Rethinking the Public Space Design Process Using Extended Reality as a Game Changer for 3D Co-Design

Abstract

Public space design processes are complex. Numerous preconditions and the involvement of stakeholders impede rapid decision making. Two-dimensional drawings remain the norm, although these are difficult for citizen stakeholders to understand. Public space designers rarely use 3D city models, infrastructure building information modeling, digital twins, or extended reality. Usually, 3D images (without animation) are only rendered after decision making for communication purposes. This study consists of an online questionnaire of 102 Flemish region (Belgium) stakeholders to show the appeal of and resistance to the use of 3D and extended reality in public space design processes. In a follow-up experiment, 37 participants evaluated various graphic techniques by their designs and observations. The questionnaire showed that all stakeholders lack experience with the use of virtual reality in design processes. We found that non-designer stakeholders and designers indicated that using virtual reality and interactive online 3D tools using game engines provided a better insight into communication and design. Reusing 3D designs in cycling simulators during the design process results in cost-effective quality optimization, and integration into digital twins or animated spatial time machines paves the way for hybrid, 4D cities. Extended reality supports 3D co-design that has simplicity and clarity from the outset of the design process, a trait that makes it a game changer.

1. Introduction

Public spaces are the realms between private domains [1]. Regardless of age, ethnicity, or physical limitations, everyone uses physical public space in all functional and physical categories to move, rest, meet, engage in recreation, or play sports [2]. Various government agencies manage public space and are responsible for its design, realization, and maintenance. As part of the urban design discipline, public space design is a complex and slow process wherein the results determine the future use of the physical world. The nature of theories of urban design, which have their roots in the humanities but extend to empirical science, links the material aspects of urban space with the social aspects of urban life [3]. Looking back in history, public space designers were predominantly seen as technicians who were almost omnipotent in public space design, using pen and paper as designing and decision-making tools; in fact, many of them still use these tools. It is striking that most current public space design processes, which have been increasingly supported by digital techniques since the 1980s, are developed in a purely 2D environment, whereas 3D technology is a primary tool that is found in most consumer products’ and architectural design processes. When citizens, the future users of the public space, are involved in participatory processes, a 3D co-design is not a standard tool.

To better understand the use of digital graphics techniques, it is first necessary to decipher the design process of urban and public spaces. Cooper et al. (2009) describe the following phases [4]:

• The survey (or pre-design phase) comprises the spatial analysis of the environment.
• The design phase includes the evaluation of various design options, the decision making, and the building permit acquisition process.
• The maintenance phase includes the realization, use, and aging process (until the start of a new design process).

The design process begins in the survey phase, which comprises a detailed spatial analysis of the existing environment in primarily 2D graphic documents (Figure 1a). The subsurface, mobility aspects, hierarchy of roads, and traffic flows are decisive elements that constrain the design options; geodata and specific datasets provide aid when completing the entire urban design survey’s spatial context. Usually, the spatial survey is limited to an objective collection of observable information about the environment. In this phase, the involvement of residents and future users is an exception.

In the design phase, initial drafts present conceptual studies based on standard profiles for classic roads or specific spatial solutions for squares and parks. Many authors have developed design principles; however, the applications often depend on the designer’s skills [5]. Carmona (2019) [6] highlights the gap between the general recognition of the minimum requirements for the design of a public space and the lack of standardized design methods. As the design process progresses and broad outlines are established, more attention is paid to incorporating and designing street furniture, utilities, and materials. Not all details are determined by the public space designer; usually, other professional stakeholders decide on street markings and traffic signals. Complex projects involve many stakeholders. During the design phase, evaluation and decision making are usually iterative steps. As Figure 1a shows, the design phase ends with technical drawings that support the building permit acquisition along with detailed plans that sustain the realization of the infrastructure [7]. As-built drawings support long-term maintenance.

