Patent Description:
Augmented-Reality (AR) is a modification of a virtual environment. For example, in Virtual Reality (VR), a user is completely immersed in a virtual world, whereas in AR, the user is immersed in a world where virtual objects are combined or superimposed on the real world. An AR system aims to generate and present virtual objects that interact realistically with a real-world environment and with each other. Examples of AR applications can include single or multiple player video games, instant messaging systems, and the like.

<CIT> describes systems and methods for receiving device tracking data of a first HMD device in a first coordinate system and skeleton tracking data produced by the first HMD device; receiving device tracking data from a second HMD device in a second coordinate system; receiving captured image data from the second HMD device; producing second skeleton tracking data from the captured image data representing candidate users and transforming the produced second skeleton tracking data to the second coordinate system; comparing the produced second skeleton tracking data to the device tracking data to identify the user of the first HMD device; using the skeleton tracking data produced from the captured image data to determine a location of the identified user in a second coordinate system; and based on the device tracking data and the location of the identified user, determining a transformation between the first and second coordinate systems.

<NPL>" describes an approach to spatially register multiple slam devices together without sharing maps or involving external tracking infrastructures. SynchronizAR employs a distance based indirect registration which resolves the transformations between the separate slam coordinate systems.

Further aspects of the invention are the subject of the dependent claims.

According to an aspect of the present disclosure, there is described a method comprising: receiving, by a second device, a request to join an augmented reality, AR, session initialized by a first device; in response to receiving the request, detecting a body corresponding to a user of the first device in one or more images captured by a camera of the second device; identifying a body part of the detected body corresponding to the user of the first device; determining, by the second device, a transformation in the AR session between the first device and the second device using the identified body part; and causing the AR session to be displayed by the second device based on the determined transformation.

Among other things, embodiments of the present disclosure improve the functionality of an AR creation software and system by establishing a common coordinate system for a shared AR session that is based on skeletal positions and tracking. In one embodiment, the system hosts a shared AR session that is a session in which a plurality of users via client devices can participate. Each user in the shared AR session can see the same AR objects positioned in the real-world scene from each user's own perspective. The shared AR session can be, for example, an AR, car racing game in which each user is controlling a different cat-, Each of the users are looking at the same shared AR scene that includes real-world objects being displayed on the client devices at the same time. A common AR object or set of AR objects, such as AR cars, are displayed on each of the client devices in the shared AR scene. This way, the users can view the AR scene from different orientations, positioning and perspectives while still seeing the common AR object or set of AR objects. The experience can be synchronized and shared between all the users. In this example, the actions of one user in the shared AR session can be synchronized and broadcast to all the other users. Accordingly, the shared AR session is a shared virtual space but in AR As another example, two users can point their devices towards a real-world scene containing a table. The two users can be next to each other or across the table from each other. An AR object, such as a virtual paper can be placed on the real-world table and viewed by each of the users on their respective devices. As one user modifies the virtual paper by writing in virtual ink on the paper, the other user can see the virtual paper being modified at the same time.

One challenge of generating the shared AR session is to establish the origin of the shared AR scene and how shared AR scene is aligned relative to the surroundings. For example, while the users are tracking the shared AR scene, each of the client devices can detect its location in space and its movement within the shared AR scene. However, the client devices may not detect or determine the same location of origin or how the AR scene is aligned relative to the surroundings of the respective device in the shared AR scene. Therefore, while each of the client devices are rendering the same virtual content (e.g., cars, racetrack), the virtual content may not appear at the same place within the shared AR scene on each device. For example, the virtual content may not be rotated to align in the same way on each of the client devices' display screens.

The shared AR scene can be synchronized, in some cases, using predefined markers. For example, one device can display a barcode or other suitable predefined image for another device to scan and determine the appropriate transformation for the AR scene. Namely, the orientation of a first device on which the marker is displayed when the marker is scanned by a second device can be used by the second device to determine information about the coordinate system of the first device. An example of such a system is described in further detail in commonly-owned, commonly-assigned <CIT>. While such a system generally works well for synchronizing the AR scene, generating the markers introduces some inefficiencies as images of the markers need to be stored and agreed upon before engaging in the shared AR session.

In one embodiment, the system implements a method for aligning all client devices in a shared AR session to a center of origin of the shared AR scene (or world) and rotating the shared AR scene in a particular orientation. In one embodiment, the system creates a shared AR session using skeletal tracking to establish the center of origin of the shared AR scene. Particularly, the disclosed embodiments improve upon systems that create shared AR sessions using markers by avoiding the need to predefine and store such markers. This reduces the number of steps needed to create a shared AR session, reduces overall processing and storage resources, and thereby improves the overall functioning of the electronic device. Also, by using skeletal tracking, errors in the AR session caused by drift of the common coordinate system can be corrected during the AR session. Particularly, the errors can be corrected, continuously or periodically, whenever a body is detected in the scene and without having to re-scan markers presented by other devices.

<FIG> is a block diagram showing an example system <NUM> for exchanging data (e.g., messages and associated content) over a network. The system <NUM> includes multiple instances of a client device <NUM>, each of which hosts a number of applications including a messaging client application <NUM> and an AR session client controller <NUM>. Each messaging client application <NUM> is communicatively coupled to other instances of the messaging client application <NUM> and a messaging server system <NUM> via a network <NUM> (e.g., the Internet). Each AR session client controller <NUM> is communicatively coupled to other instances of the AR session client controller <NUM> and an AR session server controller <NUM> in the messaging server system <NUM> via the network <NUM>.

A messaging client application <NUM> is able to communicate and exchange data with another messaging client application <NUM> and with the messaging server system <NUM> via the network <NUM>. The data exchanged between messaging client application <NUM>, and between a messaging client application <NUM> and the messaging server system <NUM>, includes functions (e.g., commands to invoke functions) as well as payload data (e.g., text, audio, video or other multimedia data).

