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[[Image:CAVE Crayoland.jpg|thumb|The CAVE, showing the stereoscopic projection on the walls.]]

[[Image:CAVE Crayoland.jpg|thumb|230px|A CAVE, showing the stereoscopic projection on the walls.]]

A '''cave automatic virtual environment''' ('''CAVE''') is a [[virtual reality]] environment where [[digital projector|projectors]] show images on the walls of a room. The images are projected to at least three of the walls of a room-sized cube. The name is a reference to the allegory of the Cave in Plato's ''Republic''.

A '''cave automatic virtual environment''' ('''CAVE''') is a [[virtual reality]] environment where stereoscopic images are shown on the walls of a room. The images are projected to at least three of the walls.

The CAVE was invented at the [[University of Illinois, Chicago]] [[Electronic Visualization Laboratory]] in 1992.<ref>{{cite journal|last1=Cruz-Neira|first1=Carolina|last2=Sandin|first2=Daniel J.|last3=DeFanti|first3=Thomas A.|last4=Kenyon|first4=Robert V.|last5=Hart|first5=John C.|title=The CAVE: Audio Visual Experience Automatic Virtual Environment|journal=Commun. ACM|date=1 June 1992|volume=35|issue=6|pages=64–72|doi=10.1145/129888.129892|s2cid=19283900 |issn=0001-0782|doi-access=free}}</ref> The images on the walls were in stereo to give a depth cue.<ref name="Carlson 2017 c094">{{cite web | last=Carlson | first=Wayne E. | title=17.5 Virtual Spaces | publisher=The Ohio State University | date=2017-06-20 | url=https://ohiostate.pressbooks.pub/graphicshistory/chapter/17-5-virtual-spaces/ | access-date=2024-04-12}}</ref>

The images can be stereoscopically polarized or done using [[shutter glasses]].

==General characteristics==

==General characteristics==

The walls of a CAVE are typically made up of [[Rear-projection television|rear-projection]] screens, however large-scale [[LED display|LED displays]] are becoming more common. The floor can be a downward-projection screen, a bottom projected screen or a flat panel display.  The projection systems are very high-resolution due to the near distance viewing which requires very small pixel sizes to retain the illusion of reality.

The walls of a CAVE are typically made up of [[Rear-projection television|rear-projection]] screens. The floor can be a downward-projection screen, a bottom projected screen or a flat panel display.

The user wears 3D glasses inside the CAVE to see [[3D graphics]] generated by the CAVE. People using the CAVE can see objects apparently floating in the air, and can walk around them, getting a proper view of what they would look like in reality. This was initially made possible by electromagnetic sensors, but has converted to [[infrared]] cameras.

The user wears 3D glasses inside the CAVE to see imagery generated by the CAVE. People using the CAVE can see objects apparently floating in the air, and can walk around them, getting a proper view of what they would look like in reality. This was initially made possible by electromagnetic sensors, but has converted to [[infrared]] cameras.

The frame of early CAVEs had to be built from non-magnetic materials such as wood to minimize interference with the [[electromagnetic tracking]] system; the change to infrared tracking has removed that limitation. A CAVE user's movements are tracked by the sensors typically attached to the 3D glasses and the video continually adjusts to retain the viewers perspective. Computers control both this aspect of the CAVE and the audio aspect.  There are typically multiple speakers placed at multiple angles in the CAVE, providing [[3D sound]] to complement the [[3D video]].{{citation needed|date=August 2013}}

The frame of early CAVEs had to be built from non-magnetic materials such as wood to minimize interference with the [[electromagnetic tracking]] system; the change to infrared tracking has removed that limitation. A CAVE user's movements are tracked by the sensors typically attached to the 3D glasses and the video continually adjusts to retain the viewers perspective. Computers control both this aspect of the CAVE and the audio aspect.  There are typically multiple speakers placed at multiple angles in the CAVE, providing [[3D sound]] to complement the [[3D video]].

==Technology==

==Technology==

A lifelike visual display is created by projectors positioned outside the CAVE and controlled by physical movements from a user inside the CAVE.  A [[motion capture]] system records the real time position of the user. [[Stereoscopic]] [[LCD shutter glasses]] convey a [[3D computer graphics|3D]] image.

A lifelike visual display is created by projectors positioned outside the CAVE and controlled by physical movements from a user inside the CAVE.  A [[motion capture]] system records the real time position of the user. [[Stereoscopic]] [[LCD shutter glasses]] convey a [[3D computer graphics|3D]] image.

The computers rapidly generate a pair of images, one for each of the user's eyes, based on the motion capture data.  The glasses are synchronized with the projectors so that each eye only sees the correct image.  Since the projectors are positioned outside the cube, mirrors are often used to reduce the distance required from the projectors to the screens.  One or more computers drive the projectors.  Clusters of desktop PCs are popular to run CAVEs, because they cost less and run faster.

The computers rapidly generate a pair of images, one for each of the user's eyes, based on the motion capture data.  The glasses are synchronized with the projectors so that each eye only sees the correct image.  Since the projectors are positioned outside the cube, mirrors are often used to reduce the distance required from the projectors to the screens.  One or more computers drive the projectors.  Clusters of desktop PCs can run CAVEs. They are faster and less expensive.

