ISSN : 1796-2048
Volume : 1    Issue : 3    Date : June 2006

Probabilistic Algorithms, Integration, and Empirical Evaluation for Disambiguating Multiple
Selections in Frustum-Based Pointing
Greg Schmidt, Dennis G. Brown, Erik B. Tomlin, J. Edward Swan II and Yohan Baillot
Page(s): 1-12
Full Text:
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There are a few fundamental pointing-based user interface techniques for performing selections in
3D environments. One of these techniques is ray pointing, which makes selections by determining
intersections of objects along a single ray cast from the user. This technique is susceptible to
inaccuracy of the user interface tracking technology and user noise (e.g., jittery hand, see actual
viewing ray in Figure 1 (bottom) and how it misses the object when error is factored in). Another
technique is the frustum-based (or equivalent cone-based) approach which casts a frustum from
the user into the 3D scene. Selections are made by performing intersections of objects with the
frustum. This technique resolves the imprecision associated with the ray pointing technique (see
how the lightly shaded cone in Figure 1 (bottom) still intersects the object), but may produce
multiple ambiguous selections as shown in Figure 2. This paper presents probabilistic selection
algorithms and integration schemes that address some of the ambiguities associated with the
frustum-based selection technique. The selection algorithms assign probabilities that the user has
selected particular objects using a set of low-level 3D intersection-based selection techniques and
the relationship of the objects in a hierarchical database. Final selections are generated by
integating the outputs from each selection algorithm using one of several weighting schemes. We
implemented the selection algoithms and weighting schemes within our distributed augmented
reality (AR) and virtual reality (VR) architecture. Next, we performed several experiments to
empirically evaluate the probabilistic selection techniques and integration schemes. Our results
show that the combined selection and integration algorithms are effective at disambiguating
multiple selections. This paper thoroughly describes the architecture, experiments, and results.

Index Terms
interaction, selection, algorithms, augmented reality, virtual reality, hierarchical databases