Software to align VLBI images based on 2D cross-correlation. Copyright (C) 2017 Tuomas Savolainen
usage: FITSalign.pl [-aco] image1 image2 [x1 y1 x2 y2 xtemp1 ytemp1 xtemp2 ytemp2]
The purpose of this program is to align two FITS images by normalized 2D cross-correlation. The input images need to have the same pixel size and their PSFs (or restoring beams) should be identical.
The program first plots the input images and asks the user to select an appropriate area for the subsequent analysis. Then the user is prompted to select a feature in the image to be matched. In the case of aligning radio images of AGN jets taken at different frequencies, it is important to select a feature that is optically thin and does not show strong spectral gradients.
The program calculates a normalized cross-correlation between the first image and the selected feature of the second image using a fast method described by J.P. Lewis (1995). The correlation plot is shown along with useful information about the shift between the input images (calculated from the maximum of the correlation plot).
The program also calculates two spectral index images: one with the calculated shift applied and one without. Check the results! The program gives a warning if the feature selected for matching turns out to contain optically thick parts. Finally, it is possible to write out the spectral index image (with the shift applied) as well as the correlation plot as FITS files.
Switches:
-o=outfile If outfile is given, the output is written to outfile.out
and the spectral index image to outfile.fits.
-c=icut Parameters icut and is the cut-off level used in calculating
spectral index maps. They are optional: if not specified by the user,
a value of 0.001 Jy/beam is used.
-a Automatic mode: The user still needs to provide the coordinates
of the image region and template in [x1 y1 x2 y2 xtemp1 ytemp1 xtemp2
ytemp2]. No output graphics.
NOTE THAT BAD VALUE SUPPORT IN PDL IS NEEDED TO RUN THIS PROGRAM.