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。