Development of a Tabletop Hologram for Spatial Visualization: Application in the Field of Architectural and Urban Design

Abstract

Architects, engineers, and designers normally visualize architectural, urban planning, urban design, or landscape design projects in different ways to present their ideas. At present, the two most widely utilized and accessible methods for spatial visualization are digital 3D modeling and physical 3D modeling. Despite their popularity, both approaches have intrinsic limitations. These shortcomings are progressively being mitigated through advancements in technology and digitalization. In this study, we propose the utilization of hologram technology as an innovative approach to overcome the limitations of both modeling methods mentioned. This research addresses two main points: the seamless integration of hologram production into the standard workflow of architectural and urban design projects, and the experimental creation of a tabletop hologram prototype using the most advanced stereoscopic visualization capabilities—CHIMERA hologram printer. The experiment’s results indicate that tabletop holograms’ visualization quality can potentially replace traditional methods in the near future. The process of creating holograms can be incorporated into the standard workflow of architectural and urban design projects and utilized in specific contexts.

1. Introduction

1.1. Three-Dimensional Visualization in the Field of Architectural and Urban Design

The necessity for 3D spatial models is evident across various disciplines including architecture, urban design, planning, landscape design, and construction. Consequently, accurate digital or physical 3D models are fundamental in the planning and development phases of these projects. The utilization of 3D models varies from the conceptualization to completion stages, each demanding differing levels of detail. In practical projects, people use 3D models as a means of communication among architects, engineers within a studio, and project stakeholders [1,2,3]. There are two main purposes for developing a digital or physical 3D model for a built environment: prototyping and showcasing projects. Prototyping is aimed at enhancing communication and consensus among designers and decision-makers. The success of projects strongly hinges on this aspect, as the concept design is adjusted based on feedback from discussions about the prototype between the two parties. This process not only helps designers quickly and effectively address the demands of investors or project owners but also eliminates potential problems that may arise during the construction stage. At the same time, showcasing projects can be explained as follows. For instance, a real estate company may require a model of their new apartment projects to provide informative presentations to their customers while marketing their products [4,5,6,7].

In the past of architectural and urban design practice, physical models were used extensively. These served as prototypes from the earliest time, allowing architects and engineers to communicate their ideas about the future built environment to non-experts such as investors and audiences. This practice has since undergone significant changes following the invention of 3D visualization software, which enables designers to showcase their conceptual project content on a screen. This shift is largely attributed to the significant reduction in processing time, manpower, and production costs associated with digital visualization. Additionally, digital tools offer greater flexibility for modifications during the design process, prompting architecture, urban planning, and landscape design studios to transition their work primarily into the virtual realm of computers. With its efficient performance, digital models have gradually replaced physical models throughout the entire prototyping process, from concept design to project completion. In the contemporary era, physical models are typically only used at the end of a project, in response to the requirements of investors or project owners, serving as stable visualizations placed in one location for other audiences. The primary purpose of physical models now lies in showcasing the investments, buildings, and built environment of the project to the public thanks to the immersive experience [1,2,4,5,7,8]. To leverage the strengths and mitigate the weaknesses of both digital and physical 3D models, a new innovation for creating 3D models with Virtual Reality (VR) and Augmented Reality (AR) is being currently hypothesized by developers. Applications where VR and AR technology are often applied in this field include the following: stake holders engagement; design support and review; consensus; operation and management support; and training education [9]. However, both VR and AR have many disadvantages that prevent them from being commercialized in the field of architecture and urbanism: high investment cost; not user-friendly; user discomfort due to motion sickness and heavy device; feeling of isolation; multi-user challenge; difficulty of achieving consensus and interaction output; difficulty of connecting to building information management (BIM); low accuracy in tracking and mapping; fully device dependence experience; expertise required for operation; lack of standardized flow for integration [9,10,11,12,13,14,15].

