In several visionOS apps, we readjust our scenes to the user's eye level (their heads). But, we have encountered issues whereby the WorldTrackingProvider returns bad/incorrect positions for the first x number of frames.
See below code which you can copy paste in any Immersive Space. Relaunch the space and observe the numberOfBadWorldInfos value is inconsistent.
a. what is the most reliable way to get the devices's position?
b. is this indeed a bug?
c. are we using worldInfo improperly?
d. as a workaround, in our apps we set to 10 the number of frames to let pass before using worldInfo, should we set our threshold differently?
import ARKit
import Combine
import OSLog
import SwiftUI
import RealityKit
import RealityKitContent
let SUBSYSTEM = Bundle.main.bundleIdentifier!
struct ImmersiveView: View {
let logger = Logger(subsystem: SUBSYSTEM, category: "ImmersiveView")
let session = ARKitSession()
let worldInfo = WorldTrackingProvider()
@State var sceneUpdateSubscription: EventSubscription? = nil
@State var deviceTransform: simd_float4x4? = nil
@State var numberOfBadWorldInfos = 0
@State var isBadWorldInfoLoged = false
var body: some View {
RealityView { content in
try? await session.run([worldInfo])
sceneUpdateSubscription = content.subscribe(to: SceneEvents.Update.self) { event in
guard let pose = worldInfo.queryDeviceAnchor(atTimestamp: CACurrentMediaTime()) else {
return
}
// `worldInfo` does not return correct values for the first few frames (exact number of frames is unknown)
// - known SO: https://stackoverflow.com/questions/78396187/how-to-determine-the-first-reliable-position-of-the-apple-vision-pro-device
deviceTransform = pose.originFromAnchorTransform
if deviceTransform!.columns.3.y < 1.6 {
numberOfBadWorldInfos += 1
logger.warning("\(#function) \(#line) deviceTransform.columns.3.y \(deviceTransform!.columns.3.y), numberOfBadWorldInfos \(numberOfBadWorldInfos)")
} else {
if !isBadWorldInfoLoged {
logger.info("\(#function) \(#line) deviceTransform.columns.3.y \(deviceTransform!.columns.3.y), numberOfBadWorldInfos \(numberOfBadWorldInfos)")
}
isBadWorldInfoLoged = true // stop logging.
}
}
}
}
}
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