相机不在Scenekit中跟随飞机

Question

我有一架我正在追踪的飞行飞机，我也在展示飞机所遵循的路径。 我正在绘制圆柱作为绘制路径的线。 它在2点之间画一条线。 我有一个cameraNode，最初设置为（0,200,200）。 那时我可以看到飞机。 但是当我开始飞行时。 它离开了屏幕。 我想要两件事：

1. 跟随飞机（路径无关紧要）。
2. 显示整条路径以及飞机。

我尝试找到min ad max x，y和z并取平均值，但它不起作用。 如果你看到下面的gif，它太快了，飞机已经移出屏幕了

以下是我设置相机的方法：

- (void)setUpCamera {
SCNScene *workingScene = [self getWorkingScene];
_cameraNode = [[SCNNode alloc] init];
_cameraNode.camera = [SCNCamera camera];
_cameraNode.camera.zFar = 500;
_cameraNode.position = SCNVector3Make(0, 60, 50);
[workingScene.rootNode addChildNode:_cameraNode];

SCNNode *frontCameraNode = [SCNNode node];
frontCameraNode.position = SCNVector3Make(0, 100, 50);
frontCameraNode.camera = [SCNCamera camera];
frontCameraNode.camera.xFov = 75;
frontCameraNode.camera.zFar = 500;
[_assetActivity addChildNode:frontCameraNode]; //_assetActivity is the aircraft node.

}

这是我如何改变不起作用的相机位置：

- (void)showRealTimeFlightPath {


DAL3DPoint *point = [self.aircraftLocation convertCooridnateTo3DPoint];
DAL3DPoint *previousPoint = [self.previousAircraftLocation convertCooridnateTo3DPoint];
self.minCoordinate = [self.minCoordinate findMinPoint:self.minCoordinate currentPoint:point];
self.maxCoordinate = [self.minCoordinate findMaxPoint:self.maxCoordinate currentPoint:point];
DAL3DPoint *averagePoint = [[DAL3DPoint alloc] init];
averagePoint = [averagePoint averageBetweenCoordiantes:self.minCoordinate maxPoint:self.maxCoordinate];

SCNVector3 positions[] = {
    SCNVector3Make(point.x,point.y,point.z) ,
    SCNVector3Make(previousPoint.x,previousPoint.y,previousPoint.z)
};
SCNScene *workingScene = [self getWorkingScene];
DALLineNode *lineNodeA = [[DALLineNode alloc] init];
[lineNodeA init:workingScene.rootNode v1:positions[0] v2:positions[1] radius:0.1 radSegementCount:6 lineColor:[UIColor greenColor]] ;
[workingScene.rootNode addChildNode:lineNodeA];
self.previousAircraftLocation = [self.aircraftLocation mutableCopy];
self.cameraNode.position = SCNVector3Make(averagePoint.x, averagePoint.y, z);
self.pointOfView = self.cameraNode;

}

我们欢迎快速或客观的代码。

谢谢！！

Answer 1

您描述的第一个行为最容易通过链接观察约束和距离约束来实现，两者都是针对飞机的。

let lookAtConstraint = SCNLookAtConstraint(target: aircraft)

let distanceConstraint = SCNDistanceConstraint(target: aircraft)
distanceConstraint.minimumDistance = 10 // set to whatever minimum distance between the camera and aircraft you'd like
distanceConstraint.maximumDistance = 10 // set to whatever maximum distance between the camera and aircraft you'd like

camera.constraints = [lookAtConstraint, distanceConstraint]

对于iOS 10及更早版本，您可以使用SCNTransformConstraint实现距离约束。 这是一个基本的（虽然有点丑😛）实现，它使用线性插值来更新节点的位置。

func normalize(_ value: Float, in range: ClosedRange<Float>) -> Float {
    return (value - range.lowerBound) / (range.upperBound - range.lowerBound)
}

func interpolate(from start: Float, to end: Float, alpha: Float) -> Float {
    return (1 - alpha) * start + alpha * end
}

let target = airplane

let minimumDistance: Float = 10
let maximumDistance: Float = 15

let distanceConstraint = SCNTransformConstraint(inWorldSpace: false) { (node, transform) -> SCNMatrix4 in
    let distance = abs(sqrt(pow(target.position.x - node.position.x, 2) + pow(target.position.y - node.position.y, 2) + pow(target.position.z - node.position.z, 2)))

