Object sliding and beyond: Investigating object manipulation in 3D user interfaces

3D manipulation is one of the fundamental tasks for interaction in virtual environments. Yet, it can be difficult for users to understand the spatial relationships between 3D objects and how to manipulate them in a 3D scene, as, unlike in the physical world, users do not have the same visual cues for understanding scene structure or can leverage constraints and affordances for interaction. My goal is to create better user interface for 3D manipulation platforms, with a focus on positioning objects. I designed efficient, accurate, and easy-to-use 3D positioning techniques for both desktop and virtual reality (VR) systems. My work also contributes guidelines for designing and developing 3D modelling software for desktop and VR systems, and enable 3D content designers, game designers, or even novice users to benefit from improved efficiency and accuracy for 3D positioning tasks. Much of my thesis work builds on a 3D object sliding technique, where objects slide on surfaces behind them, which helps with some positioning tasks. First, I improved 3D positioning on a desktop system, with the mouse and keyboard as input devices. I presented two new techniques that significantly outperform the industry-standard widget- based 3D positioning technique for tasks involving floating objects or objects that can be at multiple positions in visual depth. Second, I proposed a new technique that allows users to select and position hidden objects. The new technique also outperformed 3D widgets. Then, I applied my techniques in a VR system with a head-mounted display (HMD) and compared the performance of different input devices. I found that the combination of the mouse with my new positioning technique is still the best solution, even in VR. In the remainder of my thesis work, and focusing on tasks involving more distant objects, I investigated manipulation techniques in VR that do not rely on the availability of a mouse. I designed and implemented a technique that significantly improved the accuracy for 3D positioning tasks for targets that were in contact with the scene.