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1-introduction/related-work/2-augmented-reality.tex
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@@ -12,53 +12,20 @@ The first \AR \HMD was invented by \textcite{sutherland1968headmounted}: With th
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Fixed to the ceiling, the headset displayed a stereoscopic (one image per eye) perspective projection of the virtual content on a transparent screen, taking into account the user's position, and thus already following the interaction loop presented in \figref[introduction]{interaction-loop}.
\paragraph{A Definition of AR}
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This system also already fulfilled the first formal definition of \AR, proposed by \textcite{azuma1997survey} in the first survey of the domain: (1) \emph{combine real and virtual}, (2) \emph{be interactive in real time} and (3) \emph{register real and virtual}\footnote{This third characteristic has been slightly adapted to use the version of \textcite{marchand2016pose}, the original definition was: \enquote{registered in \ThreeD}.}.
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Each of these characteristics is essential: the real-virtual combination distinguishes \AR from \VR, a movie with integrated digital content is not interactive and a \TwoD overlay like an image filter is not registered.
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There are also two key aspects to this definition: it does not focus on technology or method, but on the user's perspective of the system experience, and it does not specify a particular human sense, \ie it can be auditory~\cite{yang2022audio}, haptic~\cite{bhatia2024augmenting}, or even olfactory~\cite{brooks2021stereosmell} or gustatory~\cite{brooks2023taste}.
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Yet, most of the research have focused on visual augmentations, and the term \AR (without a prefix) is almost always understood as visual \AR (\v-\AR).
\paragraph{On Presence}
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Despite this clear and acknowledged definition and the viewpoint of this thesis that \AR and \VR are two type of \MR experience with different levels of mixing real and virtual environments, as presented in \secref[introduction]{visuo_haptic_augmentations}, there is still a debate on defining \AR and \MR as well as how to characterize and categorized such experiences~\cite{speicher2019what,skarbez2021revisiting}.
\emph{Presence} is one of the key concept to characterize a \VR experience.
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\AR and \VR are both essentially illusions as the virtual content does not physically exist but is just digitally simulated and rendered to the user's perception through a user interface and the user's senses.
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Such experience of disbelief suspension in \VR is what is called presence, and it can be decomposed into two dimensions: \PI and \PSI~\cite{slater2009place}.
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\PI is the sense of the user of \enquote{being there} in the \VE, and it emerges from the real time rendering of the \VE from the user's perspective, the displayed content conforming and being consistent with the proprioception and actions of the user.
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\PSI is the illusion that the virtual events are really happening, even if the user knows that they are not real.
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It doesn't mean that the virtual events are realistic, but that they are plausible and coherent with the user's expectations.
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A third strong illusion in \VR is the \SoE, which is the illusion that the virtual body is one's own~\cite{slater2022separate,guy2023sense}.
The \AR presence is far less defined and studied than for \VR~\cite{tran2024survey}, but it will be useful to design, evaluate and discuss our contributions in the next chapters.
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Thereby, \textcite{slater2022separate} proposed to invert \PI as bring the virtual into the physical world, \ie \enquote{place it here}.
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As with VR, \VOs must be able to be seen from different angles by moving the head but also, this is more difficult, be consistent with the \RE, \eg occlude or be occluded by real objects~\cite{macedo2023occlusion}, cast shadows or reflect lights.
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The \PSI can be applied to \AR as is, but the \VOs must additionally have knowledge of the \RE and react accordingly to it.
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\textcite{skarbez2021revisiting} also named \PI for \AR as \enquote{immersion} and \PSI as \enquote{coherence}, and these terms will be used in the remainder of this thesis.
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Finally, as presence, \SoE in \AR is a recent topic and little is known about its perception on the user experience~\cite{genay2021virtual}.
Yet, most of the research have focused on visual augmentations, and the term \AR (without a prefix) is almost always understood as \v-\AR.
%For example, \textcite{milgram1994taxonomy} proposed a taxonomy of \MR experiences based on the degree of mixing real and virtual environments, and \textcite{skarbez2021revisiting} revisited this taxonomy to include the user's perception of the experience.
% debate on the definition of AR
% big brother VR and issue with presence/plausibility in AR (Slater)
% taxonomy of Milgram/Skarbez
\paragraph{Applications}
\subsubsection{Applications}
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Advances in technology, research and development have enabled many usages of \AR, including medicine, education, industrial, navigation, collaboration and entertainment applications~\cite{dey2018systematic}.
%
@@ -84,21 +51,44 @@ Most of \AR/\VR experience can now be implemented with commercially available ha
\subfig{roo2017inner}
\end{subfigs}
\subsubsection{How does AR work?}
% How it works briefly
\paragraph{Calibrating \& Tracking}
% \cite{marchand2016pose}
\paragraph{Modeling \& Rendering}
\paragraph{Displays}
\subsubsection{Displays}
% Bimber and types of AR
% State of current HMD
\subsubsection{On Presence and Embodiment}
Despite this clear and acknowledged definition and the viewpoint of this thesis that \AR and \VR are two type of \MR experience with different levels of mixing real and virtual environments, as presented in \secref[introduction]{visuo_haptic_augmentations}, there is still a debate on defining \AR and \MR as well as how to characterize and categorized such experiences~\cite{speicher2019what,skarbez2021revisiting}.
\emph{Presence} is one of the key concept to characterize a \VR experience.
%
\AR and \VR are both essentially illusions as the virtual content does not physically exist but is just digitally simulated and rendered to the user's perception through a user interface and the user's senses.
%
Such experience of disbelief suspension in \VR is what is called presence, and it can be decomposed into two dimensions: \PI and \PSI~\cite{slater2009place}.
%
\PI is the sense of the user of \enquote{being there} in the \VE, and it emerges from the real time rendering of the \VE from the user's perspective, the displayed content conforming and being consistent with the proprioception and actions of the user.
%
\PSI is the illusion that the virtual events are really happening, even if the user knows that they are not real.
%
It doesn't mean that the virtual events are realistic, but that they are plausible and coherent with the user's expectations.
%
A third strong illusion in \VR is the \SoE, which is the illusion that the virtual body is one's own~\cite{slater2022separate,guy2023sense}.
The \AR presence is far less defined and studied than for \VR~\cite{tran2024survey}, but it will be useful to design, evaluate and discuss our contributions in the next chapters.
%
Thereby, \textcite{slater2022separate} proposed to invert \PI as bring the virtual into the physical world, \ie \enquote{place it here}.
%
As with VR, \VOs must be able to be seen from different angles by moving the head but also, this is more difficult, be consistent with the \RE, \eg occlude or be occluded by real objects~\cite{macedo2023occlusion}, cast shadows or reflect lights.
%
The \PSI can be applied to \AR as is, but the \VOs must additionally have knowledge of the \RE and react accordingly to it.
%
\textcite{skarbez2021revisiting} also named \PI for \AR as \enquote{immersion} and \PSI as \enquote{coherence}, and these terms will be used in the remainder of this thesis.
As presence, \SoE in \AR is a recent topic and little is known about its perception on the user experience~\cite{genay2021virtual}.
\subsection{How Virtual is Perceived in AR}
\label{ar_perception}