How to create a accurate WCS with some simple method
Matrix wrote on May 12, 2015
Hello, everyone! Today I encounter a second question: I found the WCS and RA/DEC did not have a right correspondence in my fits file. And this cause a problem: when I want to know the target star, I move the mouse to the accurate RA/DEC (from the header), but it may not be the target star. So I want to create a accurate WCS, I heard SCAMP can do some work in this problem, but I don't know how to do it? Can anyone tell me some procedures in detail? Thanks a lot to you.
Mike Fitzpatrick wrote on May 12, 2015
The thing to remember is that there is no standard definition of the RA/DEC header keywords, and that these have no defined relation to the WCS itself. Depending on the instrument/control system, RA/DEC may refer to the (unprecessed) coordinates of an object in the field, a pointing value for the telescope, the center position of a dither field, etc. So, before deciding the WCS is wrong, you should test the readout of coords to see whether a cursor put on an object corresponds to some known object or whether there is a systematic offset, and necessarily whether the WCS ties to the RA/DEC keywords in some logical way.
The astromatic.net forums can be used to discuss SCAMP, for computing a WCS in IRAF see the "Creating a Mosaic WCS" document (http://iraf.net/irafdocs/astrom.php) for an overview, you'll need to adjust this a but for a single-frame image.
Matrix wrote on May 13, 2015
Thank you, fits. There is few difference between celestial coordinates of some known stars on the fits and celestial coordinates of these stars on the SDSS DR12 finding tool. I don't know which one I should use to create the accurate wcs. Additional, for IRAF to create right wcs, I don't know how to collect the pixel coordinates and the celestial coordinates I should choose which.
Last post on May 13, 2015