  We propose and study a novel cross-reality environment that seamlessly
integrates a monoscopic 2D surface (an interactive screen with touch and pen
input) with a stereoscopic 3D space (an augmented reality HMD) to jointly host
spatial data visualizations. This innovative approach combines the best of two
conventional methods of displaying and manipulating spatial 3D data, enabling
users to fluidly explore diverse visual forms using tailored interaction
techniques. Providing such effective 3D data exploration techniques is pivotal
for conveying its intricate spatial structures -- often at multiple spatial or
semantic scales -- across various application domains and requiring diverse
visual representations for effective visualization. To understand user
reactions to our new environment, we began with an elicitation user study, in
which we captured their responses and interactions. We observed that users
adapted their interaction approaches based on perceived visual representations,
with natural transitions in spatial awareness and actions while navigating
across the physical surface. Our findings then informed the development of a
design space for spatial data exploration in cross-reality. We thus developed
cross-reality environments tailored to three distinct domains: for 3D molecular
structure data, for 3D point cloud data, and for 3D anatomical data. In
particular, we designed interaction techniques that account for the inherent
features of interactions in both spaces, facilitating various forms of
interaction, including mid-air gestures, touch interactions, pen interactions,
and combinations thereof, to enhance the users' sense of presence and
engagement. We assessed the usability of our environment with biologists,
focusing on its use for domain research. In addition, we evaluated our
interaction transition designs with virtual and mixed-reality experts to gather
further insights.
