Identified Star Coordinates?

[Abdullah Qureshi]

Hello,
I was wondering a few things if someone could help me out.

1) I was wondering if the .xyls file and the .rdls file are the confirmed star coordinates (pixel and ra, dec). or is it an initial guess?
I am trying to use the star coordinates, so I was wondering if the program knows which coordinates are stars or noise based on the match. (matched stars would be confirmed stars and not noise, then projecting across the image to find other matched stars?)

2) I am trying to overlay the .xyls coordinates onto my image. but when doing so there is a shift or scaling issue? 
is there a reference point I need to be aware of?
the overlay (red circles) don't over lay the image. 
I am doing this to also find the brightness of each star.

3) I was wondering how the astromety.net calculates the wcs file
what formulas does it use to calculate the rotation matrix?

Many Thanks,
Abdullah

[Dustin Lang]

Hi,

xyls are stars detected in your image (without looking at the sky)

rdls are stars from the reference catalog (known stars) in the sky area of your image.

The corr file gives stars that we think match.

The xyls stars are 1-indexed - 1.0 is the center of the first pixel.  Note that there may be a vertical flip, depending on whether you think y=1 is the top pixel or the bottom pixel.

A rough estimate of the brightness of each star is in the xyls file (axy.fits file on the web site) in the FLUX column.

Here's the WCS fitting routine

https://github.com/dstndstn/astrometry.net/blob/main/util/fit-wcs.c#L672

cheers,

dustin

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