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. Software and libraries designed specifically for CAVE applications are available. There are several techniques for rendering the scene. There are 3 popular scene graphs in use today: OpenSG, OpenSceneGraph, and OpenGL Performer. OpenSG and OpenSceneGraph are open source; while OpenGL Performer is free, its source code is not included. Calibration To be able to create an image that will not be 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. 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. If the points are calibrated accurately, there should be no distortion in the images that are projected in the CAVE. This also allows the CAVE to correctly identify where the user is located and can precisely track their movements, allowing the projectors to display images based on where the person is inside the CAVE. Applications The concept of the original CAVE has been reapplied and is currently being used in a variety of fields. Many universities own CAVE systems. CAVEs have many uses. Many engineering companies use CAVEs to enhance product development. 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