The messaging server system <NUM> provides server-side functionality via the network <NUM> to a particular messaging client application <NUM>. While certain functions of the system <NUM> are described herein as being performed by either a messaging client application <NUM> or by the messaging server system <NUM>, the location of certain functionality either within the messaging client application <NUM> or the messaging server system <NUM> is a design choice. For example, it may be technically preferable to initially deploy certain technology and functionality within the messaging server system <NUM>, but to later migrate this technology and functionality to the messaging client application <NUM> where a client device <NUM> has a sufficient processing capacity.

The messaging server system <NUM> supports various services and operations that are provided to the messaging client application <NUM>. Such operations include transmitting data to, receiving data from, and processing data generated by the messaging client application <NUM>. This data may include, message content, client device information, geolocation information, media annotation and overlays, message content persistence conditions, social network information, and live event information, as examples. Data exchanges within the messaging system <NUM> are invoked and controlled through functions available via user interfaces (UIs) of the messaging client application <NUM>.

The AR session client controller <NUM> is able to communicate and exchange data with another AR session client controller <NUM> and with the AR session server controller <NUM> via the network <NUM>. The data exchanged between the AR session client controller <NUM>, and between the AR session client controller <NUM> and the AR session server controller <NUM> can include a session identifier that identifies the shared AR session, a transformation between a first device and a second device (e.g., plurality of client devices <NUM> include the first and a second device) that is used to align the shared AR session to a common point of origin, a common coordinate frame, functions (e.g., commands to invoke functions) as well as other payload data (e.g., text, audio, video or other multimedia data). In some cases, the AR session client controller <NUM> computes the transformation between two devices based on a position and orientation of a body part of a body depicted in one or more images captured by one of the two devices. For example, a first device of the two devices can include a camera that is pointed towards a user of a second device of the two devices. The first device can transmit the one or more images to the AR session server controller <NUM> along with position and orientation information of the first device. As an example, the first device can transmit the origin and coordinate system or frame of the first device. The AR session server controller <NUM> can process the one or more images to identify skeletal joint positions of the body depicted in the images. The AR session server controller <NUM> can identify a wrist joint position in the skeletal joint positions.

The AR session server controller <NUM> can compute a transformation (e.g., the common coordinate frame) based on the identified body part that represents how the identified body part is positioned in the AR scene relative to a position and orientation of the first device. Namely, the transformation represents how the wrist position that corresponds to the origin of the second device appears to the first device. As an example, the second device may be held in a right hand of the user of the second device which means that the right wrist position is the point of origin according to which the second device generates AR content. By determining where this point of origin is with respect to the first device and providing this information in the form of a transformation to the second device, the second device can determine the offset by which to shift AR content the second device presents. The AR session server controller <NUM> sends the transformation to the second device so that the second device can adjust the AR coordinate system based on the transformation. In this way, the first and second devices synch up their coordinate systems and frames for displaying content in the AR session. Specifically, the AR session server controller <NUM> computes the point of origin of the second device in the coordinate system of the first device. The AR session server controller <NUM> can then determine an offset in the coordinate system of the second device based on the position of the point of origin from the perspective of the second device in the coordinate system of the second device. This offset is used to generate the transformation so that the second device generates AR content in according to a common coordinate system or frame as the first device.

Turning now specifically to the messaging server system <NUM>, an Application Program Interface (API) server <NUM> is coupled to, and provides a programmatic interface to, an application server <NUM>. The application server <NUM> is communicatively coupled to a database server <NUM>, which facilitates access to a database <NUM> in which is stored data associated with messages processed by the application server <NUM>.

The Application Program Interface (API) server <NUM> receives and transmits message data (e.g., commands and message payloads) between the client device <NUM> and the application server <NUM>. Specifically, the Application Program Interface (API) server <NUM> provides a set of interfaces (e.g., routines and protocols) that can be called or queried by the messaging client application <NUM> in order to invoke functionality of the application server <NUM>. The Application Program Interface (API) server <NUM> exposes various functions supported by the application server <NUM>, including account registration, login functionality, the sending of messages, via the application server <NUM>, from a particular messaging client application <NUM> to another messaging client application <NUM>, the sending of media files (e.g., images or video) from a messaging client application <NUM> to the messaging server application <NUM>, and for possible access by another messaging client application <NUM>, the setting of a collection of media data (e.g., story), the retrieval of a list of friends of a user of a client device <NUM>, the retrieval of such collections, the retrieval of messages and content, the adding and deletion of friends to a social graph, the location of friends within a social graph, and opening an application event (e.g., relating to the messaging client application <NUM>).

The application server <NUM> hosts a number of applications and subsystems, including a messaging server application <NUM>, an image processing system <NUM>, a social network system <NUM>, and an AR session server controller <NUM>. The messaging server application <NUM> implements a number of message processing technologies and functions, particularly related to the aggregation and other processing of content (e.g., textual and multimedia content) included in messages received from multiple instances of the messaging client application <NUM>. As will be described in further detail, the text and media content from multiple sources may be aggregated into collections of content (e.g., called stories or galleries). These collections are then made available, by the messaging server application <NUM>, to the messaging client application <NUM>. Other processor and memory intensive processing of data may also be performed server-side by the messaging server application <NUM>, in view of the hardware requirements for such processing.

The application server <NUM> also includes an image processing system <NUM> that is dedicated to performing various image processing operations, typically with respect to images or video received within the payload of a message at the messaging server application <NUM>.

The social network system <NUM> supports various social networking functions services and makes these functions and services available to the messaging server application <NUM>. To this end, the social network system <NUM> maintains and accesses an entity graph <NUM> (as shown in <FIG>) within the database <NUM>. Examples of functions and services supported by the social network system <NUM> include the identification of other users of the messaging system <NUM> with which a particular user has relationships or is "following", and also the identification of other entities and interests of a particular user.

The application server <NUM> also includes the AR session server controller <NUM> that can communicate with the AR session client controller <NUM> in the client device <NUM> to establish individual or shared AR sessions. The AR session server controller <NUM> can also be coupled to the messaging server application <NUM> to establish an electronic group communication session (e.g., group chat, instant messaging) for the client devices in a shared AR session. The electronic group communication session can be associated with a session identifier provided by the client devices <NUM> to gain access to the electronic group communication session and to the shared AR session. In one embodiment, the client devices first gain access to the electronic group communication session and then obtain the session identifier in the electronic group communication session that allows the client devices to access to the shared AR session. In some embodiments, the client devices <NUM> are able to access the shared AR session without aid or communication with the AR session server controller <NUM> in the application server <NUM>.

