ParaFrustum: visualization techniques for guiding a user to a constrained set of viewing positions and orientations

Many tasks in real or virtual environments require users to view a target object or location from one of a set of strategic viewpoints to see it in context, avoid occlusions, or view it at an appropriate angle or distance. We introduce ParaFrustum, a geometric construct that represents this set of strategic viewpoints and viewing directions. ParaFrustum is inspired by the look-from and look-at points of a computer graphics camera specification, which precisely delineate a location for the camera and a direction in which it looks. We generalize this approach by defining a ParaFrustum in terms of a look-from volume and a look-at volume, which establish constraints on a range of acceptable locations for the user's eyes and a range of acceptable angles in which the user's head can be oriented. Providing tolerance in the allowable viewing positions and directions avoids burdening the user with the need to assume a tightly constrained 6DoF pose when it is not required by the task. We describe two visualization techniques for virtual or augmented reality that guide a user to assume one of the poses defined by a ParaFrustum, and present the results of a user study measuring the performance of these techniques. The study shows that the constraints of a tightly constrained ParaFrustum (e.g., approximating a conventional camera frustum) require significantly more time to satisfy than those of a loosely constrained one. The study also reveals interesting differences in participant trajectories in response to the two techniques.