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.