The application server <NUM> is communicatively coupled to a database server <NUM>, which facilitates access to a database <NUM> in which is stored data associated with messages processed by the messaging server application <NUM>.

<FIG> is block diagram illustrating further details regarding the system <NUM>, according to example embodiments. Specifically, the system <NUM> is shown to comprise the messaging client application <NUM> and the application server <NUM>, which in turn embody a number of some subsystems, namely an ephemeral timer system <NUM>, a collection management system <NUM> and an annotation system <NUM>.

The ephemeral timer system <NUM> is responsible for enforcing the temporary access to content permitted by the messaging client application <NUM> and the messaging server application <NUM>. To this end, the ephemeral timer system <NUM> incorporates a number of timers that, based on duration and display parameters associated with a message, or collection of messages (e.g., a story), selectively display and enable access to messages and associated content via the messaging client application <NUM>. Further details regarding the operation of the ephemeral timer system <NUM> are provided below.

The collection management system <NUM> is responsible for managing collections of media (e.g., collections of text, image video and audio data). In some examples, a collection of content (e.g., messages, including images, video, text and audio) may be organized into an "event gallery" or an "event story. " Such a collection may be made available for a specified time period, such as the duration of an event to which the content relates. For example, content relating to a music concert may be made available as a "story" for the duration of that music concert. The collection management system <NUM> may also be responsible for publishing an icon that provides notification of the existence of a particular collection to the user interface of the messaging client application <NUM>.

In certain embodiments, compensation may be paid to a user for inclusion of user-generated content into a collection. In such cases, the curation interface <NUM> operates to automatically make payments to such users for the use of their content.

The annotation system <NUM> provides various functions that enable a user to annotate or otherwise modify or edit media content associated with a message. For example, the annotation system <NUM> provides functions related to the generation and publishing of media overlays for messages processed by the system <NUM>. The annotation system <NUM> operatively supplies a media overlay or supplementation (e.g., an image filter) to the messaging client application <NUM> based on a geolocation of the client device <NUM>. In another example, the annotation system <NUM> operatively supplies a media overlay to the messaging client application <NUM> based on other information, such as social network information of the user of the client device <NUM>. A media overlay may include audio and visual content and visual effects. Examples of audio and visual content include pictures, texts, logos, animations, and sound effects. An example of a visual effect includes color overlaying. The audio and visual content or the visual effects can be applied to a media content item (e.g., a photo) at the client device <NUM>. For example, the media overlay may include text that can be overlaid on top of a photograph taken by the client device <NUM>. In another example, the media overlay includes an identification of a location overlay (e.g., Venice beach), a name of a live event, or a name of a merchant overlay (e.g., Beach Coffee House). In another example, the annotation system <NUM> uses the geolocation of the client device <NUM> to identify a media overlay that includes the name of a merchant at the geolocation of the client device <NUM>. The media overlay may include other indicia associated with the merchant. The media overlays may be stored in the database <NUM> and accessed through the database server <NUM>.

In one example embodiment, the annotation system <NUM> provides a user-based publication platform that enables users to select a geolocation on a map, and upload content associated with the selected geolocation. The user may also specify circumstances under which a particular media overlay should be offered to other users. The annotation system <NUM> generates a media overlay that includes the uploaded content and associates the uploaded content with the selected geolocation.

In another example embodiment, the annotation system <NUM> provides a merchant-based publication platform that enables merchants to select a particular media overlay associated with a geolocation via a bidding process. For example, the annotation system <NUM> associates the media overlay of a highest bidding merchant with a corresponding geolocation for a predefined amount of time.

<FIG> is a schematic diagram illustrating data structures <NUM> which may be stored in the database <NUM> of the messaging server system <NUM>, according to certain example embodiments. While the content of the database <NUM> is shown to comprise a number of tables, it will be appreciated that the data could be stored in other types of data structures (e.g., as an object-oriented database).

The database <NUM> includes message data stored within a message table <NUM>. The entity table <NUM> stores entity data, including an entity graph <NUM>. Entities for which records are maintained within the entity table <NUM> may include individuals, corporate entities, organizations, objects, places, events, etc. Regardless of type, any entity regarding which the messaging server system <NUM> stores data may be a recognized entity. Each entity is provided with a unique identifier, as well as an entity type identifier (not shown).

The entity graph <NUM> furthermore stores information regarding relationships and associations between entities. Such relationships may be social, professional (e.g., work at a common corporation or organization) interested-based or activity-based, merely for example.

The database <NUM> also stores annotation data, in the example form of filters, in an annotation table <NUM>. Filters for which data is stored within the annotation table <NUM> are associated with and applied to videos (for which data is stored in a video table <NUM>) and/or images (for which data is stored in an image table <NUM>). Filters, in one example, are overlays that are displayed as overlaid on an image or video during presentation to a recipient user. Filters may be of varies types, including user-selected filters from a gallery of filters presented to a sending user by the messaging client application <NUM> when the sending user is composing a message Other types of filters include geolocation filters (also known as geo-filters) which may be presented to a sending user based on geographic location. For example, geolocation filters specific to a neighborhood or special location may be presented within a user interface by the messaging client application <NUM>, based on geolocation information determined by a GPS unit of the client device <NUM>. Another type of filter is a data filter, which may be selectively presented to a sending user by the messaging client application <NUM>, based on other inputs or information gathered by the client device <NUM> during the message creation process. Example of data filters include current temperature at a specific location, a current speed at which a sending user is traveling, battery life for a client device <NUM>, or the current time.

Other annotation data that may be stored within the image table <NUM> is so-called "LENS" data. A "LENS" may be a real-time special effect and sound that may be added to an image or a video.

As mentioned above, the video table <NUM> stores video data which, in one embodiment, is associated with messages for which records are maintained within the message table <NUM><NUM>. Similarly, the image table <NUM> stores image data associated with messages for which message data is stored in the entity table <NUM>. The entity table <NUM> may associate various annotations from the annotation table <NUM> with various images and videos stored in the image table <NUM> and the video table <NUM>.

