SceneKit projectPoint incorrect after rotating SCNNode.pivot - ios

Question

I would like to retrieve the screencoordinates from a SCNNode so I can use these coordinates in a SpriteKit-overlay.
The node is a child node.
When I rotate the parent node's pivot projectPoint returns garbled results.
SCNScene:
class ScenekitScene:SCNScene {
override init() {
super.init()
let nodeCamera = SCNNode()
nodeCamera.camera = SCNCamera()
rootNode.addChildNode(nodeCamera)
let geoPyramid = SCNPyramid(width: 0.2, height: 0.5, length: 0.2)
let nodeCenterOfUniverse = SCNNode(geometry: geoPyramid)
nodeCenterOfUniverse.position = SCNVector3(0, 0, -5)
nodeCenterOfUniverse.pivot = SCNMatrix4MakeRotation(CGFloat.pi/4, 0.0, 0.0, 1.0)
rootNode.addChildNode(nodeCenterOfUniverse)
let geoSphere = SCNSphere(radius: 0.3)
let nodePlanet = SCNNode(geometry: geoSphere)
nodePlanet.name = "planet"
nodePlanet.position = SCNVector3(2, 0, 0)
nodeCenterOfUniverse.addChildNode(nodePlanet)
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
SCNSceneRenderDelegate:
extension ViewController:SCNSceneRendererDelegate {
func renderer(_ renderer: SCNSceneRenderer, didRenderScene scene: SCNScene, atTime time: TimeInterval) {
if let planet = scene.rootNode.childNode(withName: "planet", recursively: true) {
let position = planet.convertPosition(planet.position, to: scene.rootNode)
let screencoords = renderer.projectPoint(position)
print (screencoords)
# result:
# SCNVector3(x: 461.913848876953, y: 2.58612823486328, z: 0.808080852031708)
# y should clearly be more to the center of the screen somewhere between 100-200
}
}
}
Does anyone know how to get the correct screencoordinates?

Answer 1

It looks like the planet position in world coordinates is not correct.
When I manually calculate the planet position I get different results and projectPoints works as advertised. [I might post a different question regarding the worldTransform].
// using SIMD
let pivCou = float4x4(nodeCenterOfUniverse.pivot)
let posCou = float3(nodeCenterOfUniverse.position)
let posCou4 = float4(posCou.x, posCou.y, posCou.z, 1.0) // convert float3 to float4
let posPlanet = float3(nodePlanet.position)
let posPlanet4 = float4(posPlanet.x, posPlanet.y, posPlanet.z, 1.0)
let worldcoordinatesPlanet = posCou4 + posPlanet4 * pivCou