# A Needs-Based Augmented Reality System
## 2 Background
### Classification of Augmented Reality  
There are different types of AR systems and apps depending on the concepts and technology. The classification of these types is not unified; different research papers classify the types differently. [PERSON], [PERSON], and [PERSON] [18] describe six types of AR under two main categories: triggered and view-based augmentation. The triggered AR technologies include marker-based AR, location-based AR, dynamic augmentation, and complex augmentation. The view-based augmentation includes Indirect and non-specific digital augmentations. Table 2 describes the classification mentioned above. Other classifications divide AR into marker-based, marker-less, outlining AR, and superimposition AR. The marker-based type of AR depends on a marker that, when scanned by a camera, triggers an AR experience. The marker may be an image, a fiducial marker (Figure 2), or a physical object. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Core AR Technology** & \multicolumn{2}{c}{**Definition**} \\ \hline Tracking techniques & \begin{tabular}{c} “Methods of tracking a target object/environment via \\ cameras and sensors, and estimating viewpoint poses”. \\ “Techniques and interfaces for interacting with virtual \\ content”. \\ \end{tabular} \\ Calibration and registration & \begin{tabular}{c} “Geometric or photometric calibration methods, and method \\ to align multiple coordinate frames”. \\ \end{tabular} \\ Display techniques & \
\begin{tabular}{c} “Display hardware to present virtual content in AR, including \\ head-worn, handheld, and projected displays”. \\ \end{tabular} \\ AR applications &
\begin{tabular}{c} “AR systems in application domains such as medicine, \\ manufacturing, or military, among others”. \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Core augmented reality technologies and techniques [16]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Category** & **Type** & **Brief** & **Example** \\ \hline Triggered & Marker-Based & \begin{tabular}{c} Triggered by a marker: \\ Paper (image) \\ Physical object \\ \end{tabular} & \begin{tabular}{c} Museum displays \\ \end{tabular} \\  & Location-Based & Triggered by GPS location & \begin{tabular}{c} Monocle Restaurant information \\ Digitally trying clothes and accessories with \\ shopping apps \\ \end{tabular} \\ View-Based & \begin{tabular}{c} Complex Augmentation \\ Indirect Augmentation \\ Non-Specific digital \\ Augmentation \\ \end{tabular} & \
\begin{tabular}{c} A combination of the above \\ Intelligent augmentation of a static view \\ Augmentation of a dynamic view \\ \end{tabular} &
\begin{tabular}{c} Dynamic view with digital information from \\ the Internet \\ Taking a picture and changing the wall color \\ Augmentation in \\ mobile games \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Classification of augmented reality types [18]. Markerless AR does not require markers; it uses other triggers such as location-based AR. The projection-based AR is also markerless and works by projecting digital information on objects in the user's environment. Outlining AR uses the special abilities of cameras in recognizing objects in conditions that may be difficult to recognize for the eyes and provide guidance in the form of outlines on objects. Superimposition AR recognizes objects and superimposes virtual information on them. It includes face filters as done by Instagram and Snapchat. AR spans beyond the visual augmentations to include the natural senses of hearing, touch, taste, and smell forming the auditory, haptic, gustatory, and olfaction AR systems respectively. This variety in AR systems constitutes another classification based on the senses. Auditory AR is the second most common class after visual AR. It embeds auditory content into a user's acoustic environment. In many cases, the sound is integrated with visual AR to enhance it, while in others it is used as the main augmentation to support visually impaired individuals [19].