## 5 Discussion
The VR glasses for solitary use could also be replaced by a 3D CAVE. A 3D CAVE is a box with rear projection sides spanning about three meters with one open wall; the 3D CAVE is controlled using a joystick and can be operated by multiple users simultaneously. A 3D CAVE, which is controlled by the same game engine, is as appreciated by users as VR glasses [67]. A VR bike could also be replaced by interfaces such as a VR car or walking simulator by using the same data and software without additional coding. Multimodal simulators allow any road user to make a quality assessment of the virtual design, which prevents much mischief after realization in the physical world. The addition of soundscape also increases the comparative experience value or nuisance, as this aspect would come into play after the realization of the project. The 3D designs created online and in VR can be instantly converted into a 3D print by exporting them to an STL file (the file format for 3D printing). These tactile models are essential for people with visual impairments and for those who still direct analog decision-making processes. The fact that game engines do not support geospatial file formats should not be a problem, as new assets will be made available to connect them to digital twins [68]. The data interoperability allows links to the GIS and BIM environments so that street furniture attributes can also be included in the game engine. By displaying the cost as an attribute (e.g., with a balloon) and by continuously calculating (and displaying) the total cost, the (co-)designer keeps track of indicative costs during the design process. In the future, artificial intelligence may provide additional functionalities to the parametric design that has already been applied in the tests. At the intersection of exploring new tools for spatial designers and new opportunities for improved communication and co-creation, this study examined digital technologies that are still underrepresented in spatial design processes. Within the discipline of design research, the focus is often on design methodologies and their optimization; research on digital interfaces receives little attention. In academic research on the usability of digital tools for urban development, 3D data analysis, management, and prediction in 3D city modeling, smart cities and digital twins receive sufficient attention, but spatial design scores much lower. Furthermore, for participation and co-creation, research focuses on the methods and the use of text, 2D, and non-interactive 3D images. The uniqueness of our study is the combination of these three disciplines: spatial design, digital city, and co-creation/co-design, which synchronizes the proposed solution with the disciplines. Our study has shown that the intelligibility of public space design plans is much higher when using 3D, especially VR. As intelligibility improves, the quality of participation, co-creation, and co-design also increases, which is largely due to the simplicity of VR tools. The design of street furniture and ground materials (especially the placement of road signs and line markings) could be better coordinated using VR instead of designing in 2D. All of this could contribute to an increase in the quality of public spaces.