kirxkirx
commented
4 years ago The rotation angle reported in 'vast_image_details.log' is the relative rotation of the current frame with respect to the reference frame (not the North direction - VaST knows nothing about it when matching images based on pixel coordinates of stars). The rotation angle reported in 'vast_image_details.log' for the reference frame is always 'rotation= 0.000'. If the reported rotation is even slightly different - this image is not what VaST used as the reference frame (same filename in a different directory?).
By default, VaST is using the first image it finds as the reference. This might be the first image specified on the command line, in the 'vast_list_of_input_images_with_time_corrections.txt' file or the first file in a directory (if a directory containing images was specified on the command line). This usually works fine as the practice shows that the good reference image foe VaST is the most typical image for the given data set rather than the best one (in terms of depth or seeing). The trick with specifying the directory rather than the list of files on the command line is that the files are written in the directory in quasi-random rather than in the alphabetical order (they are often displayed in the alphabetical order by 'ls' or file manager). So if you copy the same directory to another computer the file order in the directory (as it appears to VaST) might be different and VaST might choose a different reference image! The best way to avoid this is to explicitly specify the reference image as the first one on the command line, followed by the directory containing all the images.
VaST has also the option to try to automatically select a good reference image when started with the '--autoselectrefimage' option, but the selection algorithm is rudimentary and I was not sufficiently happy with the result to use this parameter in practice. Definitely there is a room for improvement here!
mrosseel
I take the reference frame chosen by VaST in 'vast_summary.log' and perform plate solving using astrometry.net.
Up till now, when I overlay this reference frame with the wcs transformed x/y coordinates on the ref frame (given by VaST), they match perfectly.
Now I have the case where the rotation of the reference frame chosen by VaST is 180.3 degrees as found in 'vast_image_details.log'.
==> there is no more a match between wcs transformed xy coordinates and the reference frame. Not when I plate-solve the original ref frame, nor when I rotate the reference frame by 180.3 degrees and plate solve that. Is there some translation I need to take into account or something else I misunderstood?
PS: we found our first 17 new variable stars, I'll send you the link by mail