Omnidirectional camera
An omnidirectional camera (also full sphere, 360 degree or VR camera) is able to take pictures from all directions in a range of 360 degrees horizontally and vertically, while panorama camera systems "only" provide a 360 degree Can map hemisphere . Despite this difference, the term “omnidirectional” is also incorrectly used for panorama camera systems. The ability to depict the whole sphere is also known as omnivision . (Omni from Latin omnis "everyone" or "whole"). The term VR camera was coined by the combination with virtual reality glasses.
construction
Various techniques can be used to create 360-degree images.
Cameras with a lens
These models are used with a fisheye lens. The lens curves the angle of the shot and thus takes up a larger radius of the selected subject. This technique cannot be used to take full 360-degree recordings as there is always a blind spot directly behind the lens.
Cameras with two lenses
360-degree cameras with two lenses are probably the most common type, as they can record a full 360-degree angle with two opposing lenses. A camera takes pictures and videos at an angle of just over 180 degrees, e.g. B. 220 degrees. These are then converted into a 360-degree object using software . Stitching errors often cause problems. This means that if the images are put together incorrectly, an unclean cut edge can arise that is difficult or impossible to remove.
Cameras with more than two lenses
Depending on the application, manufacturers use more than two camera lenses to generate the images. One of the first cameras was the “ Panono ” launch camera . This has 36 cameras, which are triggered at the highest point at the same time when the camera is thrown into the air. The more lenses are built into the camera, the more difficult it is for the software to put the individual images together. The possible stitching problems are less with a good cut.
Camera rigs
Camera rigs are usually used to attach 6 conventional action cams . GoPro made one of the first camera rigs. This is available in different versions and connects several individual cameras. These are built up like a cube. The cameras are placed in this cube and record the surroundings in all directions.
Mosaic-based cameras
If several "normal" cameras are connected in a network, one speaks of mosaic-based cameras. Each of these cameras records a small area of the environment. Then the individual images are put together like mosaic stones, so that an omnidirectional overall picture is created. The number of cameras to be used depends on the focal length of the lenses used. The smaller this is, the larger the viewing angle and the fewer cameras have to be used.
Origin of the digital 360 degree camera / VR camera
Omnidirectional cameras with mirrors (catadioptric systems)
Catadioptric image systems are currently the most promising form of omnidirectional image recording in robotics . They consisted of a combination of camera, lenses (dioptrics) and mirrors (catoptrics). A mirror was attached in front of the camera lens in such a way that it directs the light rays from all sides towards the lens. With this construction, the cameras, which were mostly installed vertically on the robots, recorded a field of view of up to 360 degrees horizontally. The types of mirrors used ranged from planar , conical , hyperbolic , spherical , elliptical to parabolic shapes.
Omnidirectional cameras are structured differently depending on the system. In their basic form, catadioptric vision systems consist of one or more cameras with a lens and an associated mirror. The name of this system is explained by the use of lenses ( dioptric optics, refractive systems) in the objective and the mirror attached to the front of the camera lens ( Katoptrik optics reflecting systems). The mirror should be designed in such a way that it reflects the light rays from as large a horizontal and vertical area as possible in the direction of the camera lens. Omnidirectional camera systems can quickly become quite large. To counteract this, there is the option of using folded omnidirectional camera systems. With this method, the path of the light is "folded", ie changed with the help of a second mirror in such a way that the size of the entire system can be reduced. The different combinations of different mirror types result in a very large variety of different systems. Either perspective or orthographic cameras are used for the recording itself.
Rotating cameras
The use of rotating cameras is another method of generating omnidirectional images using conventional cameras. Instead of many lenses in a network, only a single camera is used, which circles around a vertical axis located behind it. With this arrangement, it is also possible to produce three-dimensional images and somewhat reduce the higher cost of tessellated systems.
Cameras with special wide-angle lenses (fisheye lenses)
Another way to take panoramas is to use extreme wide-angle lenses. You orient yourself to nature, in which many animals have very large viewing areas. This is also one reason why such lenses are often referred to as " fisheye " lenses. In order to record not only panoramas but the full sphere, two of these cameras have to be attached with their backs to each other.
Omnidirectional recordings
New 360-degree cameras offer a full all-round view of the selected subject in 360 degrees both horizontally and vertically. On obsolete models of an omnidirectional camera is round with a "black spot" in the middle. This unused area in the center of the image results from the fact that the area directly above the camera cannot be seen due to the mirror construction. The picture shows the surroundings of the camera in a strongly distorted form. As a rule, the outer areas of the image show the low-lying surroundings, the inner areas the higher-lying surroundings. Depending on the camera orientation, number of mirrors and mirror shape, the omnidirectional recording can also be set up in reverse. That is, inner areas of the image are low, outer areas are high.
use
Omnidirectional cameras have their origins in military technology and, in addition to their occasional use in surveillance technology , were mainly used in mobile robots such as service robots . Since the development of 360-degree cameras has advanced and these cameras have been made usable for home use, VR cameras have been used in various areas. Little by little, older action cam models are being exchanged for a 360-degree camera. This is also due to the parallel progressing development of virtual reality glasses, which give you the feeling of reliving the experiences in the recordings. Countless possible uses are possible here.
See also
literature
- Eugene Hecht: Optik , 4th revised edition, Oldenbourg, Munich, 2005, ISBN 978-3-486-58861-3 .
Web links
- Omnidirectional vision. In: University of Pennsylvania website