A story table <NUM> stores data regarding collections of messages and associated image, video, or audio data, which are compiled into a collection (e.g., a story or a gallery). The creation of a particular collection may be initiated by a particular user (e.g., each user for which a record is maintained in the entity table <NUM>). A user may create a "personal story" in the form of a collection of content that has been created and sent/broadcast by that user. To this end, the user interface of the messaging client application <NUM> may include an icon that is user-selectable to enable a sending user to add specific content to his or her personal story.

A collection may also constitute a "live story," which is a collection of content from multiple users that is created manually, automatically, or using a combination of manual and automatic techniques. For example, a "live story" may constitute a curated stream of user-submitted content from varies locations and events. Users whose client devices have location services enabled and are at a common location event at a particular time may, for example, be presented with an option, via a user interface of the messaging client application <NUM>, to contribute content to a particular live story. The live story may be identified to the user by the messaging client application <NUM>, based on his or her location. The end result is a "live story" told from a community perspective.

A further type of content collection is known as a "location story", which enables a user whose client device <NUM> is located within a specific geographic location (e.g., on a college or university campus) to contribute to a particular collection. In some embodiments, a contribution to a location story may require a second degree of authentication to verify that the end user belongs to a specific organization or other entity (e.g., is a student on the university campus).

The database <NUM> can also store data pertaining to individual and shared AR sessions in the AR session table <NUM>. The data in the AR session table <NUM> can include data communicated between the AR session client controller <NUM> and another AR session client controller <NUM>, and data communicated between the AR session client controller <NUM> and the AR session server controller <NUM>. Data can include data used to establish the common coordinate frame of the shared AR scene, the transformation between the devices, the session identifier, images depicting a body, skeletal joint positions, wrist joint positions, and so forth.

<FIG> is a schematic diagram illustrating a structure of a message <NUM>, according to some in some embodiments, generated by a messaging client application <NUM> for communication to a further messaging client application <NUM> or the messaging server application <NUM>. The content of a particular message <NUM> is used to populate the message table <NUM> stored within the database <NUM>, accessible by the messaging server application <NUM>. Similarly, the content of a message <NUM> is stored in memory as "in-transit" or "inflight" data of the client device <NUM> or the application server <NUM>. The message <NUM> is shown to include the following components:.

The contents (e.g., values) of the various components of message <NUM> may be pointers to locations in tables within which content data values are stored. For example, an image value in the message image payload <NUM> may be a pointer to (or address of) a location within an image table <NUM>. Similarly, values within the message video payload <NUM> may point to data stored within a video table <NUM>, values stored within the message annotations <NUM> may point to data stored in an annotation table <NUM>, values stored within the message story identifier <NUM> may point to data stored in a story table <NUM>, and values stored within the message sender identifier <NUM> and the message receiver identifier <NUM> may point to user records stored within an entity table <NUM>.

<FIG> is a flowchart of a process for an AR session based on skeletal tracking, in accordance with some example embodiments. Although the flowcharts can describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. A process is terminated when its operations are completed. A process may correspond to a method, a procedure, and the like. The steps of methods may be performed in whole or in part, may be performed in conjunction with some or all of the steps in other methods, and may be performed by any number of different systems, such as the systems described in <FIG>, <FIG> and/or <FIG>, or any portion thereof, such as a processor included in any of the systems.

At operation <NUM>, an AR session is initialized (e.g., by a first device, by a second device, and/or on a server as a result of the first device starting an AR session). For example, the AR session client controller <NUM> in the first client device (e.g., client device <NUM>) can initialize a shared AR session.

At operation <NUM>, a second device receives a request to join the AR session of the first device. In response to receiving this request, the second device activates the AR session and initializes the AR session on the second device. In one embodiment, during initialization of the shared AR session, the first device and the second device can be in active Simultaneous Localization And Mapping (SLAM) sessions that are independent of each other, and these SLAM session maps need to be aligned with one another to establish the shared AR session. In one example, the second device receives a message, via the messaging client application <NUM>, from the first device with an AR session identifier. The second device may receive a user selection (e.g., of an on-screen button or link) to join the AR session identified in the message. The second device, in response to receiving the user selection of the on-screen button, uses the AR session identifier to join a shared AR session with the first device so that the first and second devices synch up and display the same AR content relative to the real-world scene each device displays.

In some embodiments, initializing the shared AR session includes determining, by the first device, a first device transformation (e.g., known transformation TA). The first device transformation can be based on a first device current pose and a first device origin. The first device current pose can be the position and orientation of the first device with respect to the real-world on an x, y, z-axis. The first device origin is an origin of a coordinate frame tracked by the first device. In some cases, the transformation TA can represent a transformation from the first device origin to the user's hand. Similarly, initializing the shared AR session can also include determining, by the second device, a second device transformation (e.g., known transformation TB). The second device transformation can be based on a second device current pose and a second device origin. The second device current pose can be the position and orientation of the second device with respect to the real world on an x, y, z-axis. The second device origin is an origin of a coordinate frame tracked by the second device. The origin of the coordinate frame tracked by the first device can be different from the origin of the coordinate frame tracked by the second device. As such, a common transformation is computed to synch up the coordinate frames of the first and second devices so that AR content is consistently presented on the first and second devices.

At operation <NUM>, in response to receiving the request to join the AR session of the first device, a body corresponding to a user of the first device is detected in one or more images captured by a camera of the second device. For example, in response to receiving the request, the second device displays a prompt to the user instructing the user to point the camera of the second device towards the user of the first device with whom the user of the second device would like to join the AR session. The second device captures one or more images as the user of the second device points the camera towards the user of the first device. The second device detects a body (e.g., a human pose) in the one or more images. For example, the second device detects a body in the one or more images by performing image processing and employing a human body recognition and classification process (e.g., using machine learning, such as a trained neural network).

