We consider that multi-scale visualization interfaces support users to view different levels of scales simultaneously and to understand large-scale, complex 3D information in 3D display environments. This article presents a user evaluation on three multi-scale interfaces on a 3D workbench display: focus + context (f + c), fixed f + c, and overview + detail (o + d). The interfaces differ in terms of (1) window arrangement and (2) positioning of detailed information relative to the user. Our goal is to identify the effect of these interface differences in large scale information visualization on a 3D workbench. To address the usability of the interfaces for a wide range of applications, we designed two tasks that differ by the level of information integration and cognitive demand. The evaluation results suggest that focus-based interfaces (i.e., the f + c and fixed f + c interfaces) are useful for tasks that require tight coupling between information layers and the o + d interface is useful for tasks performed in a densely populated information space. In terms of interface design on a 3D workbench, it is important to provide an up-close view of the current region of interest for fast scene navigation and an easy way to change viewing direction to see the 3D information from more comfortable directions. The detailed design guidelines based on the evaluation analysis are presented in this article.

We have developed a multi-user collaborative infrastructure, SCAPE (an acronym for Stereoscopic Collaboration in Augmented and Projective Environments), which is based on recent advancement in head-mounted projective display (HMPD) technology. SCAPE combines the functionalities of an interactive workbench and a room-sized immersive display to concurrently create both exocentric and egocentric perspectives. SCAPE intuitively provides a shared space in which multiple users can simultaneously interact with a 3D synthetic environment from their individual viewpoints, and each user has concurrent access to the environment from multiple perspectives at multiple scales. SCAPE also creates a platform to merge the traditionally separate paradigms of virtual and augmented realities. In this paper, we discuss the design principles we have followed to conceptualize the SCAPE system and briefly summarize SCAPE's hardware implementation. Furthermore, we discuss in detail the high-level design and implementation of the SCAPE architecture, and present a set of unique widget interfaces currently available in our implementation that enable and facilitate interaction and cooperation. Finally, we demonstrate SCAPE's unique visualization and interface capabilities via a testbed application— Aztec Explorer.