The design process has not fundamentally changed since the availability of digital graphics. This research aims to portray whether technology can support citizen participation in co-designing and evolve it into a process, as presented in Figure 1b. It is necessary to unravel the evolution of digital graphic designers’ support during the survey (the pre-design) and design processes before rethinking these processes. The first digital drawings were created using computer-aided design (CAD) software and appeared in the 1980s. In the following decades, geographic information systems (GISs) increasingly offered new ways to capture data in the form of as-built plans. Three-dimensional modeling and animation software enabled a dynamic environment, and (infrastructure) building information modeling (BIM) was introduced for collaboration on 3D drawings. The addition of 3D city models laid the foundation for the development of digital twins. Animation opportunities for traffic simulations for different vehicle users and pedestrians (including accessibility for the disabled, changing weather, or seasonal conditions and noise) are now available [8]. Contrary to recent United Nations recommendations, the combination of virtual reality (VR = the experience in a completely virtual world) and augmented reality (AR = the combination of the physical world with an extra virtual representation), called mixed reality (MR), has not to our knowledge yet made its way into the public space design process [9]. Since the 1990s, a divide has emerged between public space designers and digitally inspired 3D spatial experts. Although new digital graphics tools such as extended reality (XR = the combination of VR, AR, and MR) can aid the design process, many public space designers are unfamiliar with them.

Communication and participation should be part of the design process. Moreover, designing a public space should be a transdisciplinary process involving citizens rather than an interdisciplinary process of experts, as citizens use public spaces as the end-users [10]. Usually, only one-way communication takes place after the design phase; however, interactive communication during the design process is more desirable. Participation, i.e., the opportunity for citizen consultation, is preferred but not consistently applied. Co-creation or co-design goes beyond participation by motivating citizens to design in collaboration with other citizens and designers. Organizing co-creation or co-design tends to be the exception and is limited to experimentation. Similarly, communicators for public space projects mainly include the use of 2D drawings and sometimes a few 3D images. Nevertheless, 2D plans are more difficult to understand than 3D visualizations [11]. Three-dimensional visualizations are often collages that are created using image processing software. Animated video visualizations or (online) interactive 3D environments are rarely offered. Mostly, VR applications in participation are still limited to experiments [12]. The intelligibility of graphical documents is crucial, as more and more citizens are willing to participate in urban design processes. The growth of such interactions needs to be supported. With the help of technology, a future shift from a purely physical to a cyber-physical experience of public spaces is conceivable [13].

Since the emergence of digital 3D techniques in other design domains, there has been a shift in the design process to start in 3D, from which 2D cuts and views only emerge from the 3D designs at a later stage. This research analyzes why this is not yet standard in the public space design process and whether game-changing developments can be expected using XR or online 3D. We formulated our research questions as follows: “What is the attraction and resistance of 3D and extended reality in the co-creative public space design process and how does this differ between professional designers and non-designer stakeholders?”; and “How is the use of these techniques in 3D co-creation and co-design practice appreciated?”.

The remainder of the paper is organized as follows. Section 2 provides the literature review and Section 3 explains the method. Section 4 reports the results, which is followed by the discussion in Section 5 and the conclusion in Section 6.

2. Literature Review

In our literature review, we take a threefold approach. First, urban and public space design disciplines need to be identified. The second focus is on digital developments for urban analysis, development, and design. Both relate to the full circle in Figure 1 and to the survey phase, especially the light grey sub-ring “Virtuality”. The third theme is co-creation and co-design, which corresponds to the figure’s green shell.

2.1. Urban Design for Public Space

Since the 1960s, urban design has developed into a discipline in its own right, and it is situated between urban planning and (landscape) architecture and, to some extent, overlaps these fields [14,15]. Urban design is concerned with designing neighborhoods, building blocks, streets, squares, and parks on a medium scale. Scientists primarily label urban designers as “artists”, but this is not entirely accurate in that they are subject to numerous constraints [16]. The discipline “research by design” or “design by research” is academically recognized and is located at the intersection between sketching the functional need for (public) space and the design’s visual quality [17]. Spatial research should be included at every stage of the design process, with participants collaborating and developing new knowledge [18]. Various planners, designers, and researchers have attempted to create a set of tools, parameters, normative frameworks, guidelines, or even a charter for public space rights and responsibilities in order to augment the urban space quality [6,19]. The quality of public space is not only a theoretical concept but depends on several issues that require attention [20]. In 2017, UN-Habitat’s “New Urban Agenda” drew attention to public space as there is increasing recognition of the importance of quality indicators that indicate the livability and wellbeing of cities [21]. Designers should familiarize themselves with a plethora of needs and expectations as they influence the social use of street furniture [22]. In addition, urban furniture, trees, and green infrastructure can reflect the city’s identity and location, and they are defined as aesthetics and comfort elements for walkability [23,24]. Because a public space is a multifunctional environment that is used by citizens, interdisciplinary knowledge is necessary during the design process. Designers need to shift their focus from aesthetics to a more evidence-based approach [25].

