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Warps are the result of resampling and realigning the camera images onto regular areas (called skycells) on the sky (basically aligned N-S, E-W). How this is done depends on the particular tessellation. Different surveys may have different tessellations. into the PS1 Sky Tessellation, a set of common pixel-grid images with simple projections from the sky. Warps are astrometrically and photometrically calibrated.
Once astrometric and photometric calibrations have been performed, images are geometrically transformed into the PS1 Sky Tessellation, a set of common pixel-grid images with simple projections from the sky. These images, called warps, can then be used in subsequent stacking and difference image analysis without concern about the astrometric transformation of an exposure. This processing is called ‘warping’; the warp analysis stage is run on all exposures before they are processed further. For details on the warping algorithm, see Waters et al paper.
A warp will generally consist of several different OTAs, therefore there are gaps between the OTAs, as well as the smaller gaps between the cells . Warps are astrometrically and photometrically calibrated.
(see example image to the right). The output products from the Warp stage consist of the skycell images containing the signal, the variance, and the mask information. These images have been shipped to STScI and will be available in DR2.
Example of a single warp (left) and stack (right) of a galaxy at Ra=23:41:52 and Dec=-08:38:54.05