Talk:Quadrilateralized spherical cube

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[Untitled][edit]

The too-technical and expert-opinion tags were added without comment or discussion, and IMO do not (or no longer) apply. Odysseus1479 (talk) 19:33, 6 November 2010 (UTC)[reply]

Projection?[edit]

This article is entirely about storage, what about the actual projection? Qartar (talk) 06:20, 22 July 2011 (UTC)[reply]

Indeed, the one part that seems about to explain the projection (conversion from bin numbers to coordinates) is a mere sentence fragment: "The conversion between bin numbers and coordinates is straightforward: if four-byte integers are used for the bin numbers the maximum practical depth, which uses 31 of the 32 bits and results in a bin size of 0.0922 square arcminutes (7.80 nanosteradians)." Can anyone work out what this is trying to say? 69.50.14.73 (talk) 16:49, 22 September 2014 (UTC)[reply]

Here, I believe, is an example projection - http://www.progonos.com/furuti/MapProj/Normal/ProjPoly/Img/cbGn-s100h-Combi.png if anyone cares to include it in the article...

I think those are gnomonic projections (one with the poles at the corners, the other face-centred), not the equal-area curvilinear projection mentioned in the article. And I don’t see a free licence on the site’s home-page; we presume images to be copyrighted unless there’s an explicit statement to the contrary, so we probably can’t use that image anyway.—Odysseus 1479 21:02, 1 April 2016 (UTC)[reply]

About this talk-section, yes, is important to add some explanations about projection... See also proj.org/QSC... But please, help edit collaboration, not reverting text, but edit enhancing the content offered by collaboration. Krauss (talk) 13:33, 19 February 2022 (UTC)[reply]

Revert not make sense, please add S2[edit]

See also the (most popular and) similar S2 Geometry system. PROJ implementation of S2 used QSC, see https://github.com/OSGeo/PROJ/pull/2749

So, if it is all ok, please add, with better English, the S2 citation. Krauss (talk) 13:28, 19 February 2022 (UTC)[reply]

Done. Is there a better reference for S2? A paper, or more independent coverage? Apocheir (talk) 21:54, 19 February 2022 (UTC)[reply]

Is it exactly equal-area?[edit]

The COBE sky cube described at https://lambda.gsfc.nasa.gov/product/cobe/skymap_info_new.html says "All COBE map data are presented in a quadrilateralized spherical projection, an approximately equal-area projection (to within a few percent) in which the celestial sphere is projected onto an inscribed cube.". ThomasTC (talk) 09:19, 13 December 2022 (UTC)[reply]

I spent some time going over the original paper, but not in enough detail to work this out rigorously. However, I think what is going on is that the Chan did not understand the technical definition of “equal-area”. He projected finite areas so that they have the same area as the spherical surface being projected, but not such that the differentials do. I think the COBE description is therefore correct. Strebe (talk) 21:46, 13 December 2022 (UTC)[reply]