Swept-volume display Swept-surface (or "swept-volume") volumetric 3D displays rely on the human persistence of vision to fuse a series of slices of the 3D object into a single 3D image. A variety of swept-volume displays have been created. For example, the 3D scene is computationally decomposed into a series of "slices", which can be rectangular, disc-shaped, or helically cross-sectioned, whereupon they are projected onto or from a display surface undergoing motion. The image on the 2D surface (created by projection onto the surface, LEDs embedded in the surface, or other techniques) changes as the surface moves or rotates. Due to the persistence of vision, humans perceive a continuous volume of light. The display surface can be reflective, transmissive, or a combination of both. Another type of 3D display that is a candidate member of the class of swept-volume 3D displays is the varifocal mirror architecture. One of the first references to this type of system is from 1966, in which a vibrating mirrored drumhead reflects a series of patterns from a high-frame-rate 2D image source, such as a vector display, to a corresponding set of depth surfaces. An example of a commercially available Swept-volume display is the Voxon Photonics VX1. This display has a volume area that is 18cm * 18cm * 8cm deep and can render up to 500 million voxels per second. Content for the VX1 can be created using Unity or using standard 3D file types such as OBJ, STL and DICOM for medical imaging. Static volume So-called "static-volume" volumetric 3D displays create imagery without any macroscopic moving parts in the image volume. It is unclear whether the rest of the system must remain stationary for membership in this display class to be viable. This is probably the most "direct" form of volumetric display. In the simplest case, an addressable volume of space is created out of active elements that are transparent in the off state but are either opaque or luminous in the on state. When the elements (called voxels) are activated, they show a solid pattern within the space of the display. Several static-volume volumetric 3D displays use laser light to encourage visible radiation in a solid, liquid, or gas. For example, some researchers have relied on two-step upconversion within a rare-earth-doped material when illuminated by intersecting infrared laser beams of the appropriate frequencies. Recent advances have focused on non-tangible (free-space) implementations of the static-volume