The PanSTARRS images are interpolated onto a regular grid of images that cover the sky. The grid consists of large 4°x4° projection cells that are centered on lines of constant declination spaced 4 degrees apart. For convenience of access, each projection cell is divided into a 10x10 grid of skycells, each 0.4°x0.4°. The skycells for a given projection cell share a seamless world coordinate system with the same tangent projection, so they can be easily pasted together to produce larger images. The pixel size is 0.25 arcsec.
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The RINGS.V3 Tessellation
The PS1 image layout for the 3PI survey is called the RINGS.V3 tessellation. It was defined by Tamas Budavari to meet the goals of defining a regular image pattern with nearly square cells that covers the sky while minimizing redundant image overlap. The sizes of the large projection cells are approximately constant over the sky.
The projection cell centers are located on lines of constant declination spaced 4° apart. At a given declination, the pointing centers are equally spaced in right ascension around the sky, with the number of RA points changing to account for the convergence of RA lines in the spherical sky. The pattern is defined to cover the entire sky from δ = −90° to +90°. There are 46 declination bands numbered starting at 0 for an image at δ = −90°, 1 for a row of 9 images centered at δ = −86°, 2 at δ = −82°, and so on; the images on rows 22 and 23 are at δ = −2° and +2°, and rows 44 and 45 are at δ = +86° and +90° respectively.
Since the PS1 survey covers the sky only for δ > −30°, not all projection cells are used for PS1 images.
Table of values
Skycells
Attach Tamas's PDF file
Image showing all projection cells
Image showing region near pole
Image showing skycells with overlap
Discuss skycell overlap and projection cell overlap
Note that this tessellation applies to the PS1 3PI survey. For the Medium Deep Surveys (which do not yet have image products
