame: CGRect(x: 120.0, y: 0.0, width: 80.0, height: 60.0))
        distanceLabel.textColor = UIColor.init(red: 19.0/255.0, green: 115.0/255.0, blue: 114.0/255.0, alpha: 1.0)
        distanceLabel.font = UIFont.systemFont(ofSize: 16.0)
        distanceLabel.text = distance
        distanceLabel.textAlignment = NSTextAlignment.center
        bgImageView.addSubview(distanceLabel)


        let plane = SCNPlane(width: frame.size.width/100, height: frame.size.height/100)
        plane.firstMaterial!.diffuse.contents = bgImageView
        plane.firstMaterial!.lightingModel = .constant

        annotationNode = SCNNode()
        annotationNode.geometry = plane

        super.init(location: location)

        self.name = title
        self.distance = distance
        self.distanceLabel = distanceLabel

        let billboardConstraint = SCNBillboardConstraint()
        billboardConstraint.freeAxes = SCNBillboardAxis.Y
        constraints = [billboardConstraint]

        addChildNode(annotationNode)
    }

以上代码的作用是使用位置名称和距离创建标注，返回一个带标题和距离信息的气泡，注意：这里的距离是实时变化的，也就是在初始化时给定一个初始值，而在获取到的位置信息后通过计算实时进行更新，以达到动态更新场景的效果

呈现

在以上准备工作的基础上，我们需要将AR标注实时呈现在摄像头中。
因此我们需要初始化SceneLocationView和MKMapView,并完成相关配置。

初始化sceneLocationView

sceneLocationView.locationDelegate = self as? SceneLocationViewDelegate
        // Set to true to display am arrow wjoch points north.
        sceneLocationView.orientToTrueNorth = false
        sceneLocationView.showAxesNode = true
        if displayDebugging {
            sceneLocationView.showFeaturePoints = true
        }
        buildData().forEach {
            sceneLocationView.addLocationNodeWithConfirmedLocation(locationNode: $0)
        }
        view.addSubview(sceneLocationView)

初始化mapView

if !showMapView {
            mapView.delegate = self as? MKMapViewDelegate
            mapView.showsUserLocation = true
            mapView.isHidden = true
            view.addSubview(mapView)
        }

使用LocationAnnotationNode的init方法创建标注点。

func buildNode(latitude: CLLocationDegrees, longtitude: CLLocationDegrees, altitude: CLLocationDistance, imageName: String, title: String, distance: String) -> LocationAnnotationNode {
        let location = CLLocation(coordinate: CLLocationCoordinate2D(latitude: latitude, longitude: longtitude), altitude: altitude)
        let image = UIImage(named: imageName)!

        return LocationAnnotationNode(location: location, image: image, title: title, distance: distance)
}

再利用定时器连续且间断地更新标注信息。

// Update user location and show distance from current location to nodes added
updateUserLocationTimer = Timer.scheduledTimer(timeInterval: 3.0,
                                                       target: self,
                                                       selector: #selector(ViewController.updateUserLocation),
                                                       userInfo: nil,
                                                       repeats: true)

在适当的时候更新距离信息即可。

@objc func updateUserLocation() {
        guard let currentLocation = sceneLocationView.currentLocation() else {
            return
        }

        DispatchQueue.main.async {
            if let bestEstimate = self.sceneLocationView.bestLocationEstimate(), let position = self.sceneLocationView.currentScenePosition() {
                print("------------------------------------")
                print("Fetch current location")
                print("Best location estimate, position: \(bestEstimate.position), location: \(bestEstimate.location.coordinate), accurace: \(bestEstimate.location.horizontalAccuracy)")
                print("current position: \(position)")

                let translation = bestEstimate.translatedLocation(to: position)
                print("translation: \(translation)")
                print("translated location: \(currentLocation)")
                print("------------------------------------")

                // Location nodes
                for node in self.sceneLocationView.locationNodes {
                    let distance = currentLocation.distance(from: node.location)
                    var distanceStr: String = String(format: "%.0fm", distance)
                    if distance >= 1000 {
                        distanceStr = String(format: "%.1fkm", (distance/1000))
                    }
                    node.distance = distanceStr
                    node.distanceLabel.text = distanceStr
                }
            }
        }
    }

以上。

无忌不悔

ARKit应用之导航

概述

基础

实现

前期准备工作

呈现