## 6 Results and Findings
Due to most of the AR selected studies being in a high level of TRL, these technologies already have been proven in an operational environment; however, it is important to consider that there are a lot of challenges and limitations, especially in some non-conventional sectors of AR, e.g., the commercialization of AR contact lenses, whose development still in an early stage. Figure 5 summarizes in an illustrative way the principal elements collected throughout the presented SLR. The map is divided into four main sections, which are: Operational Principle (the way the AR technology works), Technologies (divided into hardware and main software commonly used for development), Domains, and Challenges (including the markets in the world that invest most nowadays). In addition, Figure 6 shows the evolution of AR from the beginning of this technology (first documented developments) to 2023. The \"x\" axis is for the time and the \"y\" axis is for the level of immersiveness, ranked from 1 to 5 stars, with being 1 the less immersive and 5 being the most immersive (based on the type of technology and the way a user interacts with it). The name of the specific technology is indicated with its TRL index in parenthesis. Some of the shown AR technologies are discontinued today, however, they reached a TRL of 9 due to their \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**AR Technology** & **Reference** & **Commercial** & **Application** & **Scector** & **Publication Classification** & **Hardware** & **Software** & **Connectivity** & **Protocol** & **TRL** \\ \hline \multirow{4}{*}{Marker-Based AR} & \multirow{4}{*}{[12]} & \multirow{4}{*}{[11]} & \multirow{4}{*}{[12]} & Virtual Ty-On & Retail and & \multirow{4}{*}{[13]} & Smartphones/Tablets, & ARCore, ARKit, & & & \\  & & & & & Webcams, Depth & & Vlorida, Open/CV, & & & \\  & & & & & & & & & \\  & & & & & & & & & \\  & & & & & & & & & \\  & & & & & & & & & \\  & & & & & & & & & \\ \hline \multirow{4}{*}{Marker-Based AR} & \multirow{4}{*}{[11]} & \multirow{4}{*}{[12]} & \multirow{4}{*}{[13]} & The Museum of & \multirow{4}{*}{[14]} & \multirow{4}{*}{[13]} & Smartphones/Tablets, & ARCore, ARKit, & & & \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\ \hline \multirow{4}{*}{Marker-Based AR} & \multirow{4}{*}{[11]} & \multirow{4}{*}{[11]} & The Museum of & \multirow{4}{*}{[11]} & \multirow{4}{*}{[13]} & Museums & Smartphones/Tablets, & ARCore, ARKit, & & & \\  & & & & & & Camera, Accelerometer, & Studio, Swift, Kotlin, & & \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\ \hline \multirow{4}{*}{Markerless AR} & \multirow{4}{*}{[24]} & \multirow{4}{*}{[22]} & \multirow{4}{*}{[13]} & \multirow{4}{*}{[14]} & Smartphones/Tablets, & \multirow{4}{*}{[13]} & Google/Net Maps, & & & \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & & \\  & & & & & & & \\  & & & & & & & & \\  & & & & & & & \\ \hline \multirow{4}{*}{Marker-Based AR} & \multirow{4}{*}{[22]} & \multirow{4}{*}{[12]} & \multirow{4}{*}{[13]} & \multirow{4}{*}{[14]} & Smartphones, & Pokemon/Net, Kotlin, & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: AR application technological comparison. The version and/or manufacturer of each commercial application is the one presented in the corresponding reference.