In addition to advancements in VR and AR technology for visualization, we propose the use of stereoscopic tabletop holograms as an innovative approach for the field of architectural and urban design. The hologram products must combine the strengths of both digital and physical models, while also being seamlessly integrated into the standard project procedures within these fields. This approach aims to enhance visualization, collaboration, and understanding in design processes. The hologram, a concept dating back to the 19th century, saw significant advancements in the past two decades, driven by significant improvements in hardware. As such, this technology has recently garnered considerable interest from researchers worldwide. However, while there have been some experiments utilizing hologram technology to visualize spatial content in architecture and urbanism, these endeavors have not yet been widely explored and remain largely open.

1.2. The Hologram as a New Approach for 3D Content Visualization

The hologram is a widely recognized technology known for its ability to make 3D content visible to the naked eye. It is often associated with its depictions in popular culture such as Princess Leia’s real-time projection in Star Wars or Iron Man’s suit visualization in the Marvel movies. In real-world applications, many perceive a hologram as a form of 3D or even 2D images appearing to hang in the air, which are often encountered in amusement parks, theaters, museums, exhibitions, and stores. However, it is important to note that although this type of visualization resembles a hologram, it typically utilizes projection technology, leading to common confusion between the two [16,17,18]. Holography, a technique based on the principle of light diffraction, began its long history of development when it was first proposed in 1947 by Denis Gabor, who developed the concept while trying to increase the resolving power of electron microscopes [17,18,19]. This achievement later earned him the Nobel Prize in 1971. This technique was later developed further by various scientists, and with the development of new diode-pumped solid-state lasers used for recording the hologram on newly developed materials such as ultra-fine grain silver halide emulsions, the recorded analog hologram can now achieve an “ultra-realistic” appearance. It is very difficult to differentiate a recorded hologram from its real-life counterpart when viewed side-by-side [20,21,22]. Despite these technological advances in holograms, hologram production has nevertheless faced challenges in the visualization of digital content in the past. For example, the applicability of holographic technology has been limited in the field of architecture, military, urban planning, manufacturing, and the automotive industry [22]. To address this and expand the range of visualized content, including digital creations of any size for diverse purposes, techniques for digital holographic stereogram printing have been evolving since the late 20th century, gradually supplanting the tasks handled by analog holograms [22,23]. From a proposal of a direct-write digital holography technique which uses object and reference beams to create a digital hologram divided into a matrix of small holographic elements (hogels) by Yamaguchi in 1995, the first generation of hologram printer was invented by Zebra Imaging Inc. in Austin, TX, USA [22,23]. However, the hologram printing speed was very slow at 2 Hz (hogels per second), and it took four days to print a 60 cm × 60 cm hologram with a resolution of 800 µm. The second generation was developed by Geola group in Vilnius, Lithuania and XYZ Imaging Inc. in Montreal, Canada [24]. Using pulsed laser-based printers, the printing speed could be up to 25 Hz; however, several other problems emerged such as a lack of color accuracy, a lack of diffraction efficiency, and a long and costly manufacturing process for the machine [22]. Finally, after 15 years of research and development, the most advanced hologram printer was then invented by Yves Gentet in Bordeaux, France. The CHIMERA hologram printer is the newest generation of holographic stereogram printers that uses low-power RGB CW lasers and Ultimate U04 ultra-fine grain silver halide holographic glass plates. This third-generation hologram printer can produce high quality, highly diffractive, large-format, full-color, and full-parallax digital reflection holograms. The printing speed is 25 Hz for 500 μm hogel resolution and 50 Hz for 250 μm hogel resolution [22].

Moreover, there are also previous hologram products created for the visualization of 3D models and presenting spatial content such as housing, construction, cities, and topography map by Zebra Imaging [25], Geola group, and Hellenic Institute of holography [26]. Using digital holographic stereogram printing techniques, Zebra produced a hologram display from various 3D spatial data, including “.obj” exports from AVEVA Review, 3Ds Max, Maya, and SketchUp; “.dwg” exports from Revit and AutoCAD; and point cloud sources from LiDAR laser scans [25,27]. Besides the model of cities and buildings, holographic maps have also been developed to deliver spatial data for various purposes like military and construction. This field was developed by the Hellenic Institute of Holography with support from the hologram printing technique of Geola group [25,28]. Because of the disadvantages of technology development and the printing quality of the 1st and 2nd generations of hologram printers, the quality of 3D spatial models with holographic display was not good enough for professional usage.

