![]() The hardware and software technologies for stereoscopic 3-D visualization on computer screens have been significantly perfected and made more affordable over the past decade, as we will briefly see in this paper. When viewing imagery and vector data using stereoscopic 3-D vision the interrelationships between features and the real world become clearer, photo interpretation becomes more accurate and complete, and spatial accuracy is increased. Stereopsis is the physiological process in visual perception in which the human brain synthesizes and fuses the two slightly different projections of the world onto the retinae of the two eyes to create this sensation of depth. Most humans have the capability to perceive and measure depth with two eyes using binocular (stereo) vision. In stereoscopic 3-D rendering, there is a much truer perception of depth (the 'third dimension'), of different scene planes, and of object relief, as each eye is actually presented with a slightly different image of the same scene, while in conventional (pseudo or "flat") 3-D presentations, depth can only be approximately simulated at best, as only one image is offered to both eyes. Stereoscopic 3-D (three-dimensional) visualization is often confused with the conventional display of 3-D objects and scenes on a computer screen or other media. A practical account is also given of the experience of the USGS BRD UMESC (United States Geological Survey's Biological Resources Division, Upper Midwest Environmental Sciences Center) in setting up a low-cost, full-colour stereoscopic 3-D system. This paper presents a brief review of a number of stereoscopic 3-D hardware and software solutions for creating and displaying online maps and virtual globes (such as Google Earth) in "true 3D", with costs ranging from almost free to multi-thousand pounds sterling. The goal of stereoscopic 3-D displays is to project a slightly different image into each eye to achieve a much truer and realistic perception of depth, of different scene planes, and of object relief. Depth in such cases can only be approximately inferred from visual clues in the image, such as perspective, as only one image is offered to both eyes. However, when a person views a conventional 2-D (two-dimensional) image representation of a 3-D (three-dimensional) scene on a conventional computer screen, each eye receives essentially the same information. The slight difference between the right and left images allows the brain to properly perceive the 'third dimension' or depth in a scene (stereopsis). Because our pupils are about 6.5 cm apart, each eye views a scene from a different angle and sends a unique image to the visual cortex, which then merges the images from both eyes into a single picture.
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