At operation <NUM>, the second device identifies a body part of the detected body corresponding to the user of the first device. For example, the second user of the second device can point the second device towards the first user of the first device such that the body of the first user is in the field of view of the camera included in the second device. The second device can then find the wrist position or wrist skeletal joint position corresponding to the hand of the first user that is holding the first device. The AR session client controller <NUM> in the second device detects the wrist skeletal joint position or transformation by analyzing one or more images within the camera's field of view. The skeletal joint transformation includes a position of the skeletal joint in 3D space and rotation information for the skeletal joint position. In one embodiment, the AR session client controller <NUM> implements a skeletal joint detection algorithm to detect the wrist skeletal joint position and transformation. Specifically, once a body is identified in the one or more images captured by the second device, the second device generates a skeletal joint representation of the body. The skeletal joint representation identifies a set of points that correspond to different skeletal joints of the body (e.g., a head joint, shoulder joints, arm joints, wrist joints, leg joints, feet joints, and so forth).

In some embodiments, the second device analyzes the body depicted in the one or more images to identify which hand (left or right) is holding the first device. The second device selects the skeletal joint of the wrist corresponding to the hand that is holding the first device. Particularly, the origin of the coordinate system of the first device is a constant point in 3D space of the device. The first device can compute a transform relative to this constant point to represent movement of the first device over time in relation to the constant origin point. In one embodiment, the transform represents the location of the hand that is holding the first device relative to the origin of the first device. As such, by identifying the wrist skeletal joint position and transformation of the hand that is holding the first device, the second device can determine the first device location in 3D space in the coordinate system of the second device. In some embodiments, the first device may be a head mounted device. In such cases, the second device analyzes the body depicted in the one or more images to identify the head on which the first device is mounted. The second device selects the skeletal joint of the head. Particularly, the transform of the first device is based on a location in 3D space of the head on which the first device is mounted relative to the origin of the first device. As such, by identifying the head skeletal joint position and transformation of the head on which the first device is mounted, the second device can determine the first device location in 3D space in the coordinate system of the second device.

At operation <NUM>, the second device determines a transformation in the AR session between the first device and the second device using the identified body part. For example, the AR session client controller <NUM> of the second device determines a transformation (TC) between origins of the first device and the second device using the wrist skeletal joint position or transformation (e.g., the skeletal joint transformation that represents the origin in the coordinate frame of the first device and includes rotation information). The transformation (TC) can be a transformation matrix that describes the transformation between the origin of the first device and the origin of the second device. Specifically, the second device computes an offset or transformation from the origin of the first device in the coordinate system of the first device to the position of that origin in the coordinate system of the second device. As an example, the first device determines a transformation based on the origin of the first device that is at a first location in 3D space in the first device coordinate system. The second device identifies the origin of the first device (e.g., the position and transformation of the skeletal wrist joint) to be at a second location in 3D space of the second device coordinate system. The second device receives the first device coordinate system or transform determined by the first device and compares the location of the second location in the 3D space of the second device coordinate system with respect to the first location in the first device coordinate system. As an example, the second device determines that the second location is offset from the first location by <NUM> degrees and <NUM> centimeters. In response, the second device computes a transform that represents this offset between the origins of the two devices and may transmit this transform to the first device. The first device then shifts all the AR content the first device displays based on the offset indicated in the transform.

In one embodiment, the second device receives the first device transformation (TA) from the first device and further uses the first device transformation (TA) to determine the transformation (TC) between an origin of the first device and an origin of the second device. In this embodiment, the transformation (TC) can be a transformation matrix that describes the transformation between the first device transformation (TA) (determined based on an origin of the first device) and the second device transformation (TB) (determined based on an origin of the second device). The AR session client controller <NUM> of the second device can also determine a second offset based on the first device transformation (TA). The second offset can be an offset of the second device current pose and the first device origin. In this embodiment, the second offset is daisy chained with offsets computed by other devices in the shared AR session to ensure that the devices in the shared AR session can align each other on the same origin of the AR shared session (e.g., shared AR world origin).

In one embodiment, the AR session client controller <NUM> of the second device determines the transformation (Tc) between origins of the first device and the second device by using a position or transformation of the wrist skeletal joint position in the one or more images, a scale of the wrist skeletal joint position or transformation in the one or more images, or a rotation of the wrist skeletal joint position or transformation in the one or more images or any combination thereof. For example, to determine the transformation (Tc), the AR session client controller <NUM> of the second device can use basic computer vision, manipulation of the image, geometry, translation, visual representations, angles, distances, and so forth.

In one embodiment, the AR session client controller <NUM> of the second device transmits the transformation (Tc) to the AR session client controller <NUM> of the first device and/or the AR session server controller <NUM>. The AR session client controller <NUM> of the second device can also transmit the transformation (Tc) in the (group) communication session, such as via the messaging client application <NUM>. In some embodiments, the AR session client controller <NUM> of the second device determines a common coordinate frame using the transformation (Tc). In some embodiment, the AR session client controller <NUM> of the first device determines the common coordinate frame using the transformation (Tc) received from the second device.

At operation <NUM>, the AR session client controller <NUM> in the first device causes the shared AR session to be displayed by the first device and the AR session client controller <NUM> in the second device causes the shared AR session to be displayed by the second device based on the determined transformation. In one embodiment, the shared AR scenes included in the shared AR session are caused to be displayed by the first device and the second device.

The AR session client controller <NUM> of the second device filters out images of the wrist joint position or transformation that result in a transformation (Tc) that is contrary to gravity. Although the frames captured of the wrist joint position or transformation are offset in rotation in a position along the ground plane, both the first device and the second device can align each other on where the ground is (e.g., which direction is up versus down). The AR session client controller <NUM> of the second device performs a gravity check by determining whether the first current pose that is observed (or the image of the wrist joint position that is captured) is contrary to gravity.

The AR session client controller <NUM> of the second device receives information including the angle of the gravity axis and uses this information to compare with the tracking data of the wrist joint position (e.g., frames captured of the marker by the camera in second device). The AR session client controller <NUM> of the second device then checks whether the first device and the second device match how the poses of the first device are oriented with respect to the gravity position. The AR session client controller <NUM> of the second device can then filter out the data (or frames captured of the marker) where there is disagreement on the orientation with respect to the gravity position (e.g., lower quality data).

