IRAF Tools for ESO imaging survey data
Version : 4
Author(s) : Richard Hook in conjunction with the EIS team
License : ESO
Website : http://iraf.noao.edu
Installs from Open Source Astronomy for Linux cd 2
Disk space required for installation is 1.63 Mb
This package requires prior installation of iraf
This version is somewhat specific to the ESO Imaging Survey (EIS) and the following public surveys and may not be suitable for other data.
When coadding EIS images suitable scripts are usually prepared using the "parapredriz" task and "drizzle" is not run directly. It is recommended that this route be followed.
Note that later versions have been optimised for maximum speed by using a constant kernel - a square on the output grid, aligned with the pixels. This makes the process faster with a minimal loss of quality.
Drizzling takes the input pixel grid and associates with each pixel a square region (a drop) whose size can vary between that of the original input pixel (pixfrac = 1.) down to a point (pixfrac=0). With uniform, equal weight images pixfrac=1 is equivalent to "shift-and-add". If the shifts and pixfrac are arranged so only one input pixel is drizzled onto an output pixel, the method is equivalent to interlacing. For EIS, where the data is well-sampled in all but the most exceptionally good seeing, a value of pixfrac=1.0 is used.