SCNVector3 到 2D 箭头方向的 SCNVector3

Question

我正在使用 ARKit

我有相机 x、y、z（笛卡尔坐标）和 3D 对象 x、y、z。我试图在 2D (x,y) 中指向一个箭头 (UIImageView) 以显示相机应该移动的位置，以便用户看到 3D 对象。

我已经尝试使用下面的代码使用反正切函数（向量的方向）计算箭头的方向，但我怀疑坐标系有问题

func redirectArrow(bee: SCNNode, arrow: UIImageView) {
    
    let (direction, position) = self.getUserVector()

    let dx = bee.position.x - position.x
    let dy = bee.position.y - position.y

    let arctangent = atan(dy/dx)

    arrow.transform = CGAffineTransform(rotationAngle: CGFloat(arctangent))
    
    DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) {
        self.redirectArrow(bee: bee, arrow: arrow)
    }
    
}

getUserVector()的代码

func getUserVector() -> (SCNVector3, SCNVector3) { // (direction, position)
    if let frame = self.sceneView.session.currentFrame {
        let mat = SCNMatrix4(frame.camera.transform) // 4x4 transform matrix describing camera in world space
        let dir = SCNVector3(-1 * mat.m31, -1 * mat.m32, -1 * mat.m33) // orientation of camera in world space
        let pos = SCNVector3(mat.m41, mat.m42, mat.m43) // location of camera in world space
        
        return (dir, pos)
    }
    return (SCNVector3(0, 0, -1), SCNVector3(0, 0, -0.2))
}

更新

感谢 mnuages 回答，箭头现在使用下面的代码指向 3D 对象

func redirectArrow(bee: SCNNode, arrow: UIImageView) {
    
    let (direction, position) = self.getUserVector()
    
    let bee2DPosition = sceneView.projectPoint(bee.position)
    let world2DPosition = sceneView.projectPoint(direction)
    
    let dx = bee2DPosition.x - world2DPosition.x
    let dy = bee2DPosition.y - world2DPosition.y

    var arctangent: Float = atan(dy/dx)
    
    if dx < 0 {
        arctangent += Float(Double.pi)
    }

    arrow.transform = CGAffineTransform(rotationAngle: CGFloat(arctangent))
    
    DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) {
        self.redirectArrow(bee: bee, arrow: arrow)
    }
    
}

Answer 1

projectPoint(_:)API就是您所需要的：

Projects a point from the 3D world coordinate system of the scene to the 2D pixel coordinate system of the renderer.

SCNVector3 到 2D 箭头方向的 SCNVector3

SCNVector3 to SCNVector3 in 2D arrow direction

scenekit

swift

arkit