Google has described a projection technique called Equi-Angular Cubemaps that can improve VR/360° video quality:
The image quality issue that plagues spherical video sources is a perspective problem. A traditional 2D video records a predetermined frame and is played back on a display of the same shape and perspective. VR/360-degree video doesn't offer that luxury. Although you can choose which perspective you wish to see, your view is always a fixed resolution and shape, no matter where you look. The image is technically flat, which means the source feed must be warped to fit a flat plane. The process is comparable to what cartographers go through when trying to map the globe to a flat surface. In order to fit the spherical earth map onto a flat image, the perspective must be altered.
[...] Google's Daydream and YouTube engineers came up with a new projection technique called Equi-Angular Cubemaps (EAC) that offers less disruptive image degradation. EAC keeps the pixel count even between cubemap samples, which produces balanced image quality across the board. [...] Google is already putting Equi-Angular Cubemap projection to work. Spherical video playback from YouTube with EAC support is now available on Android devices, and Google said support for iOS and desktop is coming soon. If you want to know more about EAC, Google's blog offers a deeper explanation of the technology, and the YouTube Engineering and Developers blog has additional details.
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Also at Google's Research Blog.
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(Score: 0) by Anonymous Coward on Saturday March 18 2017, @07:45PM (1 child)
NASA already has a standard for this, called HEALPix: http://healpix.jpl.nasa.gov/ [nasa.gov] .
How is Google's EAC different from NASA's standard?
(Score: 1, Informative) by Anonymous Coward on Saturday March 18 2017, @08:38PM
Well, EAC is based on a single projection applied to each of the six faces of a cube, just like cubemaps -- the only difference is that this uses a different projection. Like ordinary cubemaps, it's very good at not wasting pixels in raster texture buffers (each face is a true square, and the six squares can be packed neatly in a rectangle); it approximates equal area much better than a regular cubemap, but it's not a true equal-area projection.
HEALPix uses one (Lambert) projection for the equatorial region, and another (Collignon) for the polar regions. This is a true equal area projection, and has uniform representation of latitude, but at the cost of huge unused areas in both polar regions; roughly 30% of the bounding box is unused.
So they really don't have much in common.