integrating building information modeling and game ...

Proceedings of the 16th International Conference on Construction Applications of Virtual Reality, 11-13 December 2016, HK

INTEGRATING BUILDING INFORMATION MODELING AND GAME ENGINE FOR INDOOR LIGHTING VISUALIZATION Worawan Natephra, Ali Motamedi, Tomohiro Fukuda, Nobuyoshi Yabuki Division of Sustainable Energy and Environmental Engineering, Osaka University, Osaka Japan. ABSTRACT: The quality of lighting has been considered as one of the key parameters for improving human comfort. Recent advances in lighting simulation tools allow users to use Building Information Modeling (BIM) plug-ins for the lighting analysis. Although such tools enable analyzing and visualizing indoor lighting factors quantitatively and qualitatively, they do not provide an interactive environment for changing design parameters. In Addition, their visualization environment does not allow users to experience visual phenomena such as glare. This research proposes a framework for integrating BIM and Virtual Reality for indoor lighting design feedback. The research utilizes an interactive and immersive Virtual Reality environment for a realistic visualization of lighting conditions. The developed prototype system simulates daylighting and artificial lights of a designed building and visualizes a realistic lighting environment using head-mounted-displays. The system also allows a user to interact with design objects and provides real-time feedbacks. Moreover, it helps design stakeholders to better comprehend the design and improve the lighting conditions of their designs to achieve a higher degree of visual comfort for future occupants. KEYWORDS: Building Information Modeling, game engine, indoor lighting design, virtual reality, lighting design optimization, design feedback

1. INTRODUCTION There is a growing trend of utilizing computer simulation for lighting analysis based on Building Information Modeling (BIM). A number of existing commercial lighting simulation tools that are compatible with the BIM (e.g., Lighting Analysis in Revit, Lighting Assistant in 3ds Max, Radiance, Daysim and DesignBuilder) have been widely used in visualizing, identifying, and examining indoor lighting performance. The conventional lighting analysis outputs often comprise quantitative and qualitative data, and the visualization features are mainly based on static two-dimensional (2D) images. Some lighting analysis tools, such as Elumtools and Dialux, provide threedimensional (3D) visualizations and a walkthrough feature. However, such BIM tools can only present a static output with no interaction between the users and the environment (e.g., Bille et al., 2014; Kumar et al., 2011). Hence, they are inadequate for dynamically updating or changing design scenarios in real-time (Kensek et al., 2013). Another limitation of traditional tools is that designers are unable to directly experience some lighting phenomena, such as brightness, glare, or insufficient illumination, which may affect visual perception of the occupants. Consequently, utilizing each of the simulation applications aforementioned has been constrained by simulating only a static 3D model with no capability for providing a timely feedback when comparing multiple designs scenarios. In addition, while utilizing BIM and its plugins, tasks related to preparing lighting simulation and sharing the 605

Proceedings of the 16th International Conference on Construction Applications of Virtual Reality, 11-13 December 2016, HK

information between different tools are very time-consuming (Huang et al., 2008). Furthermore, for achieving a photo-realistic output, the rendering step takes a large amount of time. Conversely, game engines are designed for creating dynamic activities, interacting with objects (Edward et al., 2015) and giving an accurate and timely feedback when users interact with the building elements in a virtual environment. Therefore, coupling BIM and game engines can extend the capabilities of the BIM and make it more powerful to solve above-mentioned issues. This paper presents a framework for integrating BIM and the game engine to create real-time visualizations of indoor lighting by utilizing an interactive and immersive Virtual Reality (VR) environment. It also provides qualitative and quantitative outputs related to the lighting design. BIM database and scripting features of the game engine are utilized to create a robust prototype system for quickly performing calculation and image rendering. Using VR technology, designers are enabled to perceive realistic lighting scenes of their design. Tools such as Autodesk Revit, Unreal Engine, and its scripting environment were used in our experiments to create an interactive environment that allows to quickly update lighting scenes interactively, which facilitates comparing different designs scenarios. The main contribution of this paper is to create a new method and a tool for visualizing the lighting design by allowing users to explore their designed space, to analyze and assess lighting quality and visual comfort in a virtual environment. The applicability of the method is verified in a real-world case study.

