Determine if SKNode is in front of camera view (ARKit Spritekit) - ios

Question

I'm trying to detect when the camera is facing my object that I've placed in ARSKView. Here's the code:
override func update(_ currentTime: TimeInterval) {
// Called before each frame is rendered
guard let sceneView = self.view as? ARSKView else {
return
}
if let currentFrame = sceneView.session.currentFrame {
//let cameraZ = currentFrame.camera.transform.columns.3.z
for anchor in currentFrame.anchors {
if let spriteNode = sceneView.node(for: anchor), spriteNode.name == "token", intersects(spriteNode) {
// token is within the camera view
let distance = simd_distance(anchor.transform.columns.3,
currentFrame.camera.transform.columns.3)
//print("DISTANCE BETWEEN CAMERA AND TOKEN: \(distance)")
if distance <= captureDistance {
// token is within the camera view and within capture distance
print("token is within the camera view and within capture distance")
}
}
}
}
}
The problem is that the intersects method is returning true both when the object is directly in front of the camera, as well as directly behind you. How can I update this code so it only detects when the spriteNode is in the current camera viewfinder? I'm using SpriteKit by the way, not SceneKit.
Here's the code I'm using to actually create the anchor:
self.captureDistance = captureDistance
guard let sceneView = self.view as? ARSKView else {
return
}
// Create anchor using the camera's current position
if sceneView.session.currentFrame != nil {
print("token dropped at \(distance) meters and bearing: \(bearing)")
// Add a new anchor to the session
let transform = getTransformGiven(bearing: bearing, distance: distance)
let anchor = ARAnchor(transform: transform)
sceneView.session.add(anchor: anchor)
}
func getTransformGiven(bearing: Float, distance: Float) -> matrix_float4x4 {
let origin = MatrixHelper.translate(x: 0, y: 0, z: Float(distance * -1))
let bearingTransform = MatrixHelper.rotateMatrixAroundY(degrees: bearing * -1, matrix: origin)
return bearingTransform
}

Answer 1

I have spent a while looking at this, and have come to the conclusion that trying to get the distance between the currentFrame.camera and the anchor doesn't work simply because it returns similar values irregardless of whether the anchor is infront of, or behind the camera. By this I mean that if we assume that our anchor is at point x, and we move forwards 1meter or backwards 1 meter, the distance from the camera and the anchor is still 1 meter.
As such after some experimenting I believe we need to look at the following variables and functions to help us detect whether our SKNode is infront of the camera:
(a) The zPosition of the SpriteNode which refers to:
The z-order of the node (used for ordering). Negative z is "into" the screen, Positive z is "out" of the screen
(b) open func intersects(_ node: SKNode) -> Bool which:
Returns true if the bounds of this node intersects with the
transformed bounds of the other node, otherwise false.
As such the following seems to do exactly what you need:
override func update(_ currentTime: TimeInterval) {
//1. Get The Current ARSKView & Current Frame
guard let sceneView = self.view as? ARSKView, let currentFrame = sceneView.session.currentFrame else { return }
//3. Iterate Through Our Anchors & Check For Our Token Node
for anchor in currentFrame.anchors {
if let spriteNode = sceneView.node(for: anchor), spriteNode.name == "token"{
/*
If The ZPosition Of The SpriteNode Is Negative It Can Be Seen As Into The Screen Whereas Positive Is Out Of The Screen
However We Also Need To Know Whether The Actual Frostrum (SKScene) Intersects Our Object
If Our ZPosition Is Negative & The SKScene Doesnt Intersect Our Node Then We Can Assume It Isnt Visible
*/
if spriteNode.zPosition <= 0 && intersects(spriteNode){
print("Infront Of Camera")
}else{
print("Not InFront Of Camera")
}
}
}
}
Hope it helps...

Answer 2

You can also use this function to check the camera's position :-
- (void)session:(ARSession *)session didUpdateFrame:(ARFrame *)frame; {
simd_float4x4 transform = session.currentFrame.camera.transform;
SCNVector3 position = SCNVector3Make(transform.columns[3].x,
transform.columns[3].y,
transform.columns[3].z);
// Call any function to check the Position.
}

Answer 3

I would give you a clue. Check the ZPosition like this.
if let spriteNode = sceneView.node(for: anchor),
spriteNode.name == "token",
intersects(spriteNode) && spriteNode.zPosition < 0 {....}