//屏幕上的点转化为场景中的点
    func convertToScenOf(point: CGPoint) -> SCNVector3{
        let Z_Far:CGFloat = 1 + CGFloat(randomFloat(min: 0.0, max: 1.0))
        var Screen_Aspect : CGFloat = UIScreen.main.bounds.size.width > 400 ? 0.3 : 0.0
        // 计算屏幕边缘的距离
        let Y = tan(Double(self.sceneView.pointOfView!.camera!.fieldOfView/180/2)*Double.pi) * Double(Z_Far-Screen_Aspect)
        let X = tan(Double(self.sceneView.pointOfView!.camera!.fieldOfView/2/180)*Double.pi) * Double(Z_Far-Screen_Aspect) * Double(self.sceneView.bounds.size.width/self.sceneView.bounds.size.height)
        let alphaX = 2 *  CGFloat(X) / self.sceneView.bounds.size.width
        let alphaY = 2 *  CGFloat(Y) / self.sceneView.bounds.size.height
        let x = -CGFloat(X) + point.x * alphaX
        let y = CGFloat(Y) - point.y * alphaY
        let target = SCNVector3Make(Float(x), Float(y), Float(-Z_Far))
        return self.sceneView.pointOfView!.convertPosition(target, to:self.sceneView.scene.rootNode)
    }