2. LITERATURE REVIEW 2.1 Lighting Design Review in the Architecture, Engineering, and Construction industry (AEC) Lighting design, including daylighting and artificial lights relies on a combination of specific scientific principles, standards and conventions, and aesthetic (Benya et al., 2001). Five physical parameters influence occupants’ visual comfort in architectural spaces: lighting illuminance levels, lighting distribution (diffusion), Correlated Color Temperature (CCT), brightness ratio, and glare (e.g., Fielder et al., 2001; Descottes et al., 2011). Designers need to ensure that the visual comfort parameters comply with the lighting design guidelines, building regulations, and design requirements and recommendations. Visual perception describes an interpretation capability of people to visually perceive their surrounding environment. Regarding human visual perception, the most important variables are CCT and illuminance level (Shamsul et al., 2013). Lighting simulation plugins for BIM have functions to review different designs for improving lighting for the occupants. There are two different types of lighting simulation plugins compatible with BIM: external and internal plugins. The internal plugins or internal extensions can be added to BIM applications, such as Revit, and provide the highest degree of interoperability with them (Nasyrov et al., 2014). External plugins are needed for data exchange across platforms to perform simulations and visualizations. Although quantitative results are the main output of these plugins, the qualitative results, such as aesthetic, are hard to quantify (Phillips et al., 2000; Sorger et al., 2016). The simulation using traditional tools visualizes the qualitative result mainly on the basis of 2D rendered images. In addition, the simulation feature in these tools, such as Radiance, is time-consuming and not easy to use for real-time simulations (Hu et al., 2011). Collaborating with computer game environment is a new capability of BIM technology that can provide 606

Proceedings of the 16th International Conference on Construction Applications of Virtual Reality, 11-13 December 2016, HK

participants the ability to observe the facility and experience its surrounding environment before it is constructed (Figueres-Munoz et al., 2015). Coupling the game engine and BIM can create a highly interactive environment with a digital geometry model that is derived from the BIM software. Figueres-Munoz et al. (2015) investigated that the integration of BIM and gaming technology has the potential for combinatorial innovation. A number of previous research studies have proposed methods for integrating game engine, BIM, and VR experience for various purposes, such as design review (e.g., Shiratuddin et al., 2011), construction management (e.g., Bille et al., 2014), education (e.g., Wu et al., 2015), energy conservation (e.g., Niu et al., 2015), real-time architectural visualization (e.g., Yan et al., 2011), and CFD design feedback (e.g., Hosokawa et al., 2016).

2.2 Users’ Visual Perception and Lighting Design Metrics in the Game Environment The experience of virtual reality is based on the users’ perception of the virtual world (Mihelj et al., 2013). The VR technology enables the creation of very realistic models and makes the scene look real (Stahre et al., 2006). Immersion (perception) and real-time interaction (action) are two properties of the VR. VR allows users to experience an artificial environment through human senses (Souha et al., 2005). In the game environment, lighting plays a significant role in making realistic scenes. The game engine technology has lighting features that resemble real-world lightings (Shiratuddin et al., 2011). Lighting simulation in game engines can produce realistic scenes based on the inverse square law, which describes that the illumination intensity varies directly with the luminous intensity on a surface and is inversely proportional to the square of the distance between light source and the surface (IESNA, 2000; de Rousiers et al., 2014). Other lighting metrics, such as luminous flux and light color are also provided in the game engine. Luminous flux (light output or intensity), measured in lumen (lm), is to determine the quantity of light that emits from the lamp to illuminate the entire scene. The light color is expressed as color temperature (Kelvins). The advanced dynamic lighting feature in game engines provides the capability for pre-visualizing various designs. Consequently, the lighting features in game engines can be replaced with the conventional methods, which enable faster lighting simulation when changing parameters. Moreover, it is possible for players to perceive the characteristics of light to determine which design pattern is more appropriate for the users. As mentioned in Section 2.1, the illumination level and CCT are two variables that have a significant influence on human visual perception. The illuminance value is an indicator of verifying the quantity of light in a given environment, and its required range depends on types of work tasks (IESNA, 2000). International lighting standards and building regulations specify the level of illuminance required to provide visual comfort to facilitate human visual performance. CCT describes the characteristic of light colors. Color temperature plays a particularly important role in both physical properties of light and physiological and psychological response of human perception when the light enters the eyes (Shamsul et al., 2013; Descottes et al., 2011).

