A team at the Public University of Navarra (UPNA), led by Doctor Elodie Bouzbib with Iosune Sarasate, Unai Fernández, Manuel López-Amo, Iván Fernández, Iñigo Ezcurdia and Asier Marzo (the latter two from the Institute of Smart Cities), has shown three-dimensional graphics floating in mid-air that people can manipulate with their hands. The system renders true 3D content without headsets and supports direct, touch-like input inside the display volume.
"What we see in films and call holograms are typically volumetric displays," says Bouzbib, the first author of the work. "These are graphics that appear in mid-air and can be viewed from various angles without the need for wearing virtual reality glasses. They are called true-3D graphics." She also highlights that "they are particularly interesting as they allow for the "come-and-interact" paradigm, meaning that the users simply approach a device and start using it."
"Commercial prototypes of volumetric displays already exist, such as those from Voxon Photonics or Brightvox Inc., but none allow for direct interaction with the holograms," the team points out. Asier Marzo, the lead researcher, comments that direct interaction means "being able to insert our hands to grab and drag virtual objects." He adds: "We are used to direct interaction with our phones, where we tap a button or drag a document directly with our finger on the screen – it is natural and intuitive for humans. This project enables us to use this natural interaction with 3D graphics to leverage our innate abilities of 3D vision and manipulation."
Here is how the tech works in simple terms. Volumetric displays use a fast-moving sheet called a diffuser. A projector sends 2880 images per second, synced to the motion of this sheet. Because of persistence of vision, separate slices at different heights blend into a full 3D volume you can see from many angles. The problem is that most diffusers are rigid, so if a hand hits the moving sheet, it can break or cause injury.
The team’s system, called FlexiVol, solves this by using elastic diffusers that people can safely press into to reach inside the volume. Volumetric displays render true 3D graphics without forcing users to wear headsets or glasses. However, the optical diffusers that volumetric displays employ are rigid and thus do not allow for direct interaction.
FlexiVol employs elastic diffusers to allow users to reach inside the display volume to have direct interaction with true 3D content. We explored various diffuser materials in terms of visual and mechanical properties. We correct the distortions of the volumetric graphics projected on elastic oscillating diffusers. As Bouzbib notes, elastic materials deform and require image correction, so the system adjusts the images on the fly.
Beyond materials, the authors propose a design space for FlexiVol, enabling gestures and actions through direct interaction techniques. A user study suggests that selection, docking and tracing tasks can be performed faster and more precisely using direct interaction when compared to indirect interaction with a 3D mouse. The team also built sample apps to show what this unlocks, including a virtual pet or landscape edition.
This innovation enables new ways to interact with 3D graphics, allowing users to grasp and manipulate virtual objects naturally. “For example, grasping a cube between the index finger and thumb to move and rotate it, or simulating walking legs on a surface using the index and ring fingers,” they illustrate.
"Displays such as screens and mobile devices are present in our lives for working, learning, or entertainment. Having three-dimensional graphics that can be directly manipulated has applications in education, for instance, visualising and assembling the parts of an engine. Moreover, multiple users can interact collaboratively without the need for virtual reality headsets. These displays could be particularly useful in museums, for example, where visitors can simply approach and interact with the content," the team added.
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