Sun, 11/07/2021 - 14:00
I use the SKYX to plate solve my images before uploading. But I know that vphot does indeed plate solve any image uploaded. Is my extra step before uploading (plate solving by the SKYX) necessary as it speeds up processing or is it redundant?
The reason I am asking is that I don't know if the SkyX codes the "solving" in the fits headers or not. I do know that the SkyX generates and extra file with each fits solved, which I assume has the results of the "solution", but those cannot be uploaded.
Thanks!
Marco
Marco,
I use The SkyX Pro also and this program does not inform the fits header after a plate solve (Image Link or Closed Loop Slew). I found this out the hard way as i generally rely upon plate solves to locate my photometry targets and neglect/disregard pointing errors(TPoint). I have it directly from Bisque that the fits header is informed by where TSX thinks (I am paraphrasing here and this is not a direct quote from Bisque) it is pointing even if the target was acquired by Closed Loop Slew and even if an Image Link was performed after the slew (I do this to calculate and record the position angle). I was advised that if my pointing is not accurate I should update this information after a slew by performing a Star Synchronization via Telescope/Startup. Either that or maintain an accurate TPoint model and 'assume' the coordinates for my target will be close enough.
I don't have very many posts on the Bisque forums so you can probably just search for my name to find this thread there.
John Downing
DJCA
I use TSX to plate solve my images and find that WCS are correctly stored in the FITS header by that program. I run a script to do it using this https://www.bisque.com/wp-content/scriptthesky/class_image_link.html class. AIJ reports the resulting images correctly plate solved. I never really checked what VPhot thinks,
If you are doing the image link through the GUI, perhaps you have to manually save the image?
SWCREATE = 'TheSkyX Version 10.5.0 Build 12503' / SBIGFITSEXT Name & version of s
CTYPE1 = 'RA---TAN' / gnomonic projection
CRPIX1 = 1535.31713626472 / pixel i-coordinate at field center
CRVAL1 = 257.272083333333 / RA at field center
CTYPE2 = 'DEC--TAN' / gnomonic projection
CRPIX2 = 1022.73557453435 / pixel j-coordinate at field center
CRVAL2 = 16.4747222222222 / Dec at field center
CD1_1 = 0.000186248482556533 / xi rotation-skew-scale matrix element
CD1_2 = 2.70616506006792E-06 / xj rotation-skew-scale matrix element
CD2_1 = -2.70518222326121E-06 / yi rotation-skew-scale matrix element
CD2_2 = 0.000186282917230562 / yj rotation-skew-scale matrix element
RADECSYS = 'FK5 ' / type of RA-Dec
EQUINOX = 2000. / epoch of mean equator & equinox
MJD-OBS = 0. / epoch of observation (TAI MJD)
WCSVER = 1. / A WCS version number
INPUTFMT = 'FITS ' / Format of file from which image was read
SWOWNER = 'Clifford Kotnik' / Licensed owner of software
I checked the header (see a comment below) and I do see the same fits headers you have, even though I use the Image Link Tool without the use of the script. So it seems that some sort of plate solving is taking place. The only way to see what VPHOT thinks would be to send up un-solved images, but I don't want to "gum up" the works.
I'll keep doing what I usually do, i.e. , plate solve in TSX and the upload.
Marco
Marco:
VPhot can plate solve your uploaded images IF you have set up your VPhot telescope settings properly (i.e., image scale), and the RA/Dec headers are present in the images.
However, it is appreciated if you pre-plate solve your images before uploading since it speeds up the VPhot queue processing.
IF appropriate WCS headers (e.g., CD1-1) have been installed by your own plate-solving software, VPhot will see this and skip its own plate-solve of your images. Thus, the queue moves faster.
However, John mentioned below that TSX does not insert appropriate WCS fits headers, so that VPhot understands that plate solving has already been done.
IOW, since that is reportedly not the case with TSX, your images are being plate-solved by VPhot during upload. I assume you are able to process your images successfully in VPhot? If this is true, you are wasting your time to plate solve with TSX. I use PinPoint to plate solve my own images before upload.
Does this answer your questions?
Ken
Yes, it does. The…
Hi Ken:
Yes, it does. The SKYX (Image link tool) is very fast at plate solving but if the file is not modified with the new information, it is pointless. Vphot has no trouble plate solving my images, but clearly that makes things go slower.
Since I use PixInsight to manage my calibration step, and I know that Pixinsight can plate solve as well, I'll see if I can implement that further step.
Thank you all!
Marco
HI,
I found that after running ImageSolver on a FITS file with PixInsight, and then uploading to VPhot, the file fails to appear in the image list.
But, when adding a missing "EQUINOX= 2000.0" line in the FITS header it all worked. (Thanks George Silvis)
See "VPhot not loading Image" thread.
Good luck!
…
Well, I did an experiment.
I took an unsolved image and read the fits header. There are 54 lines of headers. I plate solved with SKYX the same image and read the fit header. Now there are more lines of header (85 lines).
OJCTRA and OBJCTDEC headers are changed (numbers are different and now there is a line labeled WCSVER and the value is 1.
It seems that plate solving in the SKYX does indeed modify the header. I am not sure if that amounts to an actual "plate solution" but I suspect that now the coordinates of the center of the image are "exact" (closer to the correct value, anyway), and thus making VPHOT's job easier.
I think the best way to answer these questions is to go to the source, the people who wrote the code. This is a direct copy of a reply from Software Bisque to my question regarding why the OBJCTRA & OBJCTDEC were incorrect even though I had used CLS and Image Linked (plate solved) the photo:
"The RA & Dec coordinates indicated by the OBJCTRA & OBJCTDEC FITS keywords are based on where the mount “thinks” that it is pointing (as also seen on the star chart). If the mount is correct then you’re golden. When you CLS, the mount’s position will be adjusted based on the Image Link calculated difference to the desired target, but it does not resynchronize the mounts position against the star chart. You can see if this is the case when the red and yellow bulls eye symbols are not perfectly aligned after a CLS – the mount’s position and the target location on the chart are different even though you know that the mount *is* actually on the target in the real world.
Now, if you subsequently Image Link the photo (presumably after the CLS), the solved coordinates for the picture are stored within the WCS-related keywords located further down in the FITS header. TheSkyX Pro does not, however, re-write the existing OBJCTRA & OBJCTDEC keywords to match the Image Link solution."
It seems to me there are two different things here that cause the confusion.
Plate solving to me means WCS. Other FITS header keywords describing the object that is the subject of the image are just descriptive information. WCS describes where the image is centered in RA and DEC as well as the plate scale and rotation along with some nonlinear adjustments. The object's (subject's) RA and DEC may or may not be located at the center of the image and hence the same as the WCS center. I often offset the object from the center to get a good guide star.
If you want a software routine (AIJ, VPhot, etc.) to be able associate a pixel in the image with an RA and DEC (or vice versa), you want the WCS.
I do agree TSX is not good about putting the RA/DEC of the object being observed (subject) into the FITS head and I do that as a separate step myself. However, to me that is a separate thing from the WCS which is what I think of as plate solving.
Perhaps we are not being descriptive enough in our discussion.
Cliff