3. PROPOSED METHOD The proposed method comprises six major steps (shown in Fig. 1). The first step is to create the building model using a BIM software. The model data is then exported to the game engine (Fig. 1a). The second step is to setup 607

Proceedings of the 16th International Conference on Construction Applications of Virtual Reality, 11-13 December 2016, HK

the game environment to simulate various scenarios and to support interaction with users. Additional adjustments are also performed on the imported model in the game environment (Fig. 1b). Setting up the game environment to interact with the design using scripting is also performed in this step. The third step is the visualization of lighting performance, which is focused on lighting illumination (showing with false colors), brightness of artificial light sources, and lighting atmosphere (Fig. 1c). In this step, lighting simulation is done in the game environment using embedded physics engine. The fourth step is to use immersive visualizations provided in the third step to identify and analyze the performance of the lighting design by visually analyzing lighting conditions, examining visual comfort level to reach an optimum lighting design, and analyzing quantitative information and comparison (Fig. 1d). If the design is not satisfactory, the system provides a possibility to update parameters for simulating new scenarios and visualizing lighting results properly. Hence, the fifth step is to readjust design parameters, if lighting output is not satisfactory (Fig. 1e). The sixth step is to update new design parameters in the BIM after the lighting results are satisfactory for designers and users (Fig. 1f). Game Engine

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Fig. 1 Overview of the proposed method After creating an interactive virtual environment in step (b), the game engine allows to interactively explore a 3D space through Head Mounted Display (HMD), which is responding to the motion and rotation of the user’s head. Through an immersive VR environment, players can experience a lifelike sense of lighting in game scenes. Mouse and keyboard are used as the input controllers to help users navigating with the first-person perspective. Users’ avatar can see surrounding environment in the scene by HMD, which helps to perceive lighting phenomena, such as glare, that is caused by excessive luminance in the Field of View (FOV).

4. PROTOTYPE SYSTEM The developed prototype system follows the main steps shown in Fig. 2. In our prototype system, BIM model is created using Autodesk Revit (Version 2015). The geometry and material properties of building elements are modeled (described in Section 5.1). A static mesh is then created after exporting FBX file from Revit to 3ds Max. Unreal Engine is chosen as the game authoring environment in our experiment. The game environment is created by manually inputting data, such as adding materials and establishing lighting sources (artificial lights and daylight). The user interface in Unreal Engine is then set up by configuring initial parameters using visual scripts. 608

Proceedings of the 16th International Conference on Construction Applications of Virtual Reality, 11-13 December 2016, HK

This allows users to change parameters of the environment to analyze outcomes. In this step, the user can set parameters and interact with the game environment using input devices, such as a mouse and a keyboard. After setting up the parameters, the simulation is run. Simulation enables users to immediately view quantitative and visualization outputs. Users can then analyze lighting performance by comparing the results of different designs through HMD. The system allows users to redefine parameters and change scenarios until the design is approved.

Graphical User Interface (GUI) The game engine and the VR technology give users a semi-realistic sense of brightness and darkness when users are performing the walkthrough in virtual reality environment scenes. With the real-time interaction support, our prototype system supports interactivity with which users can experiment and adjust lighting or building parameters. Unreal Motion Graphics (UMG) is a visual User Interface (UI) in Unreal Engine, which is used to create various UI elements in our system. Visual scripts and graphics are used to construct the interface. The user interface is composed of eight main components that are shown on the display screen. Users can interact with game objects through a set of buttons and dialog boxes. The following interactions are supported: (a) First-person movement: to control the movement of the users’ avatar when they are walking in the design space; (b) User interface control: to customize parameters, such as time (to observe the dynamic of sunlight), lighting fixtures and light bulb types (to visualize the difference of light outputs), lighting intensity and color temperature (to observe the difference lighting appearance and illuminance level). Fig. 2 shows the GUI interface of our system. The game environment menus enable players to change input parameters and freely navigate game objects using input controllers. Several widgets are created that are shown in Fig. 2; 1) Minimap: to show the layout of furniture and the position of user; 2) Lighting intensity menu: to change the intensity of light sources; 3) Compass: to show the orientation of user when moving; 4) Color temperatures control: to change color of the light; 5) Lighting fixture types menu: to choose lighting fixtures; 6) Moving and rotation tools: to move and rotate the light source, lighting fixtures, and furniture, which are determined as game objects; 7) Material types menu: to change the material of indoor envelopes; 8) Lighting illuminance legend: to help to measure illuminance level (for false color views). 1. Mini map

