Urban parks are critical public spaces for physical and recreational activities ^[1][2][1,2], and they are also one of the primary elements of urban ecosystems and urban landscapes ^[3][4][5][6][3,4,5,6]. Thanks to the growth of the urban population and its social need for public open green spaces, we have witnessed an increasing demand for more citizen-centric landscape design, environmental conservation, and facility management in parks ^[7][8][7,8].

How to integrate human–environment interactions (e.g., feedback and sentiments) into environmental design or landscape renewal of urban parks is a problem being studied by various disciplines. Public participation is increasingly important in urban renewal practices as a result of urbanization, leading to a growing focus on creating a contemporary governance structure [9]. The concept of public involvement is emphasized in the participatory urban renewal strategy so that citizens can actively participate in environmental management operations ^[10][11][12][10,11,12]. Such a concept is based on communication, sharing, cooperation, and coordination, and it can give the general public the freedom to live their own lives and unleash their creative potential [13]. The early involvement of citizens in the participatory process is crucial to developing eye-level communication mechanisms between professionals and local residents, which alternates residents from the role that can only passively accept landscape changes to the active designer of the local environment [14]. The participatory workshop is the most common way for individuals to participate in such a participatory practice ^[15][16][15,16]. Through the joint participatory workshop of multiple subjects (e.g., residents, designers, and local governments), the communication between different urban governance parties in the area can be effectively improved [17].

Most studies on built environment participatory projects primarily use physical models (i.e., physical replicas) or 2D maps as tools to interact with the general public and simulate urban changes [18]. As important as these tools are, rwesearchers have witnessed an increasing number of studies using digital equipment and models (e.g., virtual 3D models) for better communication and simulation [19]. Virtual models offer the participatory process the potential of remote evaluation and near real-world sensing and perception [19]. However, most of these 3D models adopted grey boxes (without texture information) which were distinct from the actual landscapes [20]; that is, this simplified virtual 3D grey box environment cannot capture the entire essence of the built environment. Therefore, whether such models can be considered a proper tool to evoke participants’ perceptions of the actual environment is questionable.

Meanwhile, thanks to the fast development of the digital twin (a virtual representation that serves as the real-time digital counterpart of a physical object or process), studies on virtual perception based on such trending techniques are proliferating ^[21][22][21,22]. A digital twin takes a high-precision 3D virtual model as the digital base and integrates the attribute data (e.g., from physical sensors) of numerous objects in the physical space [23]. It can achieve near real-time data communication between a digital replica and the physical environment, which can support the decision-making process of environmental management for designers, residents, and the government [24]. For the participatory workshop in the context of the digital twin, high-precision replicas of the physical environment are key to encouraging public engagement and environmental scenario simulation ^{[24][25][26][27]}[24,25,26,27].

2. The Concept and Method of Participatory Design

The planning system, created by the British Urban and Rural Planning Act in 1947, was the forerunner to public participation in contemporary urban design and planning ^[28][31]. It encourages and enables the general public to voice their ideas and needs for urban development during the design process ^[29][32]. Participatory design, as an approach, is more democratic than the traditional ‘top-down’ design because it allows the public to shape places based on individual living experiences and redesign the local landscapes ^[30][33]. Presently, the ways of urban design, planning, and renewal in most Chinese cities are dominated by government guidance and policies ^[31][32][34,35]. The government-led design and planning often neglect the needs of residents, which can lead to unequal expression of interests in the local communities. Thus, social democracy is unavoidably overlooked ^[33][34][36,37]. In contrast, the ‘bottom-up’ concept rooted in the participatory approach offsets such a defect. Such participatory designs incorporate the views of professional planners, residents, governments, and other communities to cooperatively improve public spaces in the built environment and achieve the Sustainable Development Goals ^[35][36][38,39]. The consideration of ‘people’ is the core concept of the participatory approach, aiming to satisfy the needs of every ‘person’ in the design process ^[37][40]. Therefore, the participatory concept is essential to promoting social democracy. Although such a concept is still in its early stages, participatory design has gained increasing support from people with different backgrounds sround the world ^[35][38][38,41]. A large body of research has demonstrated participatory workshops to be the primary method for urban design ^[39][40][41][42,43,44]. The workshop for a particular area is often an intense multi-day design process, during which a group of experts and residents jointly develop planning strategies, taking feedback and sentiments from the general public into account ^[42][45]. Collaborations that involve, for example, urban designers, residents, and local authorities can collect in-depth knowledge about the landscape under study [10]. The workshop often includes visualizations in the form of physical or digital replicas and brainstorming on the design plans. As such, the workshop offers practical ways to take big groups on board, promote more interactive collaboration, and actively collect feedback on every minor detail ^[17][19][17,19]. Design, analysis, and negotiation are the three interconnected elements of this collaborative workshop ^[29][32]. The participatory design workshop operation requires an environment where everyone can equally express opinions and actively contribute to the discussions. Previous studies have affirmed that such interactive discussions and collaborative designing activities benefit urban planning and preserve public coherence ^[43][44][46,47]. Therefore, the regeneration of urban areas through participatory workshops has become one of the key strategies for urban development ^[10][42][10,45].

3. Digital Twin System and Virtual Participation

Recent studies have increasingly placed their interests in the methodology development of digital visualization to encourage interactive communications, such as 3D visualization ^[41][45][44,48]. Compared with conventional visualization methods such as construction plans, sections, and perspectives, near real-world 3D digital models can provide a better visualization effect [19]. A digital twin is a digital replica of a physical object, and this concept was first introduced by the National Aeronautics and Space Administration (NASA) as a paradigm for future NASA and U.S. Air Force vehicles ^[46][47][49,50]. The digital twin concept is becoming popular thanks to the rapid development of technologies that render the two-way interaction between digital replicas and the physical environment possible ^[24][48][49][24,51,52]. The 3D model can visualize spatiotemporal information in space, which allows the pre-simulation of the urban planning initiatives to identify their strengths and weaknesses before changing the physical environment ^[24][50][24,53]. Those technologies open up opportunities for the human to sense urban places in the digital models, thus suggesting the potential to encourage participation from the general public in the urban planning process ^{[20][51][52][53][54]}[20,54,55,56,57]. With the proliferation of digital twin studies, the oblique photography data that can be integrated into the models are increasingly scattered ^[55][56][58,59]. For example, a solid 3D city model based on geographic data and information, such as a digital elevation model (DEM) or a digital building model provided by regional authorities, serves as the foundation for the digital twin ^[57][60]. With unmanned aerial vehicle (UAV) oblique photography, a high-quality digital base plate for the digital twin model can also be created, yielding a fine three-dimensional genuine scene model ^[58][59][61,62]. The advancement of UAV oblique photography, as well as 3D laser modeling approaches, has aided in these multi-regional built environmental studies ^[60][61][63,64]. As a result, the UAV is now a crucial instrument for creating a digital twin city and is vital to investigating and modeling the environment ^[62][65].