2.2. The 3D Digital Cities’ Environment

Since the turn of the millennium, 3D city models (described by many definitions, classifications, and international standards, e.g., CityGML) have outgrown 2D GIS environments and invited new spatial developments [26,27]. During the same period, 2D and 3D space syntax have supported the practice of spatial environment analyses [28,29]. BIM (built out of CAD) promotes collaboration among professional participants during the design, construction, and operation cycles of architectural and engineering projects and supports the design of public spaces [30]. Essential to public space design and infrastructure applications is the ongoing integration of GIS and (infrastructure) BIM in terms of data management and interoperability [31]. Online 3D visualizations for urban design are part of the range of possibilities [32]. Since about 2018, the digital twin concept has been applied to simulate how cities work and engage citizens to provide valuable feedback in a smart city context [33,34]. The availability of these 3D city models, which include time as the fourth dimension, is critical for urban management, despite the slowness that is caused by big data flows [35]. The application of traffic flow microsimulation software (e.g., Vissim) started at the turn of the millennium [36]. Since 2010, gamification has gained attention as a 3D simulator through the use of functions in game development software [37]. Sometimes, VR is used for visibility studies in combination with 360° cameras [38,39]. Because traffic causes noise, the soundscape design could, as an extra dimension, deliver input to urban designers in smart cities [40]. Applications for organizing street profiles in 2D, such as Streetmix, are available online for free [41]. Sometimes, apps on mobile devices try to provide solutions in consultations about projects [42]. Eye tracking could also serve as an extra tool for street redesigning. MR is not yet widely used in urban and public space design, but it could be a citizen-centric digital governance tool that could be used to bridge the gap between inhabitants and their cities [9,43].

2.3. Co-Creation, Co-Design, Crowdsourcing, Citizen Science, and Participation

E-participation in urban planning has evolved from text input over 2D digital mapping to 3D digital participatory planning and modeling [44,45]. Various forms of participatory GISs (PGISs) are possible, which are usually in 2D but sometimes already in 3D [46,47]. Participatory design is community-based, whereby the plurality of the involved actors challenges the actions’ temporal dimension [48]. Special attention must be paid to the plans’ intelligibility, as designers and citizens speak different languages [49]. In addition to “citizen science”, the term “citizen design science” has also been applied to crowd-creative urban design [50]. Decision support systems (DSSs) are used in the co-designing process and work with the public rather than for them [51]. VR as a participatory design method has attracted researchers’ attention since the turn of the millennium [52,53]. Agent-based modeling (ABM), conducted by simulating the “individual actions of various agents” combined with serious games, is also helpful in public space co-design using VR or AR [54,55]. Online participation using 3D models is slower (due to big data streaming) than today’s citizens’ expectations; however, this allows for a free and creative search for ideas and concepts that could transform the power and design quality so as to obtain excellent readability [56,57]. The human dream of a friendly city that is co-created by engaged citizens is offered an opportunity through geo-participation with gamification [58]. Furthermore, the UN-Habitat Program 2020 promoted the engagement of citizens in public space design by means of these new techniques [59]. Increasing evidence has shown that city information models (CIMs) support successful participation initiatives [60]; one of the successful initiatives for participation is the gamified use of Minecraft [61,62].

3. Methods

To answer the first research question, we set up an online survey targeting various stakeholders to investigate the propensity of using 3D and extended reality during the different phases of the public space design process. In the next step, an experiment was set up with other participants that allowed them to test five different graphic design and communication techniques that could be used in 3D co-creating and co-designing to answer the second research question. We aimed to detect the total test population’s overall appreciation of the different tools. In addition, we were curious about differences in the appreciation of tools according to designers and non-designers; descriptive statistics using the non-parametric Wilcoxon rank sum test show the result.