1.3. The Research Objectives and Experiment Description

In this study, we propose the utilization of hologram technology as an innovative approach to address the limitations of both digital 3D and physical 3D modeling methods. The research aims to achieve four specific objectives: (O1) Demonstrating that hologram technology can overcome the shortcomings associated with traditional visualization methods; (O2) positioning hologram technology as a viable alternative to existing VR and AR technologies; (O3) assessing the feasibility of integrating hologram visualization into the workflow of architectural and urban design projects; and (O4) qualifying the superior quality of hologram products produced by CHIMERA hologram printer technology compared to previous hologram applications in the architecture and urban design field.

To achieve seamless integration of hologram creation into architectural and urban design workflows, an experiment was conducted to create stereoscopic tabletop holograms using input spatial data. This process involves several steps: digital 3D model as input data; scale definition and scene capture; hologram printing; and hologram visualization. These steps are incorporated into the typical procedures of architectural and urban design projects, ensuring that hologram production can be effectively utilized within these fields. In the experiment, an architectural 3D model along with the landscape surrounding the building site is visualized using the hologram method on a 30 cm × 40 cm display. A U04 ultra-fine grain silver halide holographic glass plate is used as the display material for the tabletop hologram. Instead of displaying hologram content vertically as common, the hologram tabletop is placed on a flat surface and the audience can easily follow the 3D content by moving 360° around the hologram’s position. This method is particularly effective for designers aiming to visualize the master plans in architectural and urban projects. This prototype represents the first-ever tabletop hologram produced using the most advanced hologram technology specifically for architectural and urban design applications.

2. Material and Methods

2.1. The Traditional Procedure of Making 3D Models in the Urbanism and Architecture Projects

2.1.1. Project Data Source

This is also the input and foundation information of a design project. In the beginning of the workflow, two types of information will be given to the design consultants for a comprehensive understanding of the site.

(1) Preliminary data gathering: This involves gathering all relevant information such as physical characteristics in spatial data (contour lines, elevation maps, and green and blue networks in landscape), existing infrastructure (such as road systems, buildings, artificial landscape, etc.), and environmental conditions.

(1b) Terms of Reference (TOR): TOR entail different stakeholders articulating their goals and objectives for the projects.

(2) Data acquisition: Typically, the spatial data for a project are in a 2D format and are stored in various software such as AutoCAD and ArcGIS, which use a vector format, while image data are stored in raster format. As advanced methods for collecting spatial data in the form of point clouds through photogrammetry and LiDAR technology have become prevalent, architects and engineers must take an additional step to synthesize, integrate, and streamline these data to create a cohesive working environment before proceeding with the concept design phase [2,3,8,29].

2.1.2. Project Processing

This is the stage where the design consultant conducts brainstorming by sketching and building 2D drawings and digital 3D models.

(3) Conceptualization: Upon reaching a balance of different factors like the project’s goals and objectives, target audience, sustainability, and esthetic design character, architects and engineers generate their concept ideas with sketches, drawings, and 2D mappings.

(4a) Digital 3D Model: Utilizing software such as Revit, SketchUp, Blender, and 3Ds Max, architects and designers create a digital representation of the conceptualized design idea or design prototype. This step not only allows them to quickly explore design variations and adjustments, but also provides a platform for communication with other stakeholders such as investors, project owners, and other project departments (e.g., construction, marketing). There are various applications (such as Vray, Lumion, Unreal Engine, Unity) that enable designers to significantly enhance the realistic appearance of their digital model by implementing digital environments, lighting systems, materials, and textures. In addition, the 3D model plays a significant role in the subsequent steps: (4b) Consensus, where all relevant parties provide comments and feedback for the project, and (4c) Refinement, where architects and engineers collaborate on incorporating received feedback and making modifications to the designs. This entire process is repeated multiple times, typically around three times in practical design projects, until all stakeholders reach a mutual agreement [2,4,7,30]. However, during this period, consensus often occurs among highly specialized stakeholders. Simultaneously, although digital models are employed, most projects typically use 2D-rendered images derived from 3D models for client interactions.

