The demand for participant engagement in urban planning shows a great need for tools that enable communication between stakeholders and make planning processes more transparent. So far, common methods use different tools and platforms independently. This prevents the full potential for effective, efficient, and creative collaboration from being realized. Hence, this paper presents an approach that combines different participation settings (off-site, on-site, and online) by using an interactive touch table and an additional screen, as well as virtual reality (VR) and augmented reality (AR) devices, and synchronizing them in real-time. To fulfill the collaboration requirements, three major technical aspects are addressed in the concept and prototype implementation: Firstly, the demands for various settings and devices require a uniform and cross-device interaction concept. Secondly, all changes in the course of the participation (e.g., adding, manipulating, or removing objects) must be synchronized across all devices in real-time, with very low latency. Thirdly, the various states should be saved persistently during the collaboration process. Detailed empirical usability studies are still pending; however, pretests indicate that the concept is appreciated, and the transferability to other planning processes is given.

Due to the growing number of users, social virtual reality can get crowded. As we sometimes prefer to be only surrounded by friends or more enjoy empty galleries to have a better view, we designed SocialSlider: an interaction technique that allows us to manipulate other avatars’ transparency. We implemented SocialSlider with two transparency control modes and four avatar selection techniques: (1) select a single avatar, (2) select all, (3) select a co-located group, or (4) select a semantic group, such as unknown users. Through a user study, we found that (A) The concept of SocialSlider is appreciated and promising to overcome issues of crowded VR, such as occlusion. (B) The avatar’s level of transparency can affect their perceived co-presence. Thus, we show that fading avatars’ visibility is a beneficial technique in multi-user VR with benefits beyond avoiding occlusion, such as controlling the felt privacy or the experience of being social.