[ PROJECTION ] posted July 10, 2008, revised October 29, 2011

"Projection" is the way to map a three-dimensional coordinate onto a two-dimensional plane, which is one of the key techniques to view a real 3D image on a 2D presentation panel such as the PC screen. Now let's take a brief look at several projection methods commonly used in the field of cartography, crystallography, geology, astronomy, architectonic, optics and photography including panoramic image generation.

We hope this tutorial helps understand how the concept of projection is relevant to shooting, stitching and showing panoramic or omini-directional photographs and motion pictures.

All the way from shooting or capturing panorama images or video clips to preprocessing, and finally viewing them is about a series of coordinate-conversion or projection process, which is the way to map a three-dimensional coordinate onto a two-dimensional plane, and is one of the key techniques to depict and duplicate a real 3-dimensional on a 2-dimiensional plane whether it is a presentation panel such as the PC screen or a 2-dimiansional addressable memory plane. Let’s take the latest and typical approach to shoot and view a still panorama as an example, where you fist take multiple shots covering the intended range or area of the space directions. Taking a photograph using an optical device such as a camera whether it uses silver film, light-sensitive tube, photo cell, or a semiconductor sensor including CCD or FET, is the first step to use the mechanism of projection. Emulating how our eyes work to look and see surrounding objects, the camera gathers incoming lights to project them onto the light sensitive panel. The type of projection such as rectilinear, orthogonal, equidistance or equisolidangle depends on the type of light collection media; the optical lens.

Modern technology has delivered on an ideal method to encode, store, compress, carry, transform, retrieve, decompress, decode and present the projected image, by means of a variety of electrical and digital hardware and software. In the typical way of creating a panoramic photograph again, the second process might be to put together or stitch those multiple images into a meaningful type of image such as the one so-called “equirectangular”. In this process again, the concept of projection is leveraged to have all those images to conform themselves into a continuous, seamless, and spectacular one. Typical stitching software internally performs rectilinear-to-equirectangular coordinate transformation to generate the final outcome. While the equirectangular type of image for example might be in a sense cool enough to see an extra wide field of view at hand, we, human being, still have a desire to exactly recreate the real viewing experience as if we stand on the point where those images were captured. Small software called panorama viewer or panorama player including RFP player (Ryubin's Flash Panorama player) , regardless of the underlying technology, has the role to meet this demand of recreating, duplicating or emulating the real experience via a virtual manner. In this process of virtually presenting the surrounding image, again, the technique of projection is used. In the typical case, a panorama player uses equirectangular-to-rectilinear coordinate transformation to recreate the real view meeting the demand of our natural sense of vision or visual sense.
Therefore, at least three steps of projection process are performed all the way from shooting to presenting a panorama image.

In addition to such natural sense of sight, people have another desire to view surroundings in an unrealistic and distorted but immersive and seamless manner or to dynamically look at scenery as wide as possible at a glance. Part of the playmodes implemented in the RFP player including sphere, sphere8, spherevideo, fisheye, dualfisheye, verticalfisheye, verticalfisheyevideo, doughnut, doughnutvideo are able to fulfill that desire as they provide extra viewing experiences we call “Orthogonal mode” and “Stereographic mode” on top of the usual viewing experience we call “Normal mode”.

Place your mouse pointer over the following picture to show a frame/grid view of each projection.