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Some WCSes that don't work but should #212

Open keflavich opened 2 months ago

keflavich commented 2 months ago

Describe the bug These two FITS headers refuse to align with others. What is wrong with them?

Could not enable spatial matching of Bania2_downsampled_kms_try2.fits to reference image G002.5+0.0IFx_Mosaic_Mom0.fits. No valid transform was found.
Could not enable spatial matching of H2_mosaic_avg.fits to reference image G002.5+0.0IFx_Mosaic_Mom0.fits. No valid transform was found.

To Reproduce H2 header:

$ imhead H2_mosaic_avg.fits
SIMPLE  =                    T / Fits standard
BITPIX  =                  -32 / Bits per pixel
NAXIS   =                    2 / Number of axes
NAXIS1  =                 1969 / Axis length
NAXIS2  =                 1461 / Axis length
EXTEND  =                    T / File may contain extensions
ORIGIN  = 'NOAO-IRAF FITS Image Kernel July 2003' / FITS file originator
DATE    = '2024-09-08T22:04:24' / Date FITS file was generated
IRAF-TLM= '2024-09-08T22:04:24' / Time of last modification
SEQNAME = 'CDS     '
DATE-OBS= '2024-05-31T07:39:22.784000' / TAI time at start of exposure
MJD-OBS =    2460461.818634259 / Mean Julian Date of exposure
STARTCLR= '2024-05-31T07:38:50.784000' / UTC time at start of exposure
ENDRD   = '2024-05-31T07:41:57.472000' / UTC time at end of reading final frame
TIME2CLR=              0.65625 / Estimated time (sec) to clear the chip
TIME2RD =              0.67625 / Estimated time (sec) to read the chip
EXPTIME =                180.0 / Actual exposure time of CDS
IMAGETYP= 'OBJECT  '           / Type of image taken
CNPIX1  =                    1 / Lower Left X pixel pos of window (start at 1)
CNPIX2  =                    1 / Lower Left Y pixel pos of window (start at 1)
NFS     =                    8 / Number of Fowler Samples
FILTER  = 'H2-2.12 '           / The name of the current filter
FILTER1M=                    7 / The physical position of filter wheel 1
FILTER2M=                    1 / The physical position of filter wheel 2
FILTER3M=                    7 / The physical position of filter wheel 3
FPINBEAM= 'Unknown '           / Position of etalon
PRESSURE= 9.687999999999999E-007 / Instrument pressure in Torr
TEMP1VAL=               78.426 / Temperature from LN2_Container in K
TEMP2VAL=    85.10299999999999 / Temperature from Bench-FPA in K
TEMP3VAL=               100.45 / Temperature from Bench-Front in K
TEMP4VAL=    90.95399999999999 / Temperature from Bench-FP in K
OBSERVAT= 'APO'                / Per the IRAF observatory list.
TELESCOP= '3.5m'
INSTRUME= 'nicfps'             / Instrument name
LATITUDE= +3.2780361000000E+01 / Latitude of telescope base
LONGITUD= -1.0582041700000E+02 / Longitude of telescope base
TIMESYS = 'TAI'                / Time system for DATE-OBS
UTC-TAI = -37.0                / UTC = TAI + UTC_TAI(seconds)
UT1-TAI = -37.02               / UT1 = TAI + UT1_TAI(seconds)
LST     = '17:12:40.451'       / Local Apparent Sidereal time
OBJNAME = 'Bania_Clump2_e'     / Object name, per TCC ObjName
RADECSYS= 'ICRS    '           / Coordinate system, per TCC ObjSys
EQUINOX = +2.0000000000000E+03 / Equinox, per TCC ObjSys
OBJANGLE= +3.2296940000000E-02 / Angle from inst x,y to sky
RA      = '17:51:35.52'        / RA hours, extrapolated from TCC ObjNetPos
DEC     = '-25:50:52.93'       / Dec degrees, extrapolated from TCC ObjNetPos
ARCOFFX = -6.6666700000000E-02 / TCC arc offset X
ARCOFFY = +0.0000000000000E+00 / TCC arc offset Y
CALOFFX = +0.0000000000000E+00 / TCC calibration offset X
CALOFFY = +0.0000000000000E+00 / TCC calibration offset Y
BOREOFFX= +0.0000000000000E+00 / TCC boresight offset X
BOREOFFY= +0.0000000000000E+00 / TCC boresight offset Y
AIRPRESS= +7.2888000000000E+04 / Air pressure, Pascals
HUMIDITY= +1.3000000000000E-01 / Humidity, fraction
TELAZ   = +1.0668439000000E+01 / TCC AxePos azimuth
TELALT  = +3.0615123000000E+01 / TCC AxePos altitude
TELROT  = +4.0366414000000E+01 / TCC AxePos rotator
TELFOCUS= +2.7100000000000E+02 / TCC SecFocus
ZD      = +5.9384877000000E+01 / Zenith distance
AIRMASS = +1.9636003956248E+00 / 1/cos(ZD)
CTYPE1  = 'RA---TAN'           / WCS projection
CTYPE2  = 'DEC--TAN'           / WCS projection
CRPIX1  =            506.03615 / WCS reference pixel
CRPIX2  =            565.75294 / WCS reference pixel
CRVAL1  =           267.894173 / WCS reference sky pos.
CRVAL2  =           -25.848215 / WCS reference sky pos.
CD1_1   = +7.5550943338896E-05 / WCS (1/InstScaleX)*cos(InstAng)
CD1_2   = +4.2637734975314E-08 / WCS (1/InstScaleY)*sin(InstAng)
CD2_1   = -4.2587160226021E-08 / WCS (-1/(InstScaleX)*sin(InstAng)
CD2_2   = +7.5640664513022E-05 / WCS (1/InstScaleY)*cos(InstAng)
WCSDIM  =                    2
LTM1_1  =                   1.
LTM2_2  =                   1.
WAT0_001= 'system=image'
WAT1_001= 'wtype=tan axtype=ra'
WAT2_001= 'wtype=tan axtype=dec'
NCOMBINE=                   20
IMCMB001= 'BC2_e_H2_diff.fits'
IMCMB002= '1.fits  '
COMMENT   28 blank lines
END

