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scanlineA subdivision of a strip. Each strip is covered by 6 "scanlines". Scanlines are defined in great circle coordinates. The great circle coordinate system is different for each strip, and is defined by setting the equator of the coordinate system to be the center line of constant eta for the stripe to which the strip belongs. A scanline is then bounded on the top and bottom by lines of constant nu, with no east or west boundaries. Scanlines touch but don't overlap, and thus are a unique mapping on the sky for that stripe only. Scanlines for different stripes DO overlap. This is because the scanlines come from the camera columns, or camcols, which have a fixed physical width, while the spherical coordinates converge at the poles. Note: At times, the term scanline has been used interchangeably (and improperly) with camcol.