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Introduction

There are three commonly used methods of representing an astronomical celestial image in a FITS format file:

The first method is the most commonly used, but the other 2 ways of representing an image are useful in certain applications. In high energy astrophysics, for example, the images are often very sparse, so it is more efficient to simple list the pixel location in the image of all the detected photons rather than store the full 2-D image.

In addition to storing the image data values themselves in the FITS file, one also needs to record an associated set of parameters which describe how the image data are projected onto the celestial sphere. The paper entitled ``Representations of Celestial Coordinates in FITS'' (here after referred to as RCCF) by E. W. Greisen and M. Calabretta dated October 5, 1995, defines a convention for a set of FITS keywords that describe the celestial coordinate system for the first type of image representation, namely, for a FITS primary array or IMAGE extension. The purpose of this present paper is to define a convention for the analogous set of keywords that should be used when the image is represented in one of the other 2 methods.


next up previous FITS Documents
Next: Types of image representations Up: No Title Previous: No Title