## 5 Discussion  
The online survey and subsequent testing of various tools in the five sub-tests during the experiment show exciting findings. The charts show split ratings of designers and non-designers. In addition to the assumed differences between the two groups, higher assessment scores stand out after testing compared with before testing. A lack of knowledge concerning the new possibilities may explain the conservative attitude through the continued use of known techniques. Figure 8: (**a**) Design result of one designer; (**b**) combined designs of different citizens indicating preferred locations for new trees; (**c**) 3D heat map. Figure 7: Descriptive statistics with the non-parametric Wilcoxon rank sum test. By identifying needs through an online questionnaire and by experimentally testing tools for 3D (online) and VR through game engines, we determined the appeal and propensity to use 3D and extended reality during the public space (co-)design process among different stakeholders. The first online survey shows that almost half of the participants thought that the entire design process of public spaces would be completed in 3D within five years, and two-thirds thought that it would take another ten years. The group of non-designers was slightly more optimistic than the group of designers, presumably because the non-designers saw 3D applications in advertising, movies, and architecture, thus assuming that it is logical that it should be used for public space design as well. In contrast, designers were slightly more likely to think that it was expensive, difficult, and time-consuming. However, the online survey and experiment showed that there was such an appeal. Rethinking public space design by starting in a 3D environment whenever possible (rather than a 2D environment) is encouraged as more 3D geodata and city models of existing physical space become available as digital twins. Thanks to new interfaces and procedural modeling, the 3D co-design of future developments is gradually becoming more accessible. When citizens in 3D co-creation also add reconstructions of the past state of the public space as well as the current as-built state extracted from 3D city modeling, then, together with the animated 3D design for the future, a 4D \"Animated Spatial Time Machine\" (AntiSTMa) is created [63]. By combining the physical and virtual worlds, new hybrid 3D/4D cities are on their way to establishing a hyper-universe experience in XR [64]. From the designers' verbal responses during the experiment and afterwards, in the questionnaire, it appears that CAD, GIS, and BIM software environments are less suitable as design tools than game engines, which enable extensive, real-time 3D animations. The latter tools are not only suitable for fitting multimodal traffic flows into virtual streets but also for accommodating changing weather conditions, shadows, day/night, and seasons, as well as advanced features, such as sound, rain, and fog [8]. The growth of trees and other vegetation is usually ignored in communications about public space design, although visualization of these changes can be a powerful decision support tool [65]. In the tests, to the participants' appreciation, it was shown that trees could be enlarged more efficiently, indicating the future image after realization. For underground infrastructures, such as collectors or parking garages, and for aboveground obstacles, such as streetcar overhead wires, both of which can encumber designs, digital colliders can be provided in advance. These colliders ensure that residents and designers cannot digitally incorporate specific interventions and explain why it is technically impossible, eliminating resistance to a design proposal without prior explanation. Designer skepticism and the large gap in the adoption of 3D spatial media are partly due to the lack of or unfamiliarity with appropriate design interfaces in a 3D environment [66]. Our research has shown that the VR tool is highly valued; for many, it has been a revelation with no negative feedback.