(5a) Final design and digital 3D model: In this step, the consultant team prepares all the detailed drawings, specifications, and any necessary input for the construction phase in documentation, blueprints, and digital 3D models. After completing all the required drawings and documents, they will be sent to other departments to make basic and construction designs (5b) and for being used in construction (5c).

2.1.3. Three-Dimensional Physical Model Processing

As explained in the introduction, building physical 3D models today is in fact mostly carried out to represent works, projects, and areas that will be built in the future. Therefore, a model is considered a final prototype to exhibit to customers. Making physical 3D models also requires professionalism and high artisanship skills to achieve the required level of detail.

(6) Scale and detail definition: One of the most important considerations when creating a physical 3D model is dimensional accuracy. The ability to reference measurements is a key distinction between technical maps and models as opposed to sketches and drawings. Therefore, on the outset of this process, architects and engineers must select a suitable scale for the model based on the project and available space for display. Typically, the appropriate scales for different project types are as follows: architectural models (1:50–1:100), factories or large complexes (1:200–1:300), neighborhoods or districts (1:400–1:1000), and cities (1:1000–1:2000). Additionally, due to the differences in scale, the level of detail for the physical model must also be determined.

(7) Optimization: To ensure the physical model is as effective as possible, designers must devise an optimization plan. This plan includes decisions regarding materials, crafting techniques, the inclusion of necessary and unnecessary objects, and striking a balance between realism and esthetics. These choices are largely influenced by project owner or investor requirements, scale and detail level, professional standards, and the purpose of the exhibition. For instance, in a 1:50 architectural model created as a prototype for a real estate project targeting potential customers, the housing components, interior furniture, and construction details should be showcased. Conversely, in a city model with a 1:1000 scale, such detailed elements are omitted as they are not crucial. This optimization not only enhances the presentation of physical 3D models but also maximizes manpower and reduces model costs.

(8a) Base Map: The base map, comprising different layers from bottom to top to illustrate topography, can be created first to serve as the foundation for the physical model. Common technologies such as 3D printing, computer numerical control (CNC) milling, and laser cutting can be easily utilized to automatically generate topography layers based on input elevation data. (8b) Surface Objects: Once the ground model is complete, artists can utilize their skills to add objects to it, proceeding from bottom to top according to the detail level decided upon in previous steps. This may include elements such as traffic networks, vegetation, buildings and facilities, lighting systems, vehicles, and people.

(9) The physical 3D model is the output for this procedure. This output model is visualized with a suitable detail level of the model and accurate dimensions for measurement reference as a map.

2.2. Materials and Methods for Production of Adequate 3D Model for Hologram Printing

2.2.1. Three-Dimensional Hologram Model Data

In this study, we use one sample architectural model covered by a landscape area to test the feasibility of using a hologram printer to produce a hologram model. One advantage of a 3D holographic model over the traditional models is that the hologram printer directly reproduces the visualization model captured from the digital model created in previous steps and creates a hologram. Therefore, the optimization step for model-crafting methodology and detail-level definition is unnecessary for the hologram model, and practitioners do not have to reproduce any new content.

Numerous methods exist for creating 3D models, as discussed earlier. However, for this study, the research team focuses on developing architectural content using Autodesk software, specifically AutoCAD and Autodesk Revit. Revit, a robust 3D modeling software used in building-information management, plays a pivotal role in minimizing errors that may arise during utilization and data transfer to other software platforms. As shown in the project construction process (Figure 1), the source data for a hologram product comes from steps (4a) digital 3D model and (5a) Final design. In this research, we create an example based on the open data of a sample project belonging to Autodesk—“rac_basic_sample”, which can be found in Revit sample project files [31]. This dataset contains all the essential data required for an architecture project, encompassing elements such as project boundaries, topography including elevation and contours, landscape features, foundations, building construction details, furniture, materials, and other facilities. In terms of 3D computer applications, we employ two software tools: Revit for generating precise 3D models with accurate dimensions and Unreal Engine for incorporating realistic materials and landscapes, establishing lighting environments, and rendering the final output.

