Fitted avatars: automatic skeleton adjustment for self-avatars in virtual reality

Abstract

In the era of the metaverse, self-avatars are gaining popularity, as they can enhance presence and provide embodiment when a user is immersed in Virtual Reality. They are also very important in collaborative Virtual Reality to improve communication through gestures. Whether we are using a complex motion capture solution or a few trackers with inverse kinematics (IK), it is essential to have a good match in size between the avatar and the user, as otherwise mismatches in self-avatar posture could be noticeable for the user. To achieve such a correct match in dimensions, a manual process is often required, with the need for a second person to take measurements of body limbs and introduce them into the system. This process can be time-consuming, and prone to errors. In this paper, we propose an automatic measuring method that simply requires the user to do a small set of exercises while wearing a Head-Mounted Display (HMD), two hand controllers, and three trackers. Our work provides an affordable and quick method to automatically extract user measurements and adjust the virtual humanoid skeleton to the exact dimensions. Our results show that our method can reduce the misalignment produced by the IK system when compared to other solutions that simply apply a uniform scaling to an avatar based on the height of the HMD, and make assumptions about the locations of joints with respect to the trackers.

Stretch your reach: Studying Self-Avatar and Controller Misalignment in Virtual Reality Interaction

“…This focus means our findings might not fully represent the variety of experiences in VR applications. For instance, in scenarios without active interaction, users might be less likely to notice the incorrect alignment of virtual and real hands, as suggested by Ponton et al [32].…”

“…Note that if the virtual arm were longer than the real hand, the result would be that the IK would bend at the elbow to reach the end-effector. This situation does not prevent the user from reaching objects, it simply introduces a mismatch in the pose of the arm [32], but not in the position of the end-effector.…”

“…In these cases, the upper body is located under the HMD position, and the virtual hands are rendered at the position of the handheld controllers, and provide a way to interact with the virtual world. However, when rendering a full virtual body, it is often difficult to accurately co-locate the virtual and real hand positions due to limitations of the virtual body, such as body size or proportions [33], skeleton simplification, or inaccurate offsets with respect to trackers [32]. Respecting the virtual body dimensions may lead to misalignments between the virtual hand/controller and the real hand/controller when reaching far-away objects.…”

“…Body discrepancies may not be perceptually noticeable in applications that do not require careful manipulation of objects, for example, those where the user has to move freely [32], walk [23], gesticulate while talking [39], or even hold a controller and eventually press a button [27]. However, when direct manipulation is needed while rendering a full avatar, it may be necessary to redirect the hand position to respect the limits imposed by the virtual body.…”