\chapter{Bookmarks, navigation and streaming\label{bi}}

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\begin{figure}[th]
    \centering
    \begin{subfigure}[b]{0.45\textwidth}
        \includegraphics[width=\textwidth]{assets/preliminary-work/bookmarks/camera-bookmark.png}
        \caption{Viewport display of a bookmark}
    \end{subfigure}
    \begin{subfigure}[b]{0.45\textwidth}
        \includegraphics[width=\textwidth]{assets/preliminary-work/bookmarks/arrow-bookmark.png}
        \caption{Arrow display of a bookmark}
    \end{subfigure}

    \begin{subfigure}[b]{0.45\textwidth}
        \includegraphics[width=\textwidth]{assets/preliminary-work/bookmarks/arrow-bookmark-with-preview.png}
        \caption{A preview is shown when the mouse hovers over a bookmark}
    \end{subfigure}
    \begin{subfigure}[b]{0.45\textwidth}
        \includegraphics[width=\textwidth]{assets/preliminary-work/bookmarks/arrow-bookmark.png}
        \caption{A coin is hidden behind the curtain\newline}
    \end{subfigure}
    \caption{3D bookmarks propose to move to a new viewpoint; when the user clicks on the bookmark, his viewpoint moves to the indicated viewpoint.\label{bi:bookmark}}
\end{figure}

% Bookmarks are virtual objects that represent a point of view, that are rendered with the scene and that can help user navigation.
In this chapter, we present our first contribution: an analysis of the impact of bookmarks on navigation and streaming.

We implement a 3D navigation interface where the keyboard translates the camera and the mouse rotates it.
We augment this interface with 3D bookmarks.
When the user's cursor hovers over a bookmark, a preview of the point of view is displayed to the user, and when the user clicks on a bookmark, the camera smoothly moves from its current position to the bookmarked point of view.
We conduct a within-subject user-study on 51 participants, where each user starts with a tutorial to get used to the 3D navigation controls, and then tries successively to perform a task with and without bookmarks.
We show that not only the presence of bookmarks causes a faster task completion, but also that it allows users to see a larger part of the scene during the same time span.

However, in a streaming scenario, this phenomenon leads to higher network requirements to maintain the same quality of service\todo{not sure if service or experience}.
In the last part of this chapter, we simulate a streaming setup and we show that knowing the positions of the bookmarks beforehand allows us to pre-compute information that we can reuse during streaming to compensate for the harm caused by the faster navigation with bookmarks.

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