Software and libraries designed specifically for CAVE applications are available.  There are several techniques for rendering the scene. There were 3 popular [[scene graph]]s in use: [[OpenSG]], [[OpenSceneGraph]], and [[OpenGL Performer]].  OpenSG and OpenSceneGraph are open source; while OpenGL Performer is free, its source code is not included.

Software and libraries designed specifically for CAVE applications are available.  There are several techniques for rendering the scene. There were 3 popular [[scene graph]]s in use: [[OpenSG]], [[OpenSceneGraph]], and [[OpenGL Performer]].  OpenSG and OpenSceneGraph are open source; while OpenGL Performer is free, its source code is not included.

==Calibration==

==Calibration==

To be able to create an image that is not distorted or out of place, the displays and sensors must be calibrated. The calibration process depends on the [[motion capture]] technology being used. Optical or Inertial-acoustic systems only requires to configure the zero and the axes used by the tracking system. Calibration of electromagnetic sensors (like the ones used in the first cave) is more complex. In this case a person will put on the special glasses needed to see the images in 3D.

To be able to create an image that is not distorted or out of place, the displays and sensors must be calibrated. The calibration process depends on the [[motion capture]] technology being used. Optical or [[inertial-acoustic]] systems only requires to configure the zero and the axes used by the tracking system. Calibration of electromagnetic sensors (like the ones used in the first cave) is more complex. In this case a person will put on the special glasses needed to see the images in 3D.

The projectors then fill the CAVE with many one-inch boxes set one foot apart. The person then takes an instrument called an "ultrasonic measurement device" which has a cursor in the middle of it, and positions the device so that the cursor is visually in line with the projected box.

The projectors then fill the CAVE with many one-inch boxes set one foot apart. The person then takes an instrument called an "ultrasonic measurement device" which has a cursor in the middle of it, and positions the gadget so that the cursor is visually in line with the projected box.

This process can go on until almost 400 different blocks are measured. Each time the cursor is placed inside a block, a computer program records the location of that block and sends the location to another computer.

This process can go on until almost 400 different blocks are measured. Each time the cursor is placed inside a block, a computer program records the location of that block and sends the location to another computer.

==Uses==

==Uses==

Prototypes of parts can be created and tested, interfaces can be developed, and factory layouts can be simulated, all before spending any money on physical parts. This gives engineers a better idea of how a part will behave in the product in its entirety. CAVEs are also used more and more in the collaborative planning in construction sector.<ref>{{cite web|author=Nostrad |url=http://www.slideshare.net/Swecofinland/sweco-cave-20140613jjau |title=Collaborative Planning with Sweco Cave: State-of-the-art in Design and Design Management |publisher=Slideshare.net |date=2014-06-13 |accessdate=2014-08-04}}</ref> Researchers can use CAVE system to conduct their research topic in a more accessible and effective method. For example, CAVEs was applied on the investigation of training subjects on landing an F-16 aircraft.<ref>{{Cite journal|last1=Repperger|first1=D. W.|last2=Gilkey|first2=R. H.|last3=Green|first3=R.|last4=Lafleur|first4=T.|last5=Haas|first5=M. W.|date=2003|title=Effects of Haptic Feedback and Turbulence on Landing Performance Using an Immersive Cave Automatic Virtual Environment (CAVE)|journal=Perceptual and Motor Skills|volume=97|issue=3|pages=820–832|doi=10.2466/pms.2003.97.3.820|pmid=14738347|s2cid=41324691 }}</ref>

Prototypes of parts can be created and tested, interfaces can be developed, and factory layouts can be simulated, all before spending any money on physical parts. This gives engineers a better idea of how a part will behave in the product in its entirety. CAVEs are also used more and more in the collaborative planning in construction sector.<ref>{{cite web|author=Nostrad |url=http://www.slideshare.net/Swecofinland/sweco-cave-20140613jjau |title=Collaborative Planning with Sweco Cave: State-of-the-art in Design and Design Management |publisher=Slideshare.net |date=2014-06-13 |accessdate=2014-08-04}}</ref> Researchers can use CAVE system to conduct their research topic in a more accessible and effective method. For example, CAVEs was applied on the investigation of training subjects on landing an F-16 aircraft.<ref>{{Cite journal|last1=Repperger|first1=D. W.|last2=Gilkey|first2=R. H.|last3=Green|first3=R.|last4=Lafleur|first4=T.|last5=Haas|first5=M. W.|date=2003|title=Effects of Haptic Feedback and Turbulence on Landing Performance Using an Immersive Cave Automatic Virtual Environment (CAVE)|journal=Perceptual and Motor Skills|volume=97|issue=3|pages=820–832|doi=10.2466/pms.2003.97.3.820|pmid=14738347|s2cid=41324691 }}</ref>

The EVL team at UIC released the CAVE2 in October 2012.<ref>{{cite web|author=EVL|url=http://www.evl.uic.edu/cave2|title= CAVE2: Next-Generation Virtual-Reality and Visualization Hybrid Environment for Immersive Simulation and Information Analysis|date=2009-05-01|accessdate=2014-08-07}}</ref> It is based on LCD panels rather than projection.

The EVL team at UIC released the CAVE2 in October 2012.<ref>{{cite web|author=EVL|url=http://www.evl.uic.edu/cave2|title= CAVE2: Next-Generation Virtual-Reality and Visualization Hybrid Environment for Immersive Simulation and Information Analysis|date=2009-05-01|accessdate=2014-08-07}}</ref> It is based on LCD panels.

 

==References==

==References==