Three dimensional, or 3D, projection, which is often called 3D projection mapping, is the transference of three-dimensional data onto a two-dimensional plane. Scientists, engineers, and designers often make use of this type of mapping system when making computer or pen and paper models of three-dimensional objects. Objects may be drawn to scale or with perspective, but both qualities cannot be kept intact after translating three dimensional coordinates into two dimensions. Though 3D projection usually refers to the modeling itself, it can also refer to the projection of images that appear to be in three dimensions, such as those seen in 3D films.
By its nature, the act of transferring three dimensional information onto a two dimensional plane means that something must be lost. There are two main ways to use 3D projection, and each has its own positive and negative qualities. One way to project a three dimensional image onto a two dimensional surface is by using perspective. Perspective makes an image look to the eye as if it were three dimensional, though the sizes of the parts of that object, if measured, would not be proportionally correct. The other way to use two dimensions to represent three is to use a system called orthographic projection. In this system, the measurements are accurate but the object will not look like it has depth.
There are a number of uses for 3D projection. Engineering design and drafting both make use of three dimensional coordinate systems in the design of buildings and structures. Computer graphics also use 3D projection when modeling a three dimensional object or environment in the two dimensional space of a computer screen. Science and mathematics may also use this type of projection when modeling or graphing various natural phenomena and equations.
3D projection can also refer to the projection of two dimensional images onto a screen in such a way that they appear to the viewer to exist in three dimensions. The technology to make a two dimensional image appear to have depth has been available since the 1920s, and though there have been many improvements, the basic principles are the same. Instead of one image, two images that overlap slightly are placed on a screen at the same time. When a person is wearing special glasses, either color filters or polarized filters, each eye is only able to see one of these images, and the brain translates the information received by each eye into one three dimensional image.