相机没有跟随 Scenekit 中的飞机

Question

我有一架飞行的飞机，我正在跟随它，我还展示了飞机所遵循的路径。我正在绘制圆柱体作为绘制路径的线。它有点像在两点之间画一条线。我有一个最初设置为 (0,200,200) 的 cameraNode。那时我可以看到飞机。但是当我开始飞行时。它走出屏幕。我想要两件事：

1. 只跟随飞机（路径无关紧要）。
2. 显示整个路径以及飞机。

我尝试找到最小广告最大 x、y 和 z 并取平均值，但它不起作用。如果你看到下面的 gif 它太放大了，飞机已经移出屏幕

这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.

}

以下是我如何更改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;

}

欢迎使用 swift 或 Objective c 中的代码。

谢谢！！

Answer 1

您描述的第一个行为最容易通过链接查看约束和距离约束来实现，两者都针对飞机。

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（虽然有点难看?）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您的飞机的边界框及其在相机的局部坐标空间中的所有路径段来实现，然后更新相机与该边界框中心的距离以将所有这些节点框在视口。 frameNodes(_:)，一种实现此功能的便捷方法，在 iOS 11 中引入，并在 SCNCameraController 上定义。如果可能，我建议您使用它，除非您想自己深入了解三角学。您可以使用场景视图的默认相机控制器或创建一个临时实例，以适合您的应用程序的需要。

Answer 2

您需要计算速度的角度，以便相机指向移动的 SCNNode 的方向。

此代码将为您指明正确的方向。

    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

}