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Cloud Anchors overview for Unreal Engine

Use Cloud Anchors to create multiplayer or collaborative AR experiences that Android and iOS users can share.

What is a Cloud Anchor?

Using Cloud Anchors, your app lets users add virtual objects to an AR scene. Multiple users can then view and interact with these objects simultaneously from different positions in a shared physical space.

Cloud Anchors are similar in behavior and function to anchors, but differ in that they're hosted on the ARCore Cloud Anchor service. This hosting enables users to share experiences.

How do Cloud Anchors work?

To enable these shared experiences, ARCore connects to the ARCore Cloud Anchor service to host and resolve anchors. This requires a working Internet connection.

Hosting and resolving involves these steps at a high level:

  1. The user creates a local anchor in their environment.

  2. During hosting, ARCore uploads data for the anchor to the ARCore Cloud Anchor service, which returns a unique ID for that anchor.

  3. The app distributes the unique ID to other users.

  4. During resolving, users with the unique ID can recreate the same anchor using the ARCore Cloud Anchor service.

To create a good user experience with Cloud Anchors, it's important to understand the hosting process in detail, so that you can accommodate your app's design to help users be successful.

Establishing and hosting an anchor

To establish and host an anchor, ARCore uses a 3D feature map of the space surrounding the anchor (the center of interest). To obtain this feature map, the device's rear camera must map the environment in and around the center of interest from different viewing angles and positions in the 30 seconds before the host call (ArSession_hostAndAcquireNewCloudAnchor()).

Beginning in ARCore SDK 1.12.0, this host call causes ARCore to upload select visual data from the last 30 seconds from the device's camera to the ARCore Cloud Anchor service, which processes the visual data to construct the 3D feature map and return a Cloud Anchor ID.

The proper creation of the 3D feature map is critical to a great user experience. Otherwise, the mapping quality may be limited, making resolving harder. To improve map quality, we recommend that user interfaces explicitly instruct users to map as much of the environment around the center of interest as possible, by moving the device around the local anchor from different viewing angles and positions.

To host a Cloud Anchor:

  1. Wait a few seconds after the session starts to give tracking time to stabilize before attempting to host an anchor.

  2. When selecting a location to host the anchor, try to find an area with visual features that are easily distinguishable from each other -- for example, a corner with visually distinct features.

  3. Point the rear device camera at the center of interest, that is, the area surrounding the point where you want to place the anchor.

  4. While keeping the camera trained on the center of interest, and while roughly maintaining the physical distance between the device and the center of interest, move the device around to map the environment from different viewing angles and positions for up to 30 seconds. Walking around in the space while keeping the device camera trained on the center of interest will enable capturing visual features of the area of interest from all angles, making resolving more robust.

  5. Call ArSession_hostAndAcquireNewCloudAnchor() to initiate the hosting request.

  6. ARCore uploads visual data, device poses, and the anchor pose via the ARCore Cloud Anchors API.

  7. The ARCore Cloud Anchor service creates a 3D feature map of the space, and returns a unique Cloud Anchor ID for the anchor to the device.

  8. Use ArSession_hostAndAcquireNewCloudAnchor to check the status of a hosted anchor (including error handling messages).

The ARCore Cloud Anchor service creates a 3D feature map of the space, and returns a unique Cloud Anchor ID to the device.

The anchor should be hosted.

ArSession_hostAndAcquireNewCloudAnchor lets you check the status of a hosted anchor (including error handling messages).

Resolving a previously hosted anchor

When another user in the same environment points their device camera at the area where the Cloud Anchor was hosted, a resolve request (ArSession_resolveAndAcquireNewCloudAnchor()) causes the ARCore Cloud Anchor service to periodically compare visual features from the scene against the 3D feature map that was created, which ARCore uses to pinpoint the user's position and orientation relative to the Cloud Anchor. This is why it is important to use the 30 seconds preceding the hosting request to map as much of the environment around the center of interest as possible.

You can initiate resolves for multiple Cloud Anchors in sequence. Up to 20 Cloud Anchors can be resolved simultaneously.

Using the same or different device than the hosting device, follow these steps to resolve the hosted anchor.

  1. Wait a few seconds after the session starts to give tracking time to stabilize before attempting to resolve an anchor.

  2. In the same environment as the hosted anchor, scan the original area of interest, ensuring that:

    • The device camera has a clear line of sight to mapped area

    • The device camera is a similar distance from the hosted anchor as the device that originally hosted the anchor.

  3. Call ArSession_resolveAndAcquireNewCloudAnchor() and use ArSession_hostAndAcquireNewCloudAnchor to periodically check the status of the resolve request.

    If you want to cancel your request, call ArAnchor_detach.

  4. ARCore continuously polls the ARCore Cloud Anchors API, sending visual data to the ARCore Cloud Anchor service.

  5. The ARCore Cloud Anchor service compares visual features from the scene against the 3D feature map that was created. When it finds a match, the service returns the pose of the Cloud Anchor.

The Cloud Anchor should resolve.

ArSession_hostAndAcquireNewCloudAnchor lets you check the status of a hosted anchor (including error handling messages). When you are done with the Cloud Anchor, call ArAnchor_detach.

Cloud Anchor privacy requirements

To comply with our updated privacy requirements for using ARCore SDKs 1.12.0 or later, you must disclose the use of Cloud Anchors prominently. For details, refer to User privacy requirements.

Data storage and access limitations

Cloud Anchors have the following data storage and access limitations:

  • In ARCore 1.20 and later, Cloud Anchors can be resolved for 365 days after they are hosted. (In versions of ARCore earlier than 1.20, Cloud Anchors could be resolved only for 24 hours after they were hosted.) You can extend the lifetime of the anchor after it is already hosted using the Cloud Anchor Management API.

  • Visual data uploaded to the cloud when hosting an anchor is discarded within twenty-four hours.

  • Anchors are resolved on the server against the 3D feature map.

  • Previously uploaded visual data is never sent to a user's device.

Best practices for a good user experience

The following best practices help create a good Cloud Anchors user experience.

  • Remember that initiating the host call uses the preceding 30 seconds of mapping to create the 3D feature map. Make sure that your app's user interface takes this into account.

  • Consider creating actions or features that are fun or could be of use to users (or both) when users are moving around the center of interest, and that that also accomplishes the task of creating a proper 3D feature map.

  • Avoid hosting or resolving Cloud Anchors on certain kinds of surfaces.

    • For best results, users should avoid reflective surfaces or surfaces without visual features, such as a blank, smooth, white wall.

  • Make sure that the lighting in the room is sufficient.

Deprecation policy

Apps built with ARCore SDK 1.12.0 or higher are covered by the Cloud Anchors API deprecation policy.

Apps built with ARCore SDK 1.11.0 or lower will be unable to host or resolve Cloud Anchors beginning December 2020 due to the SDK's use of an older, deprecated ARCore Cloud Anchor service.

Get started

To start using Cloud Anchors, see the Cloud Anchors Quickstart.

If you are new to working with anchors, see Working with anchors for an introduction.