I’ve been having some issues removing anchors. I can add anchors with no issue. They will be there the next time I run the scene. I can also get updates when ARKit sends them. I can remove anchors, but not all the time. The method I’m using is to call removeAnchor() on the data provider.
worldTracking.removeAnchor(forID: uuid)
// Yes, I have also tried `removeAnchor(_ worldAnchor: WorldAnchor)`
This works if there are more than one anchor in a scene. When I’m down to one remaining anchor, I can remove it. It seems to succeed (does not raise an error) but the next time I run the scene the removed anchor is back. This only happens when there is only one remaining anchor.
do {
// This always run, but it doesn't seem to "save" the removal when there is only one anchor left.
try await worldTracking.removeAnchor(forID: uuid)
} catch {
// I have never seen this block fire!
print("Failed to remove world anchor \(uuid) with error: \(error).")
}
I posted a video on my website if you want to see it happening.
https://stepinto.vision/labs/lab-051-issues-with-world-tracking/
Here is the full code. Can you see if I’m doing something wrong? Is this a bug?
struct Lab051: View {
@State var session = ARKitSession()
@State var worldTracking = WorldTrackingProvider()
@State var worldAnchorEntities: [UUID: Entity] = [:]
@State var placement = Entity()
@State var subject : ModelEntity = {
let subject = ModelEntity(
mesh: .generateSphere(radius: 0.06),
materials: [SimpleMaterial(color: .stepRed, isMetallic: false)])
subject.setPosition([0, 0, 0], relativeTo: nil)
let collision = CollisionComponent(shapes: [.generateSphere(radius: 0.06)])
let input = InputTargetComponent()
subject.components.set([collision, input])
return subject
}()
var body: some View {
RealityView { content in
guard let scene = try? await Entity(named: "WorldTracking", in: realityKitContentBundle) else { return }
content.add(scene)
if let placementEntity = scene.findEntity(named: "PlacementPreview") {
placement = placementEntity
}
} update: { content in
for (_, entity) in worldAnchorEntities {
if !content.entities.contains(entity) {
content.add(entity)
}
}
}
.modifier(DragGestureImproved())
.gesture(tapGesture)
.task {
try! await setupAndRunWorldTracking()
}
}
var tapGesture: some Gesture {
TapGesture()
.targetedToAnyEntity()
.onEnded { value in
if value.entity.name == "PlacementPreview" {
// If we tapped the placement preview cube, create an anchor
Task {
let anchor = WorldAnchor(originFromAnchorTransform: value.entity.transformMatrix(relativeTo: nil))
try await worldTracking.addAnchor(anchor)
}
} else {
Task {
// Get the UUID we stored on the entity
let uuid = UUID(uuidString: value.entity.name) ?? UUID()
do {
try await worldTracking.removeAnchor(forID: uuid)
} catch {
print("Failed to remove world anchor \(uuid) with error: \(error).")
}
}
}
}
}
func setupAndRunWorldTracking() async throws {
if WorldTrackingProvider.isSupported {
do {
try await session.run([worldTracking])
for await update in worldTracking.anchorUpdates {
switch update.event {
case .added:
let subjectClone = subject.clone(recursive: true)
subjectClone.isEnabled = true
subjectClone.name = update.anchor.id.uuidString
subjectClone.transform = Transform(matrix: update.anchor.originFromAnchorTransform)
worldAnchorEntities[update.anchor.id] = subjectClone
print("🟢 Anchor added \(update.anchor.id)")
case .updated:
guard let entity = worldAnchorEntities[update.anchor.id] else {
print("No entity found to update for anchor \(update.anchor.id)")
return
}
entity.transform = Transform(matrix: update.anchor.originFromAnchorTransform)
print("🔵 Anchor updated \(update.anchor.id)")
case .removed:
worldAnchorEntities[update.anchor.id]?.removeFromParent()
worldAnchorEntities.removeValue(forKey: update.anchor.id)
print("🔴 Anchor removed \(update.anchor.id)")
if let remainingAnchors = await worldTracking.allAnchors {
print("Remaining Anchors: \(remainingAnchors.count)")
}
}
}
} catch {
print("ARKit session error \(error)")
}
}
}
}
