# Artificial PSF format

This document describes the format of a point spread function (PSF) FITS file intended for simulation in Artificial sky tool (manual).

## Structure

PSF is specified by a FITS file having one single primary image extension. The image data represent intensities in projected coordinates.

## PSF

PSF is a two-dimensional array of real values. PSF is recommended to be normalised; the total intensity under the surface can be equal to one, which helps to keep the photometry information.

The extension should have included parameter ZOOM which maps PSF on a simulated image.

Processing follows the way:

1. PSF centre is shifted to the centre of a star,
2. PSF is pixelised. Final dimensions are in width: NAXIS1/ZOOM, and in height: NAXIS2/ZOOM,
3. than PSF is directly copied on the right place of the simulated frame.

### Limitations

There are those limitations:

- Data array should cover a square, eg. NAXIS=2, NAXIS1=NAXIS2.
- ZOOM should by an integer number.

## See Also

Artificial sky tool, manual.

artpsf.f08 does generate the template artpsf.lst of PSF file; run `munipack fits --restore artpsf.lst` to make FITS itself.