Representing Celestial Coordinate Systems - 4

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• Regular arrangement of image data values offers the possibility of defining rules for computing the coordinates of each datum.



• Image array data are addressed via integral array indices - storage coordinates.



• Array indices are generalized to floating-point pixel coordinates.



• This generalization is based on the interpolability of adjacent image data values.



• If the data values are considered to be delta functions, then when displayed as finite-sized pixels, it makes most sense to assign integral pixel coordinates to the centre of the pixel.



• Henceforth, we consider only two image axes, pixel coordinates (I, J).



• Additional FITS keywords:   none.