    let normalizedDistance: Float

    switch distance {
    case ...minimumDistance:
        normalizedDistance = self.normalize(minimumDistance, in: 0 ... distance)
    case maximumDistance...:
        normalizedDistance = self.normalize(maximumDistance, in: 0 ... distance)
    default:
        return transform
    }

    node.position.x = self.interpolate(from: target.position.x, to: node.position.x, alpha: normalizedDistance)
    node.position.y = self.interpolate(from: target.position.y, to: node.position.y, alpha: normalizedDistance)
    node.position.z = self.interpolate(from: target.position.z, to: node.position.z, alpha: normalizedDistance)

    return transform
}

第二种行为可以通过确定飞机的边界框及其在摄像机局部坐标空间中的所有路径段来实现，然后更新摄像机距该边界框中心的距离，以构建视口中的所有节点。 frameNodes(_:)是一种实现此功能的便捷方法，在iOS 11中引入并在SCNCameraController上定义。 我建议尽可能使用它，除非你想自己深入研究三角学。 您可以使用场景视图的默认摄像头控制器或创建一个临时实例，以满足您的应用程序的需要。

Answer 2

您需要计算速度的角度，以便摄像机指向移动SCNNode的方向。

此代码将指向正确的方向。

    func renderer(_ aRenderer: SCNSceneRenderer, didSimulatePhysicsAtTime time: TimeInterval) {

        // get velocity angle using velocity of vehicle

        var degrees = convertVectorToAngle(vector: vehicle.chassisBody.velocity)

        // get rotation of current camera on X and Z axis

        let eX = cameraNode.eulerAngles.x
        let eZ = cameraNode.eulerAngles.z

        // offset rotation on y axis by 90 degrees

        // this needs work, buggy

        let ninety = deg2rad(90)

        // default camera Y Euler angle facing north at 0 degrees

        var eY : Float = 0.0

        if degrees != 0 {

            eY = Float(-degrees) - Float(ninety)

        }

        // rotate camera direction using cameraNode.eulerAngles and direction of velocity as eY

        cameraNode.eulerAngles = SCNVector3Make(eX, eY, eZ)

        // put camera 25 points behind vehicle facing direction of velocity

        let dir = calculateCameraDirection(cameraNode: vehicleNode)
        let pos = pointInFrontOfPoint(point: vehicleNode.position, direction:dir, distance: 25)

        // camera follows driver view from 25 points behind, and 10 points above vehicle

        cameraNode.position = SCNVector3Make(pos.x, vehicleNode.position.y + 10, pos.z)

}

func convertVectorToAngle(vector: SCNVector3) -> CGFloat {

    let degrees = atan2(vector.z, vector.x)

    return CGFloat(degrees)

}


func pointInFrontOfPoint(point: SCNVector3, direction: SCNVector3, distance: Float) -> SCNVector3 {

    var x = Float()
    var y = Float()
    var z = Float()

    x = point.x + distance * direction.x
    y = point.y + distance * direction.y
    z = point.z + distance * direction.z

    let result = SCNVector3Make(x, y, z)
    return result

}

func calculateCameraDirection(cameraNode: SCNNode) -> SCNVector3 {

            let x = -cameraNode.rotation.x
            let y = -cameraNode.rotation.y
            let z = -cameraNode.rotation.z
            let w = cameraNode.rotation.w
            let cameraRotationMatrix = GLKMatrix3Make(cos(w) + pow(x, 2) * (1 - cos(w)),
                                                      x * y * (1 - cos(w)) - z * sin(w),
                                                      x * z * (1 - cos(w)) + y*sin(w),

                                                      y*x*(1-cos(w)) + z*sin(w),
                                                      cos(w) + pow(y, 2) * (1 - cos(w)),
                                                      y*z*(1-cos(w)) - x*sin(w),

                                                      z*x*(1 - cos(w)) - y*sin(w),
                                                      z*y*(1 - cos(w)) + x*sin(w),
                                                      cos(w) + pow(z, 2) * ( 1 - cos(w)))

            let cameraDirection = GLKMatrix3MultiplyVector3(cameraRotationMatrix, GLKVector3Make(0.0, 0.0, -1.0))
            return SCNVector3FromGLKVector3(cameraDirection)
}

func deg2rad(_ number: Double) -> Double {

        return number * .pi / 180

}