Physical entity interactions in mixed reality (MR) environments aim to harness human capabilities in manipulating physical objects, thereby enhancing virtual environment (VEs) functionality. In MR, a common strategy is to use virtual agents as substitutes for physical entities, balancing interaction efficiency with environmental immersion. However, the impact of virtual agent size and form on interaction performance remains unclear. Two experiments were conducted to explore how virtual agent size and form affect interaction performance, immersion, and preference in MR environments. The first experiment assessed five virtual agent sizes (25%, 50%, 75%, 100%, and 125% of physical size). The second experiment tested four types of frames (no frame, consistent frame, half frame, and surrounding frame) across all agent sizes. Participants, utilizing a head-mounted display, performed tasks involving moving cups, typing words, and using a mouse. They completed questionnaires assessing aspects such as the virtual environment effects, interaction effects, collision concerns, and preferences. Results from the first experiment revealed that agents matching physical object size produced the best overall performance. The second experiment demonstrated that consistent framing notably enhances interaction accuracy and speed but reduces immersion. To balance efficiency and immersion, frameless agents matching physical object sizes were deemed optimal. Virtual agents matching physical entity sizes enhance user experience and interaction performance. Conversely, familiar frames from 2D interfaces detrimentally affect interaction and immersion in virtual spaces. This study provides valuable insights for the future development of MR systems.

Optical tracking has become the most commonly used virtual reality (VR) tracking technology because of its high precision and non-contact characteristics. The optical tracking system represented by HTC VIVE has the problem that signals of base stations interfere with each other, and the number of base stations cannot be extended by cascades, thereby limiting the scope of its work. In this paper, an extensible optical tracking system is proposed, which can distinguish the signals from different base stations and support the simultaneous operation of multiple base stations. Furthermore, we designed an encoding scheme to generate independent code for up to 32 base stations and proposed a highspeed decoding method. Experiments demonstrate that the system has high tracking accuracy and low system latency. Users can adjust the number and layout of base stations according to the actual demand, which greatly improves the flexibility of the system, and benefits promoting the development of large scale optical tracking equipment with low cost and high precision.