3.1. Assessing the Need for 3D and XR Innovations in Public Space Design Practice

An online questionnaire (conducted in August and September 2021) explicitly examined 3D and VR technology use during the public space design process in the Belgian regions of Flanders and Brussels. Through various (professional and private) channels, people were called upon to participate in an online survey. Anyone could participate in the survey and those who were involved in public design processes, especially designers, were proactively invited. The goal was to reach a large group of participants for the survey and then divide them into “designers” and “non-designers”. Typically, spatial designers acquire the skills needed to analyze, think, design, evaluate, and communicate in 3D during their education. Other stakeholders sometimes have experience with 3D data, but by default do not have the competence to create spatial designs based on the available design methodologies. Other stakeholders and citizens mostly have no experience with 3D data and certainly not with spatial design methodologies. Stakeholders who do not carry the label of “spatial designer” form the group of “non-designers”.

Our survey consisted of six question groups. There were six questions centered on the involvement of participants in public domain design processes. Eight questions provided more insight into the background of the participants, which was spread over two question groups. The two remaining question groups were polled on nine questions of the participants’ opinions on using (digital) graphic tools during design, communication, and 3D co-creation and co-design processes.

3.2. Graphic Design Tool Test

For this experiment, a call for participation was launched through various (professional and private) channels. The purpose was to test the convenience of five different graphic design tools in five sub-tests, ranging from analog 2D to digital VR when used for design, co-creation, and communication. In order to not scare off even non-digitally inclined test takers, the first sub-test method, which is familiar to all from kindergarten, was chosen: drawing with pen on paper. With each subsequent test, the presence of a digital context increased, which ended with XR. The experiment was conducted in collaboration with the city of Ghent (Belgium) and took place in one of the municipal offices. As with the online questionnaire, participants were divided into two groups: designers and non-designers. Public space designers, in particular, were encouraged to participate. The experiment took place in October 2021.

In the first sub-test, the participants worked with pen and paper in 2D. Sub-test 2 was about digital online interactive 3D being used for communication. Sub-test 3 explored online design capabilities, while sub-test 4 focused on the use of VR. Finally, sub-test 5 investigated a VR bicycle simulator. We will discuss the sub-experiments in more detail in the following sections. The tests did not focus on the design’s spatial and functional quality but rather on testing the tools. Especially, the overall impression and use of interfaces were crucial aspects here as opposed to the evaluation of the software or layout. The design of the tests is based on the lead author’s expertise in spatial design. The interfaces of the different subtests allow for an ergonomic design methodology through the availability of 3D libraries of street furniture and the assignment of functions to the control buttons of the controllers.

Afterwards, the participants anonymously evaluated the five graphical tools by means of a questionnaire on a PC in the test room. First, six questions gauged the participants’ previous experience with VR glasses and design and co-creation. Then, questions were asked about the five test setups. The usability of each tool for design and also for its use in communication was separately asked about. An overall quality rating was also gauged for each tool. The rating was placed on a 10-point scale ranging from 0 (weak) to 10 (excellent). After conducting the sub-tests, the respondents answered six more questions about their demographic and professional background. Each of the five sub-experiments and the completion of the questionnaire took 10 min per item, so the entire experiment took about 1 h to complete per participant.

3.2.1. Design on Paper in 2D

In the first sub-experiment, participants were allowed to design an (fictitious) urban square in 2D on a blind floor plan on paper (size A3) in the traditional analog way using various writing tools (markers, ballpoint pens). On this blind map, only the building lines and sidewalks were drawn without information about vertical objects. The sun icon indicated the south orientation (in Belgium). A simple 2D symbol for a tree and a bench outside was indicated on the side of the paper map. The scale (1/200) was indicated at the bottom of the map. With this limited information, participants began to work (Figure 2a). After the experience of designing on paper, subjects were also allowed to observe 2D plans and 3D simulations on paper hanging on the wall (Figure 2b) as a variant of the non-animated designs on paper before starting into animation in the subsequent sub-experiments.

