Projecting onto water for 3D show

Projecting onto water for 3D show
A team of University researchers has developed 3D images by projecting onto water droplets. The Robotics Institute at Pennsylvania’s Carnegie Mellon University says that text, video and images are created by targeting light onto and between individual water droplets. In future the technology could be used to create interactive 3D effects for theme parks, exhibitions and games.

Using a Sony Cineza VPL-HS51A LCD projector AquaLux 3D makes it possible to create three-dimensional images in water by using multiple layers of precisely controlled water droplets. Srinivasa Narasimhan, associate professor of robotics at the university said by combining the droplets with clouds of mist, it would be possible to create unique 3-D effects for theme parks, exhibitions and interactive games that don't require special eyeglasses to view, he added.

"The beauty of water drops is that they refract most incident light, so they serve as excellent wide-angle lenses that can be among the brightest elements of an environment," said Narasimhan, who developed the display with Takeo Kanade, professor of computer science and robotics, and Peter Barnum, a Ph.D. student in robotics. "By carefully generating several layers of drops so that no two drops occupy the same line-of-sight from the projector, we can use each drop as a voxel that can be illuminated to create a 3-D image."

The researchers will present a paper on the AquaLux 3D on July 27 at SIGGRAPH, the 37th International Conference and Exhibition on Computer Graphics and Interactive Techniques, in Los Angeles.

Narasimhan said work on the display technology was an outgrowth of efforts to develop an LED automobile headlight system for driving in rain at night. To eliminate the headlight reflection that can make it difficult for drivers to see in rainy conditions, they explored ways to control light so that as many rays as possible would shine between raindrops. "What we realised is that it was much easier to shine light on the drops themselves," he said.

To create a multi-dimensional display using water drops, Narasimhan, Kanade and Barnum needed to be able to target individual drops and to direct light between drops so that multiple layers of drops could be illuminated. So they developed a tightly coupled system that enabled them to generate rows of drops by using computer-controlled manifolds. By synchronising the timing of drop generation between the rows, they ensured that drops in the front rows did not block the drops in the back rows. A camera tracks the positions of the drops, so a projector can independently target each row of drops.

The system can generate drops at the rate of 60 per second, though a rate of 10 per second is sufficient for the human eye to perceive continuous resolution in each column of drops; increasing the number of drops per second increases the brightness of the display. The Carnegie Mellon researchers have demonstrated the display with four linear layers of drops and a single projector, but Narasimhan said there is no limit to the number of layers and projectors that could be employed and that the drops could be arrayed in patterns other than linear rows.

The researchers have used the water drops to display video images, text, a simulation of fish swimming in an aquarium, alternating sheets of solid colours and a multi-dimensional version of the video game Tetris.

"One unique aspect of AquaLux 3D is the potential for physical interaction," Narasimhan said. "People can touch the water drops and alter the appearance of images, which could lead to interactive experiences we can't begin to predict. We look forward to the day when creative people can fully explore the potential of this display."

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