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Tables format for imwcs

In order to use the imwcs command, like in this example:

imwcs -wvd img.cat -c ref.cat -h 100 -t 10 -q i image.fits

we need to insert the two tables img.cat, as the photometric catalog from the image (based on a rough detection), and ref.cat, as the catalog which we cross-correlate (reference catalog). But there is a specific format for these tables.

> Since the parameter “d” is used (DAOPHOT format) then the catalog img.cat is simply a 3 column text file with white-space-separated numbers on a line. The 3 columns are X and Y positions in the image (pixels) and MAG (a rough estimate of magnitudes). It is better to sort this catalog to the magnitudes. Example:

6629.311   43.663   -3.09156
69.331   2907.654   -2.75876
103.621   7751.257   -2.25899
2236.000   171.468   -2.02499
134.441   4506.971   -2.00035
...

> The reference catalog should follow the Starbase tables, with some comment lines at the beginning and 3 columns again but tab separated. The 3 columns are RA and Dec (in degrees) and magnitudes. Example:

KEY1	1
KEY2	2
KEY3	3
RA	DEC	MAG
--------------------------------------
1.2879293234e+01	-7.3433459865e+01	0.0004802001
1.3764910094e+01	-7.3720846808e+01	0.0005518933
1.4358272653e+01	-7.3178757712e+01	0.0008463736
1.2396733738e+01	-7.3172484011e+01	0.0008719206
1.2431328059e+01	-7.3145855608e+01	0.001443057
...

For more check the reference page for imwcs tool and its flags (which we do not discuss here now).

[A possible useful link is how to use sextractor to produce a table as an input to imwcs.]