3.2.2. Interactive 3D Online Viewer

In the second sub-experiment, participants did not have to perform the designing themselves but rather experienced an interactive online navigation in a 3D design on a laptop. This was visually supported by a pictured bicycle handlebar on the screen, and the participants could fictitiously cycle through newly designed public spaces in Ghent (Figure 2c). The test environment was set up in collaboration with the Department of Sports and Movement Sciences at Ghent University. Using the game engine Unity (https://unity.com, accessed on 19 June 2023), an online interactive viewable 3D model was created, animated with other road users, and put together as a WebGL build on a server of the city of Ghent. A bicycle handlebar at the bottom of the screen created the illusion that one was riding a bicycle. Arrow keys could be used to move forward, stop, and look left or right. When moving forward, the virtual bike rider would follow a preset camera path, a fixed track that was followed by the virtual bike, from which deviation was impossible.

3.2.3. Online 3D Design “Furnish-Thing!” Tool

In this sub-experiment, subjects were allowed to design public space on a laptop using a WebGL application that was developed using the game engine Unity. In this application (immediately usable by clicking on a URL without installing it on a PC), one can look around using their mouse and move around using their arrow keys. The existing physical state of a square and the new design of the public space can be alternately seen (Figure 2d–f). A library of 3D models of street furniture is included in the application, such as benches, trash cans, lighting, fountains, signage, bollards, utilities, traffic signs, and light fixtures. Various types of ground cover (textures) are also available in the application. Scale changes and rotations are possible, and objects can be moved around fairly easily. In this exercise, participants were told to primarily experience usability without focusing on creating a concrete new layout.

3.2.4. Designing with Controllers and VR Glasses in Virtual Reality

In this sub-experiment, participants were allowed to walk through a test scene using VR glasses in order to get used to the setup. The first preparatory task involved the participants exploring a virtual space and using the controllers (instead of the keyboard and mouse) to grab, move, and scale objects. The controllers in the designer’s hand became virtual hands in VR (Figure 3a). Next, the actual setup exercise began. First, the test subject virtually stood on a fictitious square with a light grey ground level and facades without texture or details in the modeling. From a 3D symbol library on the virtual square, they could select 3D objects and street furniture and reposition them on the square (Figure 3b,c). The participants were instructed on how they could move around the virtual plaza using the teleportation button on the controller. After an initial layout, facades were dressed up with more details and textures by an operator. Each participant recognized the “Veerleplein” square next to the medieval Castle of the Counts, Ghent’s most visited monument. Then, the participants could further decorate the square with more knowledge about the environment. Finally, the VR environment was supplemented by the activation of walking people, driving cars, and shade change due to the sun’s shift.

3.2.5. Animated VR Bike

Sub-experiment number 5 investigated the user experience of riding a bicycle on rollers. For this purpose, a bicycle simulator was created to test the full experience and immersion of a new street design through VR glasses (Figure 3d–f). The trackers recorded steering movements and speed while pedaling. This allowed for a quality assessment to be performed during the design process (prior to decision making). As in Test 4, two streets in Ghent were virtually reconstructed and interactive traffic animations were added using the game engine Unity. The user could cycle through two different streets. Sound sources were also added to the moving objects in this fifth test. The setup was also performed in collaboration with the Department of Sports and Movement Sciences at Ghent University.

4. Results and Analysis

In the first sub-section, we report on the online survey results that provide insight into the propensity of using (the appeal of and resistance to) 3D and extended reality during the public space design process. The second sub-section reports on the results of the five sub-tests in an experiment.

4.1. Results of the Online Questionnaire of Public Space Design Stakeholders

A total of 102 participants completed the questionnaire on graphic documents and digital graphic expertise (212 participants started but did not finish). The population includes different ages with different (and often combined) functions; A total of 72% are civil servants. The distribution of gender (58.8% male; 36.3% female; 4.9% no response) and age was fairly even; it was found that 19% of participants were younger than 34 years, 63% were between 25 and 54 years old, and 18% were older than 55 years. More important than other parameters was the decision to compare designers’ opinions (27 out of 102) with those of non-designers. This is because the public space designers (usually the plan’s drafters) have graphic training, whereas all others are citizens or stakeholders (with advisory or decision-making roles) and do not have the same professional training as designers, thus having less knowledge about graphic techniques.

