As a part of its corporate social responsibility, Korea Hydro & Nuclear Power decided to donate a unique full sphere theater Space 360 to one of the national science museums in Korea. The company, which is Korea’s national operator of power plants, wanted to surprise visitors with a completely new experience – enjoying an immersive environment without any VR headsets. Front Pictures won a tender for engineering and installing the projection system and software for this installation.
The spherical projection theater located in front of the Gwangju National Science Museum
Space 360 – which is 12 meters in diameter – is located next to Lucerium National Science Museum in Gwangju. Construction started in September 2016 and finished in July 2017. The sphere opened for visitors in September 2017.
This spherical projection theater can be considered a true VR theater of the future. When visitors step inside, they find themselves on a transparent glass observation bridge, which crosses the sphere’s interior. A crisp 360 video projection around, above, and below the viewers fully immerses them as they stand and watch. They literally dive into a virtual world without having to use VR headsets.
Full spherical projection theaters can be considered movie theaters of the future. Unfortunately, they are still very rare in the world. Most of them are experimental one-of-a-kind installations utilizing technologies that are already outdated.
Our aim was to create a projection sphere of the next generation by accumulating the world’s best practices and implementing the newest technologies. We wanted to make a true VR theater that would give visitors a breathtaking 360 immersive experience. But to meet our idea of the future, the system also needed to have the highest possible resolution and brightness of projection, high energy efficiency and cost effectiveness.
Gwangju National Science Museum – client.
Korea Hydro & Nuclear Power Co. – sponsor.
Front Pictures (Ukraine) – projection system design and installation, A/V engineering, media-servers and software.
Redrover (South Korea) – system integration, screen manufacturing, and content production.
EL Architects (South Korea) – construction design.
Baekje (South Korea)– construction.
Front Pictures has vast experience in engineering fulldome theaters and planetariums. By the mid 2017, the company has delivered around 150 fulldome systems to many countries around the world. But when designing the projection system for Space 360, the company’s team had to come up with unique technological and engineering solutions.
Unlike in a conventional digital planetarium, where projectors are located along the dome’s perimeter, the options for placing thеm in a full sphere are substantially limited. One of the challenges was to devise a layout that would avoid shadows being cast by the observation bridge, minimize openings for the projectors, while, at the same time, maximizing the resolution and brightness of the projection. It was also important to position the projectors in a way that would prevent them from shining light into the viewers’ eyes.
Choice of projectors and their layout
Taking all the factors into account, Front Pictures team decided to use 12 projectors and locate them around two entrance doors.
Our engineers devised a dozen types of projection layouts. We were considering models from four different vendors.
We used precise 3D models of the venue and calculated each projector position and tilt taking into account taking into account its aspect ratio, resolution, and available lenses. The projector size was taken into consideration as well, because of the limited space behind the spherical screen where the projectors had to be located. Price constraints were also important for meeting the budget.
After doing research, Front Pictures opted to use Barco PGWU-62L WUXGA projectors with a laser phosphor light source. This model was chosen for the following reasons:
1) Thanks to laser phosphor technology, the projectors support 360° rotation. This was a decisive factor because some projectors needed to be rotated at extreme angles. Lamp free technology also ensures a long, up to 20,000-hour, light source lifetime and reduces maintenance costs.
2) The model has a lightweight and compact design that facilitated the installation in the confined space behind the projection screen. The low noise level was also important in the enclosed environment with many projectors running simultaneously.
3) Projectors’ 16:10 frame aspect ratio provides optimal pixel overlapping. Thanks to the 1920х1200 resolution multiplied by 12 projectors, we obtained a sufficient pixel density across 450 sq. meters of the spherical screen. The total number of pixels is 27.6 MP, effective pixels (excluding overlapping) – 18.8 MP (6x3K).
The spherical screen creates significant geometrical distortions of the projected image.
The distortions become even larger due to the fact that in a full projection sphere, it is impossible to place projectors along the perimeter, as a sphere has no edge. They need to be located around the entrance doors on the opposite sides of the sphere.
This scheme has many advantages, but positioned this way, projectors create uneven and elongated spots of light with uneven pixel density and brightness. The task of creating a seamless picture with uniform brightness becomes even more challenging when the projected images overlap with each other in this way.
In this situation, manual calibration (stitching images together) is not the best option. Instead, we adopted an automated calibration system, based on powerful computer vision and image analysis algorithms combined with a 360 degree multiple camera rig.
Front Pictures has been developing auto-calibration technology since 2012 as a part of its Screenberry media server. The auto-calibration process usually requires a video or DSLR camera. The lens’s field of view should be wide enough to “see” the whole screen. The camera records a series of calibration patterns projected onto the screen. Auto-calibration software analyses patterns to seamlessly blend projectors together into a unified coordinated space.
For a conventional fulldome (half sphere), one camera with a fisheye lens is required. But one camera is not enough to completely cover the spherical screen with a bridge in the center.
To overcome that, we used four cameras with fisheye lenses mounted around the glass bridge. We opted for Nikon D610 full frame DSLR cameras for their high resolution and excellent low-light performance. Consequently, we had to customize our software to enable the multi-camera calibration.
The previous generation of multi-projector systems were built around the “one computer per one projector” paradigm. But this approach has significant drawbacks such as a relatively big budget for computer hardware, more possible points of failure, difficulties with implementing proper failover solution, as well as higher electricity consumption. Another downside of the cluster systems is a discrepancy in video playback speed on different computers, which can result in rough, jerky video playback.
An alternative to the multi-server system is a single server approach. At Front Pictures, we’re advocating for a one-server multiple-outputs paradigm. In 2010, we developed a video engine which can use every single bit of power of the media-server hardware and process extremely high resolution media in real-time. Thanks to efficient render engine, we can handle many more displays per single machine than most other solutions available on the market. Now, this technology called Screenberry media server can smoothly playback 8x8K video on up to 72 output devices, all the while connected to just one computer.
The Screenberry media server is a hybrid video processing engine which uses both the GPU and CPU in a very effective manner. This approach allowed us to achieve high levels of performance by using reliable commodity hardware. It also helped to reduce the server’s price and maintenance costs.
Media server configuration:
GPU: nVidia GTX1080-8G
CPU: Intel Core i7-5960X
RAM: DDR4 64GB
Data storage: 1TB SSD
Audio Interface: RME M-16 DA + RME HDSPe MADI Card
Three high resolution signals of a single GPU are split into 12 WUXGA outputs with the help of 3 x Datapath Fx4 – the latest model from the line of Datapath video wall processors.
The media server can play standard 360 VR (equirectangular) format video or 2x Dome Master video files. The server also supports external video signal capture as well as web streaming.
Screenberry is also responsible for 10 channel audio playback.
In March 2017, our team visited the construction site in Gwangju to double-check the measurements and finalize the setup schedule for the projection system.
The installation began on June 1, 2017 and took two weeks. During the first five days the team installed projectors, power and video cables, and a media server rack. Thanks to the high precision of our technical drawings, all the projectors ideally fit their slots, providing the required projection parameters.
This first stage was followed by the autocalibration system setup, which took another seven days. Equipment testing and personnel training required two more days.
Calibration test pattern
During the projection system setup, the production studio Redrover tested the content exclusively created for the sphere. The show narrates the history of the world, starting from the Big Bang to the origins of life and onto human civilization. It also tells visitors about energy and green technology.
The work on the spherical projection theater was finished on July 27th, 2017. The sphere began to welcome visitors on Sept 5th, 2017.