Enabling an Augmented Reality Ecosystem: A Content-oriented Survey

Motivation:

• Augmented Reality (AR) is an emerging technology that provides a user experience of augmenting the real world with virtual objects, and allows the user to interact with the virtual objects in real time and space. An AR ecosystem brings content providers, users, AR application developers, AR device manufacturers, and researchers together, making the whole AR environment sustainable. As technology (e.g., sensor tracking, ad hoc routing, computer vision and mobile computing) for supporting AR applications is developing rapidly, content is emerging as a key issue to focus on. 

Main points:

• Author introduced and explained some basic definitions of the AR. Including three characteristics of AR are identified: Combine real and virtual objects in a real environment; Run interactively in both 3D and real time; and Align real and virtual objects with each other. And then the author introduced the function and ability of each part of the AR ecosystem framework. 
• The state of art in AR from the content generation perspective is reviewed, and three key steps are introduced, namely data collection, content fusion, and content display.
• The author talked about data collection from two prospectives, through local devices or cloud servers. Local devices contains sensors(direct-field sensor, inertial sensor and GPS) and cameras. The data exchanging between an AR device and a cloud server is necessary because the local computing power and database memory are often not powerful. At last, the author gave some drawbacks of these ways of data collection.
• Then the author talked about content fusion pipeline. The author choice two main part of pipeline to extend. First is offline data preprocessing. Information integration in the database can be regarded as offline content selection or data preprocessing. The second is online fusion which information is automatically selected in real time, depending on the particular location, orientation, and user’s preference. The author gave filtering criteria and three kinds of information filtering methods including distance-based filtering, visibility-based filtering and advanced filtering. Offline data preprocessing deals with large amounts of data in cloud servers with high speed and the data is stored with a predefined structure. After that the online content selection is processed by local AR devices as real-time data is collected from devices. 
• Content display can be classified into the following categories: head-mounted, projection-based, and handheld. Head-mounted has two categories optical see-through and video see-through. 
• The last author stated some current trans and issues including tracking and registration; content fusion, energy-efficiency and cloud computing; and security and privacy issues.

Trade-offs:

• The author gave a very clear logic to state this survey. From the beginning to the end, I learned the knowledge from shallow to deep. The paper provides a survey on the state of art in AR from a content-oriented perspective. The general concept and main components of the AR ecosystem are described, and a core component of the AR ecosystem, the content component, is introduced. Three main steps are how to collect, aggregate, and display content. 
• The author basically used words and sentences to state his viewpoints. I think the paper needs more concrete examples and experiments to be convincing. Especially the data is very important. I think author should add some data and chart flows to state his viewpoints in the current AR systems and current trends and issues these two parts.