Figure 4a shows how designers and non-designers feel about using 2D, 3D, and 4D (3D with the addition of animation or changes over time) during the design process. About half of all participants thought that 3D techniques should be used whenever possible. Strikingly, almost half of the designers still advocated a design process in 2D (and that 3D should only be used for communication), while only a third of non-designers shared this opinion.

Therefore, the desire for 3D is greater among non-designers than among designers, although a third of all participants considered 3D unnecessary because 2D was considered to provide sufficiently accurate impressions. A minority of less than 15% of all respondents considered 3D to be too complicated, too expensive, and too tedious. It is striking that designers were more critical than non-designers. Twenty-two percent of designers believed that 3D should only be used for large projects. A quarter of designers (and almost a third of non-designers) thought that 4D should be used. In summary, there were no essential differences between designers and non-designers; about half of both groups always wanted 3D representations.

Most importantly, about a third of all participants believed that using 3D improved the design quality. Nevertheless, some of the designers were still convinced that designing in 2D was the better option. It was found that 46% of the non-designers and 41% of the designers believed that the whole design process would be in 3D within five years; designers were the most pessimistic, with 26% believing that this would not be the case for 20 years or more. Concerning XR interfaces, less than 35% of participants used VR glasses more than once and less than 15% used AR applications or 3D CAVEs (Figure 4b–d). Notably, the group of designers scored 5% lower each time.

Concerning participation, appreciation for deploying 2D, 3D, VR, and AR systems were polled (Figure 5). Only an extreme minority thought that limited or no public participation was necessary. One fifth of non-designers valued participation by drawing on paper, while just over a third of designers found this to be sufficient. It is notable, however, that 10% more designers compared with non-designers found 2D plans to be sufficient in participation workshops. When using 2D co-design, there was no difference in appreciation between designers and non-designers; it was only a minority, and there was little enthusiasm for 2D.

The use of just a few 3D images in communication was only appreciated by one fourth of the non-designers, while almost half of the designers found it to be sufficient. There is more interest in 3D video; just under 50% of designers and about half of the non-designers favored the medium. Similar scores were observed for the use of interactive online 3D tools. 3D co-design in workshops was appreciated by half of the non-designers, whereas designers felt slightly less of a need for it. About one fifth of non-designers advocated for a 3D co-design, whereas half fewer designers advocated for it. One in three designers thought that a 3D co-design was too complicated, whereas half fewer non-designers thought the same. There was more enthusiasm for using 3D, which was always advocated by slightly more non-designers compared with designers.

Only one fourth of participants favored using VR and AR glasses in participation, with this view being shared slightly more by non-designers than designers. A third of all participants saw the benefits of AR on smartphones when communicating about new projects. There was no majority advocating the use of VR and AR in the communication and participation of the design of a public domain.

The online survey included several questions that were particularly relevant for determining the designers’ 3D expertise. For the preliminary design stage survey, more than half of the designers analyzed the surroundings in 2D, with only 10% using 3D scanning, although that number seems to be increasing. Remarkably, an overwhelming majority felt that 3D data on surrounding buildings was not crucial to the design. At the start of the design phase, most designers still designed in 2D; only 15% used a 3D symbol library. Half of the designers used 3D for volume studies and only a quarter used 3D for detail studies. Even further into the design process, 3D design is still not the standard. On the output side, a third of designers used static 3D images at the end of the design process. Only 7% used video in 3D design simulations and only 4% used interactive 3D models. A limited number of designers had experience with game engines. These results show that 2D is still the standard in the survey, design, and communication phases.

4.2. Results of the Experiment

The analyses of the experiment outcomes occurred after we split up the participants into two groups: 21 designers (with experience in public space or urban design) and 16 non-designers (residents and stakeholders) (

Table 1. Demographic distribution.

	21 Designers	16 Non-Designers (Residents and Stakeholders)
Younger than 34 years	47%	42%
Between 35 and 54 years	32%	53%
+55 years	21%	5%

).

