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

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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 simple 3D navigation interface that we augment 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 a bookmark, the camera smoothly moves from its initial position to the bookmarked point of view.
We conduct a within-subject user-study on 51 participants, where each user starts with a tutorial, and then tries successively to perform a task with and without bookmarks.
We show that not only the presence 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 streaming by replaying the traces collected during the user study, 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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