Cloud Anchors developer guide for Android NDK (C)

Learn how to use Cloud Anchors in your own apps.

Prerequisites

Make sure that you understand fundamental AR concepts and how to configure an ARCore session before proceeding.

If you are new to Cloud Anchors, make sure that you understand how anchors and Cloud Anchors work.

Enable the ARCore API

Before using Cloud Anchors in your app, you must first enable the ARCore API in your application.

Enable Cloud Anchor capabilities in the session configuration

Once Cloud Anchors functionality has been enabled in your app, enable Cloud Anchors capabilities in your app’s AR session configuration so that it can communicate with the ARCore API:

// Create a new ARCore session.
ArSession* session = NULL;
CHECK(ArSession_create(env, context, &session) == AR_SUCCESS);

// Create a session config.
ArConfig* config = NULL;
ArConfig_create(session, &config);
ArSession_getConfig(session, config);

// Enable Cloud Anchor mode.
ArConfig_setCloudAnchorMode(session, config,
                            AR_CLOUD_ANCHOR_MODE_ENABLED);

// Configure the session.
ArSession_configure(session, config);
ArConfig_destroy(config);

Host a Cloud Anchor

Hosting starts with a call to ArSession_hostCloudAnchorAsync(). ARCore will upload visual data, device poses, and the anchor pose to the ARCore API. The API then processes this information to construct a 3D feature map, ultimately returning a unique Cloud Anchor ID for the anchor to the device.

You can also extend the lifetime of a hosted anchor using the ARCore Cloud Anchor Management API.

Your app should follow these steps to complete hosting of a Cloud Anchor:

1. Call ArSession_hostCloudAnchorAsync().
2. Wait for the callback, or continually check the Future state until it is done.
3. Check the result state to determine if the operation succeeded, or interpret the error code if it failed.
4. Share the result Cloud Anchor ID with other clients, and use it to resolve the Cloud Anchor with ArSession_resolveCloudAnchorAsync().

Check the mapping quality of feature points

ArFeatureMapQuality indicates the quality of feature points seen by ARCore in the preceding few seconds from a given camera pose. Cloud Anchors hosted using higher quality features are generally more accurately resolved. Use ArSession_estimateFeatureMapQualityForHosting() to obtain an estimation for the feature map quality for a given camera pose.

Resolve a previously hosted anchor

Call ArSession_resolveCloudAnchorAsync() to resolve a hosted Cloud Anchor. The ARCore API periodically compares visual features from the scene against the anchor’s 3D feature map to pinpoint the user's position and orientation relative to the anchor. When it finds a match, the API returns the pose of the hosted Cloud Anchor.

You can initiate resolves for multiple Cloud Anchors in sequence. Up to 40 concurrent Cloud Anchor operations can exist at a time.

Cancel an operation or remove a Cloud Anchor

Call ArFuture_cancel() to cancel a pending Cloud Anchor operation. Call ArAnchor_detach() to stop tracking and forget an already-resolved Cloud Anchor. References to the anchor must be released separately by calling ArAnchor_release().

Check the result state of a Cloud Anchor operation

Use ArCloudAnchorState to check the result status of the hosting or resolving operation, including errors.

API quotas for host and resolve requests

The ARCore API has the following quotas for request bandwidth:

Best practices for a good user experience

Instruct users to do the following to ensure a good user experience on your app:

• Wait a few seconds after the session starts before attempting to host an anchor (by placing an object, etc.). This gives the tracking some time to stabilize.
• When selecting a location to host the anchor, try to find an area with visual features that are easily distinguishable from one another. For best results, avoid reflective surfaces or surfaces that lack visual features, such as blank white walls.

• Keep the camera trained on the center of interest and move the device around the center of interest to map the environment from different angles, maintaining roughly the same physical distance as you do so. This will help capture more visual data and make resolving more robust.

• Make sure that there is sufficient lighting in the real-life environment while hosting and resolving Cloud Anchors.

Deprecation policy

• Apps built with ARCore SDK 1.12.0 or higher are covered by the Cloud Anchor API deprecation policy.
• Apps built with ARCore SDK 1.11.0 or lower are unable to host or resolve Cloud Anchors due to the SDK's use of an older, deprecated ARCore API.

What's next

• Check out the Android NDK reference documentation for more ways to use ARCore in your app.