Spherical panorama
A spherical panorama or spherical panorama is a panorama image in which all angles are reproduced that are visible from one point of view. Such photographs show an image angle of 360 ° in width and 180 ° in height. So they cover the entire surface of a sphere , in the center of which is the point of view of the recording.
Spherical panoramas differed from ultra-wide-angle or fisheye images, which i. d. Can usually only show image angles of less than 180 °, as well as cylindrical panoramas , which (similar to the inner wall of a barrel) can show 360 ° in the horizontal but never zenith (view up) and nadir (view down).
Types of projection and playback technology
Since spherical panoramas normally depict an angle of view that is not normally perceptible at the same time, you have to make do with their representation on two-dimensional output media (and their storage in raster graphics ) with different types of projection or an interactive representation of sections.
Of the different types of projection that enable the two-dimensional image of a full spherical surface, the rectangular projection (right-angled projection) is the most widespread for storage and imaging of spherical panoramas. It depicts the 360 ° all-round view in the horizontal and 180 ° in the vertical in a rectangle with an aspect ratio of 2: 1, with the zenith and nadir each stretched to the full width of the image corresponding to the upper or lower edge of the image and the horizon in the vertical center of the picture. As a result, the parts of the image close to the horizon are displayed relatively "normal", but the view up or down is shown strongly distorted.
Today spherical panoramas are also often output stereographically projected in order to generate so-called little planet or tube views. For mathematical reasons, however, the complete spherical panorama can never be reproduced on a finite surface in this way, since zenith or nadir are stretched into infinity with this projection method.
If you use an interactive panorama viewer to display the spherical panorama, you don't see the whole panorama at a glance, but only a section, which is then output in the planar projection familiar from normal photos. This section can be moved interactively so that you get the impression of turning around in a room and looking in all directions.
Recording technology
Different techniques are used to record spherical panoramas. A distinction can be made between two categories: sequential recordings and snapshots.
Sequential recordings
Spherical panoramas are composed of several individual images for the required angles of view, which were created one after the other and therefore show different points in time. The camera is either held and swiveled freehand - which usually leads to considerable parallax errors due to the difficult-to-control movement of the camera - or, with the help of a nodal point adapter, it is mounted in such a way that the point of intersection of the viewing angles in space remains the same across all recordings during rotation and no parallax occurs. Nodal point or VR adapters are available both in manually operated versions (see animation) and as motorized panorama heads ( panorama robots ) that automatically turn / tilt the camera in the required directions and then trigger it. Usually the camera is attached upright to the nodal point adapter.
The number of shots required to create a spherical panorama depends on the angle of view (and thus the focal length ) of the lens used. If the angle of view is 180 ° and more, it is sufficient to turn the camera once around its transverse axis. In all other cases a multi-line procedure is required in which the camera is not only panned but also tilted in height.
The image segments generated in this way are finally sorted, spatially arranged and geometrically correctly assembled with the help of stitching software on the basis of their overlaps. When calculating the images, the software tries to compensate for possible parallax or movement-related differences such as color and brightness deviations so that a seamless image is created on output.
Snapshots
For snapshots or video recordings of complete spherical panoramas, a group of cameras can be used that point in different directions and are triggered or synchronized together. Naturally, parallaxes must occur here due to the slightly different viewing angles . This cannot be technically avoided, as the nodal points of several cameras cannot be brought into congruence without these cameras being in the picture of each other. In practice, the camera modules are mounted with their backs to one another and the resulting parallaxes must be eliminated or concealed as much as possible during the subsequent stitching of the individual images.
In practice, a so-called 360 ° rig is often used for six or more cameras. Because of their small size, smaller action cams are preferred . The individual images or videos are then stitched in post-processing.
In recent years, cheaper panorama cameras for end users have increasingly come onto the market, in which the (mostly two) camera modules are already permanently installed in a compact housing. The stitching is done either directly in the camera or (if necessary with cloud support) using an associated smartphone app .
Omnidirectional cameras
Incomplete spherical panoramas can be recorded with omnidirectional cameras or with fisheye lenses with an extremely large angle of view (up to 280 °), in which only a single image is generated. The recorded image must then be mathematically rectified in order to obtain an equirectangular representation, for example.
See also
Web links
Individual evidence
- ↑ Autopano Giga - Panorama Editor - Projections - Autopano. Retrieved March 6, 2018 .
- ↑ a b 360-degree cameras in the test: Good all-round pictures are available for 200 euros , test.de from April 25, 2018, accessed on April 27, 2018
- ↑ Jan-Keno Janssen: GoPro goes 360 degrees: Six Hero 4 cameras in the rig for $ 5,000 (card fiddling included) , heise.de from April 18, 2016, accessed on April 27, 2018