Published in Astronomy & Astrophysics 395, 1059, 2002.
astro-ph/0207407.

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REPRESENTATIONS OF WORLD COORDINATES IN FITS

E. W. Greisen (1) - M. R. Calabretta (2)


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


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. Methods: data analysis - Techniques: image processing - Astronomical data bases: miscellaneous


Table of Contents

INTRODUCTION

BASIC CONCEPTS
Coordinate definition and computation
Basic formalism
Linear transformation matrix
Usage comments
Additional points
Coordinate dimensionality
Keyword value units
Keyword value defaults
Alternate axis descriptions
Uncertainties in the coordinates

ALTERNATE FITS IMAGE REPRESENTATIONS: PIXEL LIST AND VECTOR COLUMN ELEMENTS
Multi-dimensional vector in a binary table
Tabulated list of pixels
Keyword naming convention
Multiple images and the "Greenbank Convention"
Coordinate system cross-references

SPECIFICATION OF UNITS

ADDITIONAL MATTERS
Image display conventions
Units in comment fields
Tables
Conventional coordinate types

HEADER CONSTRUCTION EXAMPLE

SUMMARY

REFERENCES

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