As an example, after the transform is provided to the first device, the first and second device synchronize display of AR content. Specifically, the respective cameras of the first device and second device can be pointed at a real-world table from different angles. The AR session may cause an AR paper object (e.g., virtual paper) to be displayed on top of the real-world table. In such cases, the first device displays the AR, paper object on top of the real-world table on a screen of the first device at the same time as the second device displays the same common AR paper object on top of the same real-world table on a screen of the second device. To synchronize the location of the AR paper, the first device shifts or changes the position of the placement of the AR paper object relative to the origin of the first device coordinate frame based on the transformation received from the second device.

In some embodiments, the second device re-computes or re-calculates the transformation between the coordinate system of the first and second device when the body of the user of the first device is detected in one or more images captured by the second device. For example, the first and second devices begin engaging in a shared AR session using an initially computed transformation. The transformation may have been computed or determined by the second device using a marker displayed by the first device and/or by identifying a skeletal wrist joint position or transformation of the user of the first device. At some later time (e.g., after five minutes) of the first and second devices being engaged in the shared AR session, the second device may again identify a body and a corresponding body part (e.g., a wrist skeletal joint position) in the real-world images captured by the second device. In response to identifying the body, the second device performs the above described process to compute a second transformation in the AR session between the first device and the second device using the identified body part. In some embodiments, the second transformation is computed each time the body is identified in the one or more images captured by the second device. In some embodiments, the second transformation is computed periodically at predetermined time intervals (e.g., every five minutes into the shared AR session). In such cases, after the predetermined time interval elapses, then the second device starts processing images captured by the second device to identify a body of the user of the first device. In some implementations, the body of the user of the first device may not appear until a few minutes or hours after the predetermined time interval is reached. But once the body is identified a few minutes or hours after the predetermined time interval is reached, the second transformation is computed based on the body that is identified. In some cases, an image of the body of the user of the first device is captured before the predetermined time interval is reached but is buffered and processed after the predetermined time interval is reached to compute the second transformation.

In some embodiments, the second device compares the second transformation that has been most recently computed with a previously computed and determined transformation. The second device computes an error based on comparing the second transformation with the previously computed and determined transformation. The second device determines whether or not to update the transformation used by the first device with the second transformation based on the value of the error with respect to a threshold. Specifically, if the second device determines that the error is less than a threshold, the second device prevents updating the transformation used by the first device with the second transformation. Namely, the first device maintains presenting the shared AR session content based on the previously determined transformation and not based on the most recently computed second transformation.

In some implementations, if the second device determines that the error is equal to or greater than the threshold, the second device causes the AR session to be displayed based on the second transformation. Specifically, the second device sends the second transformation to the first device with an instruction to replace the currently used transformation with the second transformation. An reference above or below to skeletal joint positions should be understood to include the position in 3D space of the skeletal joint position as well as rotational information about the skeletal joint position.

In some embodiments, a plurality of thresholds are stored or accessed by the second device. The threshold against which the second device compares the error between two transformations is selected from the plurality of thresholds based on positioning of content within the shared AR session. As an example, a first threshold of the plurality of thresholds may correspond to AR content that is positioned in relation to one or more real-world objects. Specifically, the first threshold may correspond to the display of virtual objects on top of, underneath, on the side of, or at some other position relative to a real-world object. For instance, the first threshold may correspond to a virtual paper object placed on top of a table. Such a threshold may be a very small value as the precision in placement of the virtual object may need to be high. In such cases, the first and second devices may need to very accurately place the virtual object relative to the real-world object. As another example, a second threshold that is larger than the first threshold may correspond to AR content that is positioned independently of any real-world objects. Specifically, the second threshold may correspond to display of a virtual object anywhere in the real-world scene, such as a floating virtual paper or virtual graphics. The positioning of such a virtual object does not depend on the positioning of the real-world object and, as such, the level of precision in placement of the virtual object may be kept low. As another example, a third threshold may correspond to the type of virtual content that is presented in an AR session. Specifically, the third threshold may be a relatively large value when the virtual content corresponds to a first object size and may be a relatively small value when the virtual content corresponds to a second object size that is smaller than the first object size. The third threshold may be a relatively large value when the virtual content corresponds to a static object and may be a relatively small value when the virtual content corresponds to an animated object.

In some embodiments, the second device determines what type of virtual content is being displayed in the shared AR session between the first and second devices and whether the virtual content is placed in relation to real-world objects. The second device selects one of the plurality of thresholds to compare against the error between the transformations based on the type of virtual content and whether the virtual content is positioned or placed in relation to real-world objects or not. In some cases, multiple AR objects are displayed in a shared AR session. In such cases, the second device retrieves multiple thresholds corresponding to each of the AR objects and selects the threshold having the smallest value of the multiple thresholds. The selected threshold is used by the second device to compare against the error computed between the second transformation and a previously computed transformation currently being used to generate the shared AR session.

In some embodiments, the second device can join a shared AR session with the first device by adjusting a transformation determined by the second device. In such cases, each device that joins the AR session may not need to transmit back a shared transformation. For example, the second device can identify the skeletal joint position corresponding to the first device (e.g., the hand that is holding the first device or the head on which the first device is mounted). The second device can compute a transformation of the coordinate frame the second device determines based on an origin of the second device based on a point in 3D space corresponding to the identified skeletal joint position. The second device can adjust the coordinate frame of the second device based on the transformation. This way, placement and positioning of virtual content presented by the second device is adjusted relative to the origin of the second device and the identified skeletal joint position corresponding to the first device. The virtual content placement and positioning is synchronized with the manner at which the same content is presented on the first device based on the transformation computed by the second device. In this implementation, the device that is joining the shared AR session (e.g., the second device) adjusts its own coordinate frame used to present AR content rather than the device that initiated the AR session (e.g., the first device). The first device in this case continues to present content in the AR session based on the coordinate frame of the first device without adjusting the coordinate frame based on the computed transformation. The second device adjusts the coordinate frame of the second device based on the computed transformation to synchronize display of the content on the second device based on the determined position in 3D space of the first device using the skeletal joint position corresponding to the first device.

