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Portal-ble: Intuitive Free-hand Manipulation in Unbounded Smartphone-based Augmented Reality

Smartphone augmented reality (AR) lets users interact with physical and virtual spaces simultaneously. With 3D hand tracking, smartphones become apparatus to grab and move virtual objects directly. Based on design considerations for interaction, mobility, and object appearance and physics, we implemented a prototype for portable 3D hand tracking using a smartphone, a Leap Motion controller, and a computation unit. Following an experience prototyping procedure, 12 researchers used the prototype to help explore usability issues and define the design space. We identified issues in perception (moving to the object, reaching for the object), manipulation (successfully grabbing and orienting the object), and behavioral understanding (knowing how to use the smartphone as a viewport). To overcome these issues, we designed object-based feedback and accommodation mechanisms and studied their perceptual and behavioral effects via two tasks: picking up distant objects, and assembling a virtual house from blocks. Our mechanisms enabled significantly faster and more successful user interaction than the initial prototype in picking up and manipulating stationary and moving objects, with a lower cognitive load and greater user preference. The resulting system---Portal-ble---improves user intuition and aids free-hand interactions in mobile situations.