A volumetric display with water drops

This project explores the possibility to build a volumetric display using waterdrops as voxels (3D pixels). Such a display would allow any number of users to correctly visualize the 3D contents without requiring any eyewear. It also allows users to reach and interact with these contents directly with their hands.

 

Motivation

Volumetric displays are a type of 3D display that allow any number of users located around them to perceive 3D contents correctly. In most planar 3D displays (3D cinema, 3D TVs, etc.), light is emitted from the display surface and specific mechanisms (shutter glasses, polarized glasses, lenticular arrays) allow specific views to reach the users eyes (i.e. each eye sees a different image).

This has two major limitations. First, the number of views is limited to a somehow reduced number. Actually, in most systems that number is two views (a left image and a right image). As a consequence all observers see the two same images, even if their position relative to the display should allow them to see a diferent perspective. Secondly, even if the 3D object we see is floating in front of the screen, the image is actually formed on the display surface. As a result, our eyes need to focus on the screen, but they need to converge in the point in front of the display where the object is floating. This is called the vergence-accomodation problem and is one of the causes of visual fatigue when viewing 3D contents (incorrect usage of the technology is another and possibly the main problem).

Volumetric displays solve these issues. Light is emitted within a volume, from the exact points where the object should appear. As a result, focus and vergence are implicitly correct. Also, the display does not only create several “views” (images from points around the 3D object), it recreates the whole object itself (the correct term would be its light-field). This allows any number of users to comfortably see the 3D contents, each from his specific position around the display.

While this technique has been succesfully applied in several displays, the usage of moving parts or even plasma to create the imagery does not allow users to reach their hands inside the volume and interact (touch) the 3D contents.

Our approach aims at creating a volumetric display allowing users to reach inside the volume. We explore the posibility of using water as the siffusing material and propose a  multilayered 3D display using water drops.

 

Our implementation is based in the approach proposed by  Barnum et. al. The display combines several pipes, with an array of nozzles placed along the pipe. A solenoid valve controls the input flow, so that only a line of droplets is released every time at a rate of 15 lines per second. The result looks like a continuous curtain of water to the human eye, even though only a few lines contain water in every instant. Several pipes are placed parallel to each other, releasing their lines with a slight time offset. This allows a single projector to illuminate the different curtains of water as the drops travel downwards.

Some images of how the contents projected on the display look:

 

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