To prepare a good quality digital model for the printing step with CHIMERA, we used Revit for designing the 3D prototype from scratch, using spatial and 2D data extracted from the dataset of “rac_basic_sample”. In this step, using Revit is ideal to avoid the unnecessary heavy parts and the unwanted errors when transferring into Unreal Engine in later steps. According to the spatial information of the project boundary, contours, the construction pad stored in .dwg format that includes both dimensions, elevation, and the matching coordinates (Figure 2), we then used the construction blueprints of the house to generate the building at the location of the construction pads. In this step, the digital 3D prototype should be built carefully to maintain the accuracy. All the polygons representing different types of surfaces were defined by suitable materials in the Revit library (Figure 3). In this step, the model is not required to be realistic, because its main purpose is to simply represent the building’s shape and topography with accurate dimensions and elevation, as well as all the important 3D components and the differences in the prototype material. We then used the plugin Datasmith to transfer the whole of the construction scenes and models from Revit to Unreal Engine.

The next step involved crafting our prototype and incorporating additional elements such as vegetation, water surfaces, materials, lighting effects, and special environmental effects in real-time visualizations (Figure 4). The reason for utilizing Unreal Engine for this stage is twofold: it is easily accessible without any fees, and it offers real-time rendering capabilities. In comparison to other rendering software that relies on traditional offline rendering methods such as 3Ds Max, V-ray, and Lumion, Unreal Engine excels in rendering entire scenes, including special effects of the real environment such as reflections, shadows, and transparency. Traditional offline rendering methods can be time-consuming, especially when dealing with high-detail scenes featuring realistic materials and intricate lighting effects at high resolutions. Moreover, post-editing and environmental adjustments further extend the rendering process. Conversely, real-time editing not only allows us to observe every change in the scene as we work but also significantly reduces rendering times. Instead of rendering, we can record the scene using cameras key-framed in Sequencer along predefined paths defined by the designers [32,33]. In real-time, ray-tracing rendering techniques, the software can render images every few milliseconds (ms), achieving speeds of 16 ms per rate for 60 frames per second and approximately 33 ms per rate for 30 frames per second. The ability of Unreal Engine to deliver such high speeds in generating final images or video sequences is a game-changer for producing digital content for holograms.

2.2.2. Three-Dimensional Hologram Model Processing

As shown in Figure 1, at step (6h), Scale definition and scene capture, employing the hologram method offers several advantages over physical 3D models at this stage. First, there is no need for optimization as all content displayed in the 3D model within the software, regardless of size, can be visualized uniformly in the tabletop hologram at any desired scale. Performers are relieved of the burden of deciding which details to include or omit based on different scales, streamlining the visualization process significantly. In this research experiment, a holographic display measuring 30 cm × 40 cm was utilized, necessitating the adjustment of digital 3D content to fit within the same dimensions when determining the camera position in Unreal Engine. In addition to enabling users to observe content from all angles around the hologram tablet, it is possible to create the illusion of elements floating beyond the frame of the object with the correct digital 3D content recording and hologram printing setup. In Figure 5d, the sections of the building positioned in front of the holographic display will appear to float in the final product, while those situated behind will be depicted below the glass. In prior studies involving the creation of hologram products utilizing the CHIMERA printer, most products were designed to convey content vertically [22]. The process of recording content in software such as Blender, 3Ds Max, or Unreal Engine involves creating image sequences resembling half cylinders positioned directly in front of the object [22]. However, in this study, to capture 3D content and obtain a full parallax tabletop hologram, the image sequences are arranged to form a half sphere above the object (Figure 6). With the orientation of those virtual camera image sequence paths, the field of view of the final tabletop hologram can be up to 120° circular around the model.