7. Material choices 2. Lighting intensity

8. Illuminance legend

4. Color temperature 5. Lighting fixtures types 6. Rotate and move game objects

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Proceedings of the 16th International Conference on Construction Applications of Virtual Reality, 11-13 December 2016, HK

Fig. 2 Screenshot of the main interface of the prototype system Keyboard and mouse are used to change the view angle and to change design parameters in our system. Having false colors visualized as color textures in the 3D game environment provides users with the capability of analyzing illuminance when walking in the virtual space. The following visualization scenarios are supported: 1) Visualizing the sunlight and artificial lights when adjusting properties, time, and positions (Fig. 3b); 2) Observing the mood and atmosphere of the entire room; 3) Perceiving phenomena of excessive brightness of light sources (strong contrast between objects in the human field of vision) that may lead to discomfort (Fig. 3a); 4) Visualizing quantitative and qualitative data, such as illuminance levels (Fig. 3c). Excessive brightness and light distribution

Change of artificial light

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properties

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Sunlight simulation

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Fig. 3 Example scenes in the system

5. CASE STUDY 5.1 BIM modeling and Game Engine Integration An office room on the 4th floor of the M3 building at Osaka University, Japan was chosen as the experimentation area. The experimentation room has a typical rectangular shape, as shown in Fig. 4a. The BIM model of this room was created based on 2D CAD drawings using Autodesk Revit Architecture 2015 (Fig. 4c). The BIM model contains geometric and non-geometric information of all components, such as lighting intensity, and lighting color temperature. Fig. 4b shows the 2D plan of existing lighting fixtures. The room has 16 lighting fixtures with 32 tubular fluorescent (T8) lamps of 32W.

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3.20

Lighting fixtures

- Lighting fixture positions

(a) Photograph of the room

(b) Positions of lighting fixtures

(c) 3D BIM model

Fig. 4 Case study room In order to transfer the geometry information from Autodesk Revit to Unreal Engine, the building geometry information is needed to be transformed to a static mesh. Fig. 5 shows the process of transferring information, in which FBX file format is used to export the model from BIM application to the game engine. BIM Modeling software

Export *FBX

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Fig. 5 A BIM model transfers to the game environment Due to the the lack of full interoperability between BIM and game engine, some important information, such as material textures, color temperature, light intensity, and lighting distribution are lost while exporting data to the game engine. The lost data are required to be properly redefined.

5.2 Setting up the Game Environment 3D objects are automatically created in Unreal Engine after importing 3D geometries from the BIM application. In order to add sunlight, a directional light is added as an actor (Fig. 6a). Visual scripting is used for creating formulas for controlling yaw and pitch of the sun. Although lighting equipment and their position are successfully imported into Unreal Engine, some of their properties are not transferred. Thus, light bulbs are manually added to the game environment (Fig. 6a). In addition, lighting intensity, color temperature, and lighting profiles are manually configured by referencing from the BIM database. Fig. 6b shows a screenshot of an example of visual scripting.

Sunlight

Light bulbs

(a) Setting up light sources

(b) An example of visual scripting (Blueprint)

Fig. 6 Unreal Engine configuration

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Proceedings of the 16th International Conference on Construction Applications of Virtual Reality, 11-13 December 2016, HK

5.3 Creating Interactive Environment The visual scripting is used to create the Graphical User Interface (GUI) for supporting users’ interaction with the virtual environment for adjusting parameters (e.g., light intensity and color temperature). A set of widgets is placed on the screen. The designers can change and preview the lumen outputs and color temperatures (Fig. 7c and 7e) of a given lamp by pressing the buttons (Fig. 7a and 7b). To change the position of lighting equipment, a widget to change the coordinate of lighting fixtures and to move and rotate them is programmed (Fig. 7d).

