I often have the case that Siril cannot detach a plate, although the correct RA and DEC are entered in the Fits header (ZWO ASI).
I found the reason:
Two coordinates are entered in the ZWO ASI Fits header
RA = 312.993 / Object Right Ascension in degrees
DEC = 31.9068 / Object Declination in degrees
…
CTYPE1 = ‘RA—TAN-SIP’ / TAN (gnomic) projection + SIP distortions
CTYPE2 = ‘DEC–TAN-SIP’ / TAN (gnomic) projection + SIP distortions
CRVAL1 = 312.121179008 / RA of reference point
CRVAL2 = 33.7346625176 / DEC of reference point
CRPIX1 = 223.516437531 / X reference pixel
CRPIX2 = 420.223754883 / Y reference pixel
The coordinates in the image center are these (identical to the solution of nova.astrometry.net)
RA 312.993 / DEC 31.9068
Unfortunately, Siril uses coordinates CRVAL1/CRVAL2 and therefore does not find a plate solution, especially for wide-field images
// image_format_fits.c
fits_read_key(fit->fptr, TDOUBLE, “CRVAL1”, &(fit->wcsdata.crval[0]), NULL, &status);
fits_read_key(fit->fptr, TDOUBLE, “CRVAL2”, &(fit->wcsdata.crval[1]), NULL, &status);
// full FITS Header read with Fitswork
//Camera ZWO ASI183MC 5.496x3.672 written by ZWO ASIAIR
SIMPLE = T / file does conform to FITS standard
BITPIX = 16 / number of bits per data pixel
NAXIS = 2 / number of data axes
NAXIS1 = 5496 / length of data axis 1
NAXIS2 = 3672 / length of data axis 2
EXTEND = T / FITS dataset may contain extensions
COMMENT FITS (Flexible Image Transport System) format is defined in ‘Astronomy
COMMENT and Astrophysics’, volume 376, page 359; bibcode: 2001A&A…376…359H
BZERO = 32768 / offset data range to that of unsigned short
BSCALE = 1 / default scaling factor
CREATOR = ‘ZWO ASIAIR’ / Capture software
OFFSET = 10 / camera offset
XORGSUBF= 0 / Subframe X position in binned pixels
YORGSUBF= 0 / Subframe Y position in binned pixels
FOCALLEN= 129 / Focal length of telescope in mm
EGAIN = 0.361999988555908 / Electronic gain in e-/ADU
XBINNING= 1 / Camera X Bin
YBINNING= 1 / Camera Y Bin
CCDXBIN = 1 / Camera X Bin
CCDYBIN = 1 / Camera Y Bin
XPIXSZ = 2.40000009536743 / pixel size in microns (with binning)
YPIXSZ = 2.40000009536743 / pixel size in microns (with binning)
IMAGETYP= 'Light ’ / Type of image
EXPOSURE= 60. / Exposure time in seconds
EXPTIME = 60. / Exposure time in seconds
CCD-TEMP= 19.2999992370605 / sensor temperature in C
RA = 312.993 / Object Right Ascension in degrees
DEC = 31.9068 / Object Declination in degrees
DATE-OBS= ‘2021-06-26T23:08:59.635’ / Image created time
INSTRUME= ‘ZWO ASI183MC’ / Camera model
BAYERPAT= 'RGGB ’ / Bayer pattern
GAIN = 200 / Gain Value
TELESCOP= ‘EQMod Mount’ / Telescope name
CTYPE1 = ‘RA—TAN-SIP’ / TAN (gnomic) projection + SIP distortions
CTYPE2 = ‘DEC–TAN-SIP’ / TAN (gnomic) projection + SIP distortions
CRVAL1 = 312.121179008 / RA of reference point
CRVAL2 = 33.7346625176 / DEC of reference point
CRPIX1 = 223.516437531 / X reference pixel
CRPIX2 = 420.223754883 / Y reference pixel
CD1_1 = 0.000807569282086 / Transformation matrix
CD1_2 = 0.00418054387455 / no comment
CD2_1 = -0.00417444284354 / no comment
CD2_2 = 0.000809792917224 / no comment
A_ORDER = 2. / Polynomial order, axis 1
B_ORDER = 2. / Polynomial order, axis 2
AP_ORDER= 2. / Inv polynomial order, axis 1
BP_ORDER= 2. / Inv polynomial order, axis 2
A_0_0 = 0. / no comment
A_0_1 = 0. / no comment
A_0_2 = -3.25240106779E-07 / no comment
A_1_0 = 0. / no comment
A_1_1 = 6.0794245259E-07 / no comment
A_2_0 = 2.61332074741E-06 / no comment
B_0_0 = 0. / no comment
B_0_1 = 0. / no comment
B_0_2 = 1.11192069938E-06 / no comment
B_1_0 = 0. / no comment
B_1_1 = 2.39138889379E-06 / no comment
B_2_0 = -9.69984828717E-08 / no comment
AP_0_0 = -0.000456247442657 / no comment
AP_0_1 = -3.32926651844E-07 / no comment
AP_0_2 = 3.24113136033E-07 / no comment
AP_1_0 = -4.99420259789E-06 / no comment
AP_1_1 = -6.0232632373E-07 / no comment
AP_2_0 = -2.59430009291E-06 / no comment
BP_0_0 = -0.000279764680655 / no comment
BP_0_1 = -6.52274365771E-07 / no comment
BP_0_2 = -1.10734330604E-06 / no comment
BP_1_0 = 5.37876957752E-07 / no comment
BP_1_1 = -2.37993967797E-06 / no comment
BP_2_0 = 9.64151604334E-08 / no comment
IMAGEW = 1372. / Image width, in pixels.
IMAGEH = 916. / Image height, in pixels.
END