The image sequences are set as circles surrounding the building, with a gradually decreasing diameter from low to high level (Figure 5a–c). These circles lie on a sphere whose center is the selected focus point as shown (Figure 5d). Therefore, the virtual camera is oriented and rotated based on the rotation axis around a focal point (Figure 5b). For this experiment, the focal point was selected to be on the first floor of the building at the building’s front. This focal point will also be situated on the plane of the hologram film plate on the display. To record and generate a 30 cm × 40 cm hologram, the configuration of the virtual camera system for rendering the model is established as follows. The distance from the virtual camera positions to the focus point is set precisely at 65 cm. The lowest level is calculated from the circle at the position where the virtual camera position is on the image sequence path creating a 60° angle with the line perpendicular to the holographic plate at the focus point position. At this level, the diameter of the circle image sequence is approximately 112.6 cm (Figure 5b,c). The total number of images captured from the virtual camera at all levels is set to 120,000 to ensure that the image data collection is equally divided for all perspectives in the sphere’s 156 levels. In practice, the number of images gradually increase as the diameter of the circle sequence image increases (note that there are 156 levels of image sequence despite the limited number of levels in the figure). This means that at the highest level at the top of the sphere, the virtual camera only takes one photo from the top view. Conversely, the highest number of photos is taken by the virtual camera located at the lowest level (Figure 5b,c). At the highest level, the number of images taken by virtual camera around the model is 1 and at the lowest level. The total number of images collected is 21,597.

The cameras rotate 360° around the building and form half a sphere, mirroring the audience’s viewing angle for the tabletop. When observing 3D content displayed in a tabletop hologram, such as architectural or urban visualization, the audience tends to move around the hologram’s location. The virtual camera’s rotation and collection of complete image data aim to create a comfortable viewing experience for the audience and minimize distortion as much as possible. Setting up image sequences for virtual camera is conducted in the Unreal Engine software. The resolution of the images is 880 × 880 pixels, and the rendering time to collect image data is approximately around 80 min for 120,000 images at 24 fps. Before moving on to the hologram printing stage, the final product can be aligned by cropping the printed content again to match. In the case of the experiment in this study, the final hologram product was cropped to a size of 30 cm × 40 cm.

As informed in Figure 1 at step (7h), Hologram printing: With the amount of scene image data collected at the end of this step, countless prints and copies of the hologram visualization can be created with the CHIMERA printer. If there is any adjustment to the digital 3D model, designers can simply adjust and repeat the image sequence rendering with the same settings. Using the hogel generation software, a hologram can be printed at different sizes, resolutions, and printing speeds [19]. In this experiment, the hologram is printed at a resolution of 250 μm with a speed of 60 Hz (60 hogels per second). The total time of printing a 30 cm × 40 cm hologram display is approximately 8.8 h. According to the methodology presented by Gentet [22], the holographic printer uses a recording system that has low-power commercial lasers. The image information corresponding to each hogel is recorded into the holographic plate using a 45° reference or zero-degree angle, depending on the purpose of the 3D content showing. As mentioned earlier in this study, the hologram is recorded on U04 silver halide holographic glass plates. After the printing finishes, the experiment practitioner has to develop the hologram with a post-processing chemical treatment. Finally, the hologram product can be sealed for protection.

2.2.3. Hologram Output

As informed in Figure 1 at step (8h), Hologram visualization: Once the 30 cm × 40 cm sealed full-color 360° full-parallax CHIMERA, recorded from the image data, is produced, an RGB LED lamp is employed to illuminate and reconstruct the hologram content. The lighting arrangement is positioned at either a 45° angle or directly perpendicular to the plane of the hologram—0°, as shown in Figure 6, depending on the angle at which the hologram was recorded in the previous step. This setup allows designers to create the desired exhibition ambiance according to their ideas.

The show case for 0° full parallax hologram can be seen in Video S1.

3. Results and Discussions

In this study, the research team conducted an experiment to visualize 3D content of a residential building and its surrounding landscape space using hologram technology. A 30 cm × 40 cm full parallax tabletop hologram was produced using the newest hologram printer technology operating at a resolution of 250 μm and a speed of 60 Hz (Figure 7 and Video S1). Through the process of conducting the experiment and analyzing the resulting holograms, the research team can address the research objectives as follows:

O1—Demonstrating that hologram technology can overcome the shortcomings associated with traditional visualization methods: Firstly, achieving the same level of expressive quality as a physical 3D model, hologram production offers significantly greater efficiency in terms of time and effort. The flexibility of holograms to freely visualize different digital content enhances their versatility compared to physical models, providing more opportunities for innovative interaction. The standardization and utilization of technology minimize the need for manual labor and reduce the risk of human error throughout the entire process. Hologram printing takes less time compared to constructing an architectural or urban model with equivalent detail. Moreover, since most of the steps of hologram production are automated, designers can allocate their time to other tasks while the machines handle the production processing time. The hologram display is thin and lightweight, with a thickness comparable to that of a sheet of glass. The hologram is printed on Ultimate U04 ultra-fine grain silver halide glass plates and the 30 cm × 40 cm version weighs approximately just less than 1 kg. When compared to digital 3D models, stereoscopic holograms provide immersive experiences for viewers through the parallax effect, akin to physical 3D models. This allows individuals who may not be proficient with 3D software to easily view and interact with the building model. Importantly, hologram tablets enable multiple people to observe the content simultaneously from different perspectives, offering a 360° viewing experience. This collective and interactive viewing capability enhances consensus and communication in architectural and urban design projects. Consequently, the flexibility in arranging the hologram presentation layout is notably enhanced. Furthermore, by employing the same hologram placement and RGB LED setup (Figure 6), multiple holograms can be seamlessly interchanged according to the designer’s preferences.

O2—Positioning hologram technology as a viable alternative to existing VR and AR technologies: Based on the widespread applications of VR and AR in architectural and urban design projects, as well as the challenges these technologies face, the research team conducted a comparative analysis with the use of holograms to evaluate their future potential (

Table 1. Comparative analysis with the use of holograms for future potential.

Usage	VR and AR	Hologram
Stake holders engagement	Yes	Prospect
Design support and review	Yes	Require more research
Consensus	Yes	Prospect
Operation and management support	Yes	Require more research
Training education	Yes	Prospect
Challenge	VR and AR	Hologram
High investment cost	Yes	No
Not user-friendly	Yes	No
User discomfort	Yes	No
Feeling of isolation	Yes	No
Multi-user challenge	Yes	No
Difficulty of achieving consensus and interaction	Yes	No
Difficulty of connecting to BIM	Yes	Yes
Low accuracy in tracking and mapping	Yes	No
Fully device dependence	Yes	No
Expertise required for operation	Yes	No
Lack of standardized flow for integration	Yes	No

Note: The usages and challenges of VR and AR technologies are according to research [9,14,15].

).

There are two critical issues to consider for the future use of holograms in architecture and urban design. Firstly, for activities such as design support, review, operations, and management support, further research is needed to enhance hologram interoperability to meet the necessary requirements. The term “prospect” is used because, to date, no practical hologram applications have been thoroughly researched in the context of architecture and urbanism. Secondly, beyond addressing the challenges outlined in Table 1, holograms currently lack the ability to interact with users in real-time, exhibit motion effects, and provide walkthrough experiences—areas where VR and AR excel. These points highlight the need for future research to develop holograms as a viable solution for architectural and urban design projects, in addition to the advancements of VR and AR.

O3—Assessing the feasibility of integrating hologram visualization into the workflow of architectural and urban design projects: During the experiments conducted with hypothetical input data from an architectural project within the scope of this research, it was observed that holograms can be seamlessly integrated into the standard project workflow. Once a comprehensive digital 3D model is created in the Unreal Engine environment, the hologram is ready for exhibition through the following three steps: Scale definition and scene capture; Hologram printing; and Hologram visualization. This entire process is largely automated through the use of specialized software and machinery, streamlining the standardized workflow and making it practical for routine use in architectural and urban design projects.

