A. Martin-Gomez, U. Eck, N. Navab Visualization Techniques for Precise Alignment in VR. A Comparative Study 26th IEEE Virtual Reality Conference, Osaka, Japan, Mar 2019 (bib)
	Many studies explored the effectiveness of Augmented, Virtual, and Mixed Reality (AR, VR, and MR respectively) for object placement tasks in assembly, maintenance, assistance, or training. Two main approaches for assisting users during object alignment exist: static visualization techniques like transparent or wireframe rendering and interactive guides such as arrows or text. In this work we focus on static visualization techniques, since they do not require precise tracking of the objects that need to be aligned. To the best of our knowledge, no previous work exists that evaluates which visualization technique is most suitable to support users while precisely aligning objects using AR. This paper presents a comparative evaluation of four visualization techniques used to render virtual objects when precise alignment in 6 degrees of freedom (DoF?) is required. The selection of these techniques is based on the amount of occlusion observed when the real and virtual objects overlap. We propose using two visualization techniques presenting low amount of occlusion: Silhouette and Fresnel-Derivative, and we compare them against two commonly used techniques: Wireframe and Semitransparent. We designed a VR environment considering two scenarios –with and without time constraints– in which users aligned pairs of objects. To evaluate users performance, quantitative –distance, rotation and time to completion–, and qualitative –usability and mental effort– scores were collected. Our results suggest that the selection of visualization techniques with low levels of occlusions can improve the precision in rotation and translation achieved by users and increase the usability of the systems.
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