1350 Lm

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Fig. 7 GUI for lighting fixtures setup The lighting equipment designed in the BIM application is imported into the game environment. However, additional lighting equipment items are modeled and added as alternative equipment repository. A new type of light equipment can be replaced using the GUI (Fig. 8a). Materials and textures of the indoor envelopes can also be modified using the developed widget (Fig. 8c). These features allow users to modify the design and instantly see the effect of their modification in the simulated environment. Fig. 8b and 8d show the results of simulation after properties are changed.

(b) 3D visualizations

(a) Lighting Items

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Proceedings of the 16th International Conference on Construction Applications of Virtual Reality, 11-13 December 2016, HK

(c) Material options

(d) 3D Visualization

Fig 8. Lighting fixture and material setup GUI

5.4 Lighting Design Visualization and Analysis In order to analyze lighting condition, lighting illumination, visual comfort, daylight availability, and aesthetic were focused in the case study. Fig. 9 shows an example of the illumination visualization output over time. An expert can visually observe the amount of light at different times of a day. The illuminance scenes are generated in real-time and are presented using false colors to identify patterns of insufficient illumination or possible sources of problems. Additionally, visualizing and analyzing the amount of daylight illuminations throughout the day are useful to plan for improving the use of daylighting in an effective way to reduce the energy consumption. The results of our case study showed that the working zone that is close to windows can use daylight starting from 9.00

Photorealistic visualizations

a.m. and the zone that is farther from the windows require artificial light throughout the day.

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Fig. 9 Example of the illumination visualization output In our prototype system, users can set the date and time and daylight will be automatically adjusted. Additionally, the user can interact with the lighting switches to turn them on/off using a keyboard. Shortcuts are also defined 613

Proceedings of the 16th International Conference on Construction Applications of Virtual Reality, 11-13 December 2016, HK

using visual scripting for an easier operation. In order to verify the performance of artificial lights, a simulation has been performed. The results showed that the illuminance levels in the working areas are between 450 to 500 Lux throughout. It confirms that the current lighting condition of the office areas for computer tasks satisfies the minimum standard requirements, which describes illumination levels of 300 to 400 Lux for typical open space

Photorealistic visualizations

offices (IESNA, 2000) (Fig. 10).

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Fig. 10 Lighting illumination level outputs during daytime (left) and nighttime (right) In order to validate the accuracy of lighting simulation, lighting illumination levels measured by our system and the actual site were compared. The actual illuminance was measured in several locations in the room on the horizontal plane using a light meter (CEM DT-1308 light meter (accuracy ±5%)) (Fig. 11). The measurement performed at 10.00 a.m. by turning on the artificial lights. There are no obstructions between artificial lights and the working desks. The results showed that illuminance levels measured at the work desks were approximate between 681-775 Lux (Point A to D). The illuminance level on the circulation area (Point E) was at 552 Lux. The system simulated the illuminance outputs in the range of 650-850 Lux and the illuminance levels on the circulation area were in the range of 450-550 Lux (Fig. 10). Fisher et al., (1992) recommended an acceptable error range between measurements and simulation is 10% for average illuminance calculations and 20% for each measurement point. Therefore, the error of the system is within the acceptable range.

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Proceedings of the 16th International Conference on Construction Applications of Virtual Reality, 11-13 December 2016, HK

Point E Point C

Point B

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Point A

552 Lux

775 Lux

Point C 733 Lux

Point B 681 Lux

Point D 681 Lux

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(b) Simulation results with actual illuminance levels

(a) Measurement points

Fig. 11 Measurements of actual illuminance

5.5 Discussions Providing useful quantitative and qualitative outputs, such as illumination level, lighting mood, and aesthetic for designers are major concerns in the design process. A good lighting design aims not only at creating appropriate visual conditions, which allow users to work effectively under comfortable conditions but also enhancing the comfortable feeling of the space. The visual appearance of lighting design and layers of lights, such as ambient light, accent light, task light, and decorative light can be easily previewed in the system. The main limitation was an inadequate data exchange compatibility between BIM and the game engine. Although the geometry of the model can be exchanged between BIM and Unreal Engine, many types of information such as properties of light fixtures, materials and textures were not transferred. Thus, user has to manually define bulbs and recreate textures in the game environment. Additionally, a large portion of BIM model that contains complex geometries, such as furniture models, were not transferred to the game engine. Therefore, creating simple polygon models should be considered in the modeling process. This limitation may be fixed in the new version of the application. In order to accurately perceive lighting phenomena, HMD, such as Oculus Rift DK2, with high resolution of the display screen are required. For simulating the changes of daylight, our simulation is valid only for the time duration and the season of our case study. The locations of furniture items that are directly imported from the BIM cannot be changed in our current implementation. Another limitation is that after lighting design is finalized by designers and clients, the user needs to manually update design parameters in the BIM.