O4—Qualifying the superior quality of hologram products produced by CHIMERA hologram printer technology compared to previous hologram applications in architecture and urban design field: Through normal observation, the quality of the tabletop hologram prototype in this research experiment can be easily assessed when compared to similar hologram applications created using previous generations of hologram printers. The hologram visualization produced using CHIMERA hologram printer technology exhibits remarkable resolution and color rendition surpassing that of the Zebra Imaging hologram and products for architectural and urban projects. The resolution of the CHIMERA hologram is determined by its hogel size, which measures 250 μm. In comparison, the hogel size for a Zebra Imaging hologram is 800 μm. The CHIMERA hologram utilizes three RGB laser wavelengths—640 nm for red, 532 nm for blue, and 457 nm for green—providing higher color accuracy. [22,27]. Despite its compact size of 30 cm × 40 cm, intricate details such as blades of grass, rocks, and interior furniture are distinctly visible to the naked eye. Furthermore, environmental effects generated in Unreal Engine, such as sunlight, shadows, reflections, and water surfaces, are faithfully reproduced with high fidelity. The parallax effect remains smooth when observing the hologram from various angles owing to the image interpolation process applied during hologram data generation. The absence of noticeable distortion while navigating around and viewing the holographic 3D content further underscores its impressive quality. In this research, the hologram was created in approximately eight hours through fully automated processes using the CHIMERA printer. In contrast, holograms produced by Zebra Imaging and Geola required several days [22]. Due to the rapid speed and full automation of the CHIMERA Printer, coupled with a standardized workflow from digital 3D models to holograms, this innovative solution can be assessed for various potential applications: stakeholder engagement, consensus building, training and education, and, in the future, design support and review, as well as operation and management support.

4. Conclusions

Hologram technology represents a novel approach to visualizing architectural and urban projects, offering versatility across various applications such as professional projects, education, exhibitions, and heritage conservation. In this study, our research team successfully applied hologram methodology to depict an architectural structure and its surrounding environment. The input data comprised digital 3D content generated from Autodesk Revit and Unreal Engine software. Utilizing Unreal Engine, we created realistic environments and rendered image sequences. This hologram was printed using the latest generation of hologram printers, specifically the CHIMERA model, on Ultimate U04 ultra-fine grain silver halide holographic glass plates.

With advancements in hologram technology, computing power, and 3D software, holograms can overcome the shortcomings associated with traditional visualization methods of digital and physical models. Hologram technology should be considered a novel and viable alternative to existing VR and AR technologies in the field of architectural and urban design. Holograms have high feasibility for integration into the workflow of architectural and urban design projects. Compared to previous applications of holograms in these fields, the CHIMERA hologram demonstrates significantly higher quality. Hologram technology can also expand its capabilities by integrating with VR and AR technologies through research on hologram optical elements. This integration could pave the way for new applications in the field of architecture and urban design [34,35,36,37].

The experiment’s results highlight the potential of tabletop holograms as a new visualization method for real projects and education in architecture and urban design. Additionally, incorporating this approach into traditional project workflows is highly feasible, as the input data required for hologram technology can be fully accommodated by the existing digital 3D models commonly used in these fields. If a regular printer is considered a device that can quickly print documents, then the CHIMERA hologram printer is considered as a machine that rapidly produces 3D holograms from 3D models using standardized processes, as demonstrated in the experiments of this study. If there are any changes to the digital 3D model, operators can quickly repeat the steps for printing the hologram with full automation. Furthermore, any final hologram can be copied in a shorter time while maintaining consistent quality [38].

While the hologram representation method demonstrates clear advantages in the fields of architecture and urbanism, the research team also identified some challenges associated with this solution. First, there is the limitation of technology. Although creating high-quality holograms, as demonstrated in this experiment, has become more accessible today, the CHIMERA hologram printer remains a new technology and has not yet been explored widely in the field of architectural and urban design. Second, there are limitations in its real-time interaction capabilities. While hologram products offer immersive visualizations for digital 3D content, once the product is printed, the content becomes fixed and cannot be interacted with. Moreover, holograms provide an aerial perspective of a building or project, unlike the immersive experience of VR and AR, which offer walkthrough capabilities. This limitation reduces the user’s ability to interact closely with the building in close-up views. In the near future, as ICT and hologram technology continue to advance rapidly, successfully commercialized products will make this approach more accessible to designers, architects, and engineers. This study serves as a steppingstone for future research on applying hologram technology in architecture and urban design, aiming to address existing challenges in these fields. Future research directions in the application of holograms in this field include the following: increasing the ability to interact between users and holograms; visualizing content changes in real-time; supporting architects and designers in designing, operating and managing projects; linkable with BIM.