Representing Celestial Coordinate Systems - 3

FITS square pixel grid (15x15), in blue

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  • FITS (Flexible Image Transport System) is the IAU standard for data interchange in astronomy.

  • Data values in a FITS image array occupy a regular N-dimensional lattice structure.

  • Ordered so that the first axis varies fastest (FORTRAN order).

  • Best thought of as an array of delta sampling functions on a square grid.

  • For display purposes

    • Delta functions are represented as finite-sized, square pixels (not rectangular or hexagonal).

    • By convention, the first pixel is at lower-left, increasing to the right, then upwards.

  • FITS keywords:   NAXIS, NAXISj.