The operating system <NUM> manages hardware resources and provides common services. The operating system <NUM> includes, for example, a kernel <NUM>, services <NUM>, and drivers <NUM>. The kernel <NUM> acts as an abstraction layer between the hardware and the other software layers. For example, the kernel <NUM> provides memory management, processor management (e.g., scheduling), component management, networking, and security settings, among other functionality. The services <NUM> can provide other common services for the other software layers. The drivers <NUM> are responsible for controlling or interfacing with the underlying hardware. For instance, the drivers <NUM> can include display drivers, camera drivers, BLUETOOTH® or BLUETOOTH® Low Energy drivers, flash memory drivers, serial communication drivers (e.g., Universal Serial Bus (USB) drivers), WI-FI® drivers, audio drivers, power management drivers, and so forth.

The libraries <NUM> provide a low-level common infrastructure used by the applications <NUM>. The libraries <NUM> can include system libraries <NUM> (e.g., C standard library) that provide functions such as memory allocation functions, string manipulation functions, mathematic functions, and the like. In addition, the libraries <NUM> can include API libraries <NUM> such as media libraries (e.g., libraries to support presentation and manipulation of various media formats such as Moving Picture Experts Group-<NUM> (MPEG4), Advanced Video Coding (H. <NUM> or AVC), Moving Picture Experts Group Layer-<NUM> (MP3), Advanced Audio Coding (AAC), Adaptive Multi-Rate (AMR) audio codec, Joint Photographic Experts Group (JPEG or JPG), or Portable Network Graphics (PNG)), graphics libraries (e.g., an OpenGL framework used to render in two dimensions (2D) and three dimensions (3D) in a graphic content on a display), database libraries (e.g., SQLite to provide various relational database functions), web libraries (e.g., WebKit to provide web browsing functionality), and the like. The libraries <NUM> can also include a wide variety of other libraries <NUM> to provide many other APIs to the applications <NUM>.

The frameworks <NUM> provide a high-level common infrastructure that is used by the applications <NUM>. For example, the frameworks <NUM> provide various graphical user interface (GUI) functions, high-level resource management, and high-level location services. The frameworks <NUM> can provide a broad spectrum of other APIs that can be used by the applications <NUM>, some of which may be specific to a particular operating system or platform.

In an example embodiment, the applications <NUM> may include a home application <NUM>, a contacts application <NUM>, a browser application <NUM>, a book reader application <NUM>, a location application <NUM>, a media application <NUM>, a messaging application <NUM>, a game application <NUM>, and a broad assortment of other applications such as third-party applications <NUM>. The applications <NUM> are programs that execute functions defined in the programs. Various programming languages can be employed to create one or more of the applications <NUM>, structured in a variety of manners, such as object-oriented programming languages (e.g., Objective-C, Java, or C++) or procedural programming languages (e.g., C or assembly language). In a specific example, the third-party applications <NUM> (e.g., applications developed using the ANDROID™ or IOS™ software development kit (SDK) by an entity other than the vendor of the particular platform) may be mobile software running on a mobile operating system such as IOS™, ANDROID™, WINDOWS® Phone, or another mobile operating system. In this example, the third-party applications <NUM> can invoke the API calls <NUM> provided by the operating system <NUM> to facilitate functionality described herein.

<FIG> is a diagrammatic representation of a machine <NUM> within which instructions <NUM> (e.g., software, a program, an application, an applet, an app, or other executable code) for causing the machine <NUM> to perform any one or more of the methodologies discussed herein may be executed. For example, the instructions <NUM> may cause the machine <NUM> to execute any one or more of the methods described herein. The instructions <NUM> transform the general, non-programmed machine <NUM> into a particular machine <NUM> programmed to carry out the described and illustrated functions in the manner described. The machine <NUM> may operate as a standalone device or may be coupled (e.g., networked) to other machines. In a networked deployment, the machine <NUM> may operate in the capacity of a server machine or a client machine in a server-client network environment, or as a peer machine in a peer-to-peer (or distributed) network environment The machine <NUM> may comprise, but not be limited to, a server computer, a client computer, a personal computer (PC), a tablet computer, a laptop computer, a netbook, a set-top box (STB), a PDA, an entertainment media system, a cellular telephone, a smart phone, a mobile device, a wearable device (e.g., a smart watch), a smart home device (e.g., a smart appliance), other smart devices, a web appliance, a network router, a network switch, a network bridge, or any machine capable of executing the instructions <NUM>, sequentially or otherwise, that specify actions to be taken by the machine <NUM>. Further, while only a single machine <NUM> is illustrated, the term "machine" shall also be taken to include a collection of machines that individually or jointly execute the instructions <NUM> to perform any one or more of the methodologies discussed herein.

The machine <NUM> may include processors <NUM>, memory <NUM>, and I/O components <NUM>, which may be configured to communicate with each other via a bus <NUM>. In an example embodiment, the processors <NUM> (e.g., a Central Processing Unit (CPU), a Reduced Instruction Set Computing (RISC) processor, a Complex Instruction Set Computing (CISC) processor, a Graphics Processing Unit (GPU), a Digital Signal Processor (DSP), an ASIC, a Radio-Frequency Integrated Circuit (RFIC), another processor, or any suitable combination thereof) may include, for example, a processor <NUM> and a processor <NUM> that execute the instructions <NUM>. The term "processor" is intended to include multi-core processors that may comprise two or more independent processors (sometimes referred to as "cores") that may execute instructions contemporaneously. Although <FIG> shows multiple processors <NUM>, the machine <NUM> may include a single processor with a single core, a single processor with multiple cores (e.g., a multi-core processor), multiple processors with a single core, multiple processors with multiples cores, or any combination thereof.

The instructions <NUM> may also reside, completely or partially, within the main memory <NUM>, within the static memory <NUM>, within machine-readable medium <NUM> within the storage unit <NUM>, within at least one of the processors <NUM> (e.g., within the processor's caclue memory), or any suitable combination thereof, during execution thereof by the machine <NUM>.