Bania2 header:

$ imhead CHIMPS/Bania2_downsampled_kms.fits
SIMPLE  =                    T / conforms to FITS standard
BITPIX  =                  -64 / array data type
NAXIS   =                    3 / number of array dimensions
NAXIS1  =                  550
NAXIS2  =                  590
NAXIS3  =                  131
BUNIT   = 'K       '           / Units of the primary array
DATE    = '2019-07-06T13:38:58' / file creation date (YYYY-MM-DDThh:mm:ss UT)
ORIGIN  = 'East Asian Observatory' / Origin of file
BMAJ    =      0.0041666666666
BMIN    =     0.00416666666666
BPA     =                  0.0
WCSAXES =                    3 / Number of coordinate axes
CRPIX1  =              426.798 / Pixel coordinate of reference point
CRPIX2  =              265.753 / Pixel coordinate of reference point
CRPIX3  =                65.75 / Pixel coordinate of reference point
CDELT1  =  -0.0016666666666732 / [deg] Coordinate increment at reference point
CDELT2  =   0.0016666666666677 / [deg] Coordinate increment at reference point
CDELT3  =                 -6.0 / [m/s] Coordinate increment at reference point
CUNIT1  = 'deg'                / Units of coordinate increment and value
CUNIT2  = 'deg'                / Units of coordinate increment and value
CUNIT3  = 'km s-1  '           / Units of coordinate increment and value
CTYPE1  = 'GLON-TAN'           / Galactic longitude, gnomonic projection
CTYPE2  = 'GLAT-TAN'           / Galactic latitude, gnomonic projection
CTYPE3  = 'VRAD'               / Radio velocity (linear)
CRVAL1  =                  3.0 / [deg] Coordinate value at reference point
CRVAL2  =             0.000000 / [deg] Coordinate value at reference point
CRVAL3  =     -14.900250073081 / [m/s] Coordinate value at reference point
RESTFRQ =       345795989900.0 / [Hz] Line rest frequency
MJDREF  =                  0.0 / [d] MJD of fiducial time
DATE-OBS= '2018-08-13T07:11:50.088' / ISO-8601 time of observation
MJD-OBS =       58343.29988528 / [d] MJD of observation
DATE-END= '2018-09-15T06:19:59' / ISO-8601 time at end of observation
MJD-END =      58376.263877315 / [d] MJD at end of observation
OBSGEO-X=        -5464586.7038 / [m] observatory X-coordinate
OBSGEO-Y=     -2492996.9384415 / [m] observatory Y-coordinate
OBSGEO-Z=      2150653.6634182 / [m] observatory Z-coordinate
SPECSYS = 'LSRK'               / Reference frame of spectral coordinates
SSYSOBS = 'TOPOCENT'           / Reference frame of spectral observation
VELOSYS =      12233.982413461 / [m/s] Velocity towards source
ZSOURCE =                  0.0 / Redshift of the source
SSYSSRC = 'LSRK'               / Reference frame of source redshift
COMMENT Original Unit=m / s
COMMENT Original Type=VRAD
HISTORY Written by spectral_cube v0.6.6.dev71+g89db2de on 2024/09/08-21:23:26
END

Expected behavior AFAICT, these are perfectly reasonable FITS headers with valid WCSes. Astropy's WCS recognizes them.

Platform info (please complete the following information):

Additional context The Inspector console gives these messages:

Cannot perform spatial transform between images with non-square pixels
main.8fd3acb4.js:8 Error creating spatial transform between files 6 and 0
main.8fd3acb4.js:8 Error creating spatial transform between files 7 and 0

Looking at those last messages.... is the issue just the incredibly tiny non-squareness? I'll try without that, but that is still a bug.

keflavich commented 2 months ago

OK, as often happens, the act of writing up the issue led to the "solution" (though I think it's just a workaround): the WCSes both have CD/CDELTs that differ a tiny amount. In the second case, it's only in the 14th decimal place.

I'd recommend having the 'are CDs equal?' check be a little softer - allow variation at the level of 1 part in 10^9, maybe?