Figure 6 shows the main results of this experiment. Participants rated their experience with the different tools on a 10-point scale for each sub-test. The reported results distinguish between designers and non-designers. For each sub-test, a graph shows the rating for both designing on the one hand and communication on the other. The rating “to design” by non-designers indicates whether the tools can be helpful for co-creation and co-design in 3D. The results of this experiment are useful for answering the two research questions that probe the attraction (or resistance to) and usability of 3D and extended reality in 3D co-creation and co-design.

The charts show a higher appreciation of digital tools compared with analog tools on paper for designing and communicating. The online 3D design “Furnish-thing!” tool was less valued than VR for designing purposes. Based on the personal communications used by the participants during the experiment, VR controllers in sub-test 4 were more user-friendly than a 2D computer mouse, as used in the “Furnish-thing!” tool in sub-test 3. The results showed a high appreciation for the VR tool for both design and communication. There was no significant difference in appreciation between designers and non-designers for digital tools. However, it is notable that 3D digital tools scored better than 2D analog tools for both groups; a non-parametric Wilcoxon rank sum test confirmed those indications (Figure 7). Even the most critical participants for 3D and VR said in verbal interviews after the experiment that they were amazed by the possibilities. The higher scores after experimenting, when compared with the online survey, indicated much ignorance about the possibilities of 3D and VR in the public space design process. Resistance is sometimes high because people have never tested these 3D and VR tools, but satisfaction increases once they have tried.

4.3. Heatmaps as a Result of the Experiment

When using 3D and VR tools, there is not only the added value of the ergonomics of the interfaces, especially for non-designers, but the additional benefit of the availability of 3D data on different stakeholders’ opinions in 3D co-creation and co-design. At the end of the experiment, participants were shown a VR implementation of their paper design from Test 1, which was created through the intervention of an operator (Figure 8a). By combining the designs of different participants in overlay, a heat map for trees or benches was created, which was also displayed in 3D (Figure 8b,c). By asking for the opinion of residents and users of the public realm at the beginning of the design process, who were considered user experts, subjective information could be gathered and delivered to the officially appointed designer to increase the co-creative level of the process (Figure 1). This new information could inspire the design process, improve the final design quality, and augment citizen involvement.

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.

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” (AniSTMa) 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. 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.

6. Conclusions

This study shows that rethinking the public space design process from an analog 2D design (created by one professional designer) to a 3D digital co-design environment is possible, although many designers still develop their designs only using paper-based methods. It has been shown that a lack of knowledge among designers, but especially among stakeholders, about 3D digital interfaces and data availability prevents the optimal use of the new tools from the beginning of the design process. Simple digital tools for designing in 3D using controllers instead of a 2D mouse are necessary and readily available. The literature review shows that this requires integrating different expertise in a transdisciplinary context.

The online questionnaire, which was used to gauge user appreciation for designing in 3D versus 2D, confirmed that there are still some barriers; however, it did confirm that all participants called for greater emphasis on 3D and VR/XR in the aspects of communication, participation, co-creation, and co-design. The complexity of design, (road) safety, transport policy, ecology, sustainability, noise, and user satisfaction, combined with the increasing demand for stakeholder consultation and participation, is leading to a growing need for better graphic representations. All stakeholders, including the designers, greatly appreciated the experiment’s online 3D and VR design tools. Real-time animations using VR simulators and the incorporation of designs into 3D city models and digital twins will result in a higher design quality. The same tools and the VR bike also received significantly high ratings for interactive communication from all subjects.

In the move towards cyber-physical public design between virtual and physical objects, our research experiment has shown that gamification (using VR and online 3D) could play a central role in the participatory 3D co-design of public spaces. The use of a game engine, in which the design and communication processes run in parallel, provides new insights into the design process. Engaging citizens in 3D co-design by using XR and 3D online interactive tools from the beginning and in all subsequent phases of a public space design process can be a game changer. This research shows that after testing these tools, the appreciation is high and the benefits are proven. Further dissemination of the knowledge about the various forms of XR among designers and non-designers is necessary to improve design quality. From a spatial policy perspective, this technology should be promoted.