初始化模型,位置为 SCNVector3(0, -1, -2), 对于大的模型, 初始化后不容易被用户找到, 所以初始化时让模型全貌的显示在屏幕前方

lazy var node: AudioinARKitLocationNode = {
    
    let modelScene = SCNScene(named: scnName)!
    let cup = modelScene.rootNode.childNodes[0]
    let node = AudioinARKitLocationNode(location: location, node: cup)
    node.name = scnName
    let boundingBox = node.boundingBox
    let distance = boundingBox.max.distance(to: boundingBox.min)
    let base: Float = 0.8
    if distance > base {
        // 缩放模型, 初始化时,不超出屏幕大小
        let scale = base / distance
        node.scale = SCNVector3(scale, scale, scale)
    }
    return node
    
}()
extension SCNVector3 {
    func distance(to anotherVector: SCNVector3) -> Float {
        return sqrt(pow(anotherVector.x - x, 2) + pow(anotherVector.z - z, 2))
    }    
}