Peirce quincuncial projection
Conformal map projection / From Wikipedia, the free encyclopedia
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The Peirce quincuncial projection is the conformal map projection from the sphere to an unfolded square dihedron, developed by Charles Sanders Peirce in 1879.[1] Each octant projects onto an isosceles right triangle, and these are arranged into a square. The name quincuncial refers to this arrangement: the north pole at the center and quarters of the south pole in the corners form a quincunx pattern like the pips on the five face of a traditional die. The projection has the distinctive property that it forms a seamless square tiling of the plane, conformal except at four singular points along the equator.
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Peirce_Quincuncial_with_Tissot%27s_Indicatrices_of_Distortion.svg/640px-Peirce_Quincuncial_with_Tissot%27s_Indicatrices_of_Distortion.svg.png)
Typically the projection is square and oriented such that the north pole lies at the center, but an oblique aspect in a rectangle was proposed by Émile Guyou in 1887, and a transverse aspect was proposed by Oscar Adams in 1925.
The projection has seen use in digital photography for portraying spherical panoramas.