6. CONCLUSIONS AND FUTURE WORK This paper investigated a method for creating BIM-based lighting visualizations for lighting performance analysis and visual comfort evaluation. The resulting prototype system has the potential for serving as a tool for visualizing lighting conditions and identifying flaws of lighting design in an immersive virtual game environment. The proposed method has been verified in a case study in a campus building. A 3D BIM model was created using Revit, and was exported to Unreal Engine. The developed tool uses VR technology to provide users with the ability to visualize lighting phenomena contributing to achieving visual comfort. Unreal Engine scripting was used to create 615

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an interactive environment that provides users with controls, which is useful for lighting design review and realtime analysis. Our initial results showed that the data can be successfully integrated. Quantitative and qualitative outputs can be used for light performance analysis and visual comfort evaluation. Automatic synchronization with the BIM database, developing a method for lighting energy feedback visualization as a real-time dashboard, and creating a sun path system to improve the accuracy of the daylight analysis will be the future work of this study.

ACKNOWLEDGMENTS This work was supported by Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Number JP2604368.

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IESNA. (2000). The IESNA Lighting Handbook. (J. Block, Ed.) (9th ed.). Newyork: The Illuminating Engineering Society of North America. Kensek, K. M. & Noble, D. E. (2013). BIM in Current and Future Practice, Journal of Chemical Information and Modeling, Vol. 53. New Jersey: John Wiley & Sons. Kumar, S., Hedrick, M., Wiacek, C., & Messner, J. I. (2011). Developing an Experienced-Based Design Review Application for Healthcare Facilities Using a 3D Game Engine, ITcon, Vol. 19, 85–104. Mihelj, M., Novak, D., & Beguš, S. (2013). Virtual Reality Technology and Applications. Springer Science & Business Media. Nasyrov, V., Stratbücker, S., Ritter, F., Borrmann, A., Hua, S., & Lindauer, M. (2014). Building Information Models as Input for Building Energy Performance Simulation – the Current State of Industrial Implementations. eWork and eBusiness in Architecture, Engineering and Construction, 479–486. Niu, S., Pan, W., & Zhao, Y. (2015). A Virtual Reality Supported Approach to Occupancy Engagement in Building Energy Design for Closing the Energy Performance Gap, Procedia Engineering, Vol. 118, 573–580. Phillips, D. (2000). Lighting Modern Buildings (1st ed.). Oxford: Architectural Press. Shamsul, B. M., Sia, C. C., Ng, Y. ., & Karmegan, K. (2013). Effects of Light’s Colour Temperatures on Visual Comfort Level, Task Performances, and Alertness among Students. American Journal of Public Health Research, Vol. 1, 159–165. Shiratuddin, M. F. & Thabet, W. (2011). Utilizing a 3D Game Engine to Develop a Virtual Design Review System, ITcon, Vol. 16, 39–68. Sorger, J., Ortner, T., Luksch, C., Schwärzler, M., Gröller, E., & Piringer, H. (2016). LiteVis: Integrated Visualization for Simulation-Based Decision Support in Lighting Design. IEEE Transactions on Visualization and Computer Graphics, Vol. 22, 290–299. Souha, T., Jihen, A., Guillaume, M., & Philippe, W. (2005). Towards a Virtual Reality Tool for Lighting, Proceedings CAAD Futures, Vienna, 115–124. Stahre, B. & Billger, M. (2006). Physical Measurements vs Visual Perception, Proceeding of CGIV, Leeds, UK, 146–151. Wu, W. (2015). Design for Aging with BIM and Game Engine Integration Design for Aging with Building Information Modeling and Game, Proceeding of 122nd ASEE, Seattle, USA. Yan, W., Culp, C., & Graf, R. (2011). Integrating BIM and Gaming for Real-Time Interactive Architectural Visualization. Automation in Construction, Vol. 20, 446–458.

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