HOW do Unity World Anchors work on the HoloLens?

Question

I'm currently building a HoloLens application and have a feature in-mind that requires holograms to be dynamically created, placed, and to persist between sessions. Those holograms don't need to be shared between devices.

I've had a nightmare trying to find (working) implementations and documentation for Unity WorldAnchors, with Azure Spatial Anchors seeming to stomp out most traces of it. Thankfully I've gotten past that and have managed to implement WorldAnchors by using the older HoloToolkit, since documentation for WorldAnchors in the newer MRTK also seems to have also disappeared.

MY QUESTION (because I am unable to find any docs for it) is how do WorldAnchors work?

• I'd hazard a guess that it's based on spatial mapping, which presents the limitation that if you have 2 identical rooms or objects that move in the original room, the anchor/s is/are going to be lost.

• What I'd LIKE to hear is that it's some magical management of transforms, which means my app has an understanding of its change in real-world location between uses even if the app is launched from a different location each time.

Does anybody know the answer or where I might look (beyond the limited Unity and MS Docs for this matter) to find out implementation details?

Thank you.

Answer 1

I'd hazard a guess that it's based on spatial mapping, which presents the limitation that if you have 2 identical rooms or objects that move in the original room, the anchor/s is/are going to be lost.

We won’t divulge the internal implementation details of the internal coding of the World Anchor but we can state that it is not based on GPS currently with HoloLens v1 or HoloLens v2. Currently, the World Anchor uses the data in the spatial map for placement. The underlying piece that is key is the anchors rely on the spatial scanning and the scanning can use wifi to improve the speed and accuracy, see these two references: 1 & 2

What I'd LIKE to hear is that it's some magical management of transforms, which means my app has an understanding of its change in real-world location between uses even if the app is launched from a different location each time.

It is certainly possible to have two identical rooms with exact layout to trick the mapping to think it is the same room. We document that here: https://docs.microsoft.com/en-us/windows/mixed-reality/coordinate-systems#headset-tracks-incorrectly-due-to-identical-spaces-in-an-environment