The I/O components <NUM> may include a wide variety of components to receive input, provide output, produce output, transmit information, exchange information, capture measurements, and so on. The specific I/O components <NUM> that are included in a particular machine will depend on the type of machine. For example, portable machines such as mobile phones may include a touch input device or other such input mechanisms, while a headless server machine will likely not include such a touch input device. It will be appreciated that the I/O components <NUM> may include many other components that are not shown in <FIG>. In various example embodiments, the I/O components <NUM> may include output components <NUM> and input components <NUM>. The output components <NUM> may include visual components (e.g., a display such as a plasma display panel (PDP), a light emitting diode (LED) display, a liquid crystal display (LCD), a projector, or a cathode ray tube (CRT)), acoustic components (e.g., speakers), haptic components (e.g., a vibratory motor, resistance mechanisms), other signal generators, and so forth. The input components <NUM> may include alphanumeric input components (e.g., a keyboard, a touch screen configured to receive alphanumeric input, a photo-optical keyboard, or other alphanumeric input components), point-based input components (e.g., a mouse, a touchpad, a trackball, a joystick, a motion sensor, or another pointing instrument), tactile input components (e.g., a physical button, a touch screen that provides location and/or force of touches or touch gestures, or other tactile input components), audio input components (e.g., a microphone), and the like.

In further example embodiments, the I/O components <NUM> may include biometric components <NUM>, motion components <NUM>, environmental components <NUM>, or position components <NUM>, among a wide array of other components. For example, the biometric components <NUM> include components to detect expressions (e.g., hand expressions, facial expressions, vocal expressions, body gestures, or eye tracking), measure biosignals (e.g., blood pressure, heart rate, body temperature, perspiration, or brain waves), identify a person (e.g., voice identification, retinal identification, facial identification, fingerprint identification, or electroencephalogram-based identification), and the like. The motion components <NUM> include acceleration sensor components (e.g., accelerometer), gravitation sensor components, rotation sensor components (e.g., gyroscope), and so forth. The environmental components <NUM> include, for example, illumination sensor components (e.g., photometer), temperature sensor components (e.g., one or more thermometers that detect ambient temperature), humidity sensor components, pressure sensor components (e.g., barometer), acoustic sensor components (e.g., one or more microphones that detect background noise), proximity sensor components (e.g., infrared sensors that detect nearby objects), gas sensors (e.g., gas detection sensors to detection concentrations of hazardous gases for safety or to measure pollutants in the atmosphere), or other components that may provide indications, measurements, or signals corresponding to a surrounding physical environment. The position components <NUM> include location sensor components (e.g., a GPS receiver component), altitude sensor components (e.g., altimeters or barometers that detect air pressure from which altitude may be derived), orientation sensor components (e.g., magnetometers), and the like.

Communication may be implemented using a wide variety of technologies. The I/O components <NUM> further include communication components <NUM> operable to couple the machine <NUM> to a network <NUM> or devices <NUM> via a coupling <NUM> and a coupling <NUM>, respectively. For example, the communication components <NUM> may include a network interface component or another suitable device to interface with the network <NUM>. In further examples, the communication components <NUM> may include wired communication components, wireless communication components, cellular communication components, Near Field Communication (NFC) components, Bluetooth® components (e.g., Bluetooth® Low Energy), Wi-Fi® components, and other communication components to provide communication via other modalities. The devices <NUM> may be another machine or any of a wide variety of peripheral devices (e.g., a peripheral device coupled via a USB).

The various memories (e.g., memory <NUM>, main memory <NUM>, static memory <NUM>, and/or memory of the processors <NUM>) and/or storage unit <NUM> may store one or more sets of instructions and data structures (e.g., software) embodying or used by any one or more of the methodologies or functions described herein. These instructions (e.g., the instructions <NUM>), when executed by processors <NUM>, cause various operations to implement the disclosed embodiments.

The instructions <NUM> may be transmitted or received over the network <NUM>, using a transmission medium, via a network interface device (e.g., a network interface component included in the communication components <NUM>) and using any one of a number of well-known transfer protocols (e.g., hypertext transfer protocol (HTTP)). Similarly, the instructions <NUM> may be transmitted or received using a transmission medium via the coupling <NUM> (e.g., a peer-to-peer coupling) to the devices <NUM>.

Turning now to <FIG>, there is shown a diagrammatic representation of a processing environment <NUM>, which includes the processor <NUM>, the processor <NUM>, and a processor <NUM> (e.g., a GPU, CPU or combination thereof).

The processor <NUM> is shown to be coupled to a power source <NUM>, and to include (either permanently configured or temporarily instantiated) modules, namely an AR session client controller component <NUM>. The AR session client component <NUM> operationally can, for example, initialize a shared AR session, cause a marker to be displayed, capture an image of the marker using a camera, generate a transformation (TC) and a common coordinate frame, and causes the shared AR session to be displayed. While not shown the processor <NUM> can alternatively include an AR session server controller component that can perform the operations of the AR. session server controller <NUM>. As illustrated, the processor <NUM> is communicatively coupled to both the processor <NUM> and processor <NUM>.

Where a phrase similar to "at least one of A, B, or C," "at least one of A, B, and C," "one or more A, B, or C," or "one or more of A, B, and C" is used, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B and C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and <NUM> and C.

Claim 1:
A method comprising:
receiving (<NUM>), by a second device, a request to join an augmented reality, AR, session initialized by a first device;
in response to receiving the request, detecting (<NUM>) a body corresponding to a user of the first device in one or more images captured by a camera of the second device;
identifying (<NUM>) a body part of the detected body, the body part including a hand that is holding the first device and a wrist corresponding to the hand;
determining (<NUM>), by the second device, a transformation in the AR session between the first device and the second device using the identified body part; and
causing the AR session to be displayed by the second device based on the determined transformation;
the method further comprising:
receiving, at the second device, information including an angle of a gravity axis for the one or more images;
comparing, at the second device, the angle of the gravity axis to tracking data of a wrist joint position of the wrist; and
based on the comparing, filtering out, at the second device, images of the wrist joint position or the determined transformation where there is a disagreement on an orientation of the first device with respect to the gravity axis.