Representations of world coordinates in FITS

¹ National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801-0387, USA
² Australia Telescope National Facility, PO Box 76, Epping, NSW 1710, Australia

Corresponding author: E. W. Greisen, egreisen@nrao.edu

Received: 24 July 2002
Accepted: 9 September 2002

Abstract

The initial descriptions of the FITS format provided a simplified method for describing the physical coordinate values of the image pixels, but deliberately did not specify any of the detailed conventions required to convey the complexities of actual image coordinates. Building on conventions in wide use within astronomy, this paper proposes general extensions to the original methods for describing the world coordinates of FITS data. In subsequent papers, we apply these general conventions to the methods by which spherical coordinates may be projected onto a two-dimensional plane and to frequency/wavelength/velocity coordinates.