WCSaxes show data flipped (labels are attached to wrong axes)

Minimalist WE:

from astropy.wcs import WCS
from astropy.io import fits
from astropy.visualization import simple_norm
import pylab as pl
from astropy import units as u

hdul = fits.open('https://stpubdata-jwst.stsci.edu/ero/jw02731/L3/t/jw02731-o002_t017_miri_f1800w_i2d.fits')

pl.figure(figsize=(10,10))
ww = WCS(hdul[1].header)

ax = pl.subplot(projection=ww)
ax.imshow(hdul[1].data, norm=simple_norm(hdul[1].data, max_percent=99.95))

lon = ax.coords[0]
lat = ax.coords[1]
lon.set_major_formatter('dd:mm:ss.ss')
lat.set_major_formatter('dd:mm:ss.ss')
lon.set_ticks(spacing=30. * u.arcsec)
lat.set_ticks(spacing=30. * u.arcsec)
lon.set_ticklabel(rotation=45, pad=30)

Result:

Problem: the X-axis is declination!

The header is this:

XTENSION= 'IMAGE   '           / Image extension                                
BITPIX  =                  -32 / array data type                                
NAXIS   =                    2 / number of array dimensions                     
NAXIS1  =                 3470                                                  
NAXIS2  =                 1174                                                  
PCOUNT  =                    0 / number of parameters                           
GCOUNT  =                    1 / number of groups                               
EXTNAME = 'SCI     '           / extension name                                 
MJD-BEG =    59741.12639981297 / [d] exposure start time in MJD                 
MJD-AVG =    59741.34160363826 / [d] exposure mid-point in MJD                  
MJD-END =    59741.55679824074 / [d] exposure end time in MJD                   
TDB-BEG =    59741.13163161634 / [d] TDB time of exposure start in MJD          
TDB-MID =    59741.34683091205 / [d] TDB time of exposure mid-point in MJD      
TDB-END =    59741.56202095382 / [d] TDB time of exposure end in MJD            
XPOSURE =              5994.08 / [s] Effective exposure time                    
TELAPSE =              5994.08 / [s] Total elapsed exposure time                
                                                                                
        JWST ephemeris information                                              
                                                                                
REFFRAME= 'EME2000 '           / Ephemeris reference frame                      
EPH_TYPE= 'Definitive'         / Definitive or Predicted                        
EPH_TIME=    59741.14305555556 / UTC time of position and velocity vectors in ep
JWST_X  =   -27666471.75619852 / [km] barycentric JWST X coordinate at MJD_AVG  
JWST_Y  =   -138329023.1183411 / [km] barycentric JWST Y coordinate at MJD_AVG  
JWST_Z  =   -60289095.90038356 / [km] barycentric JWST Z coordinate at MJD_AVG  
OBSGEO-X=     270741107.153853 / [m] geocentric JWST X coordinate at MJD_AVG    
OBSGEO-Y=    -1382637909.38873 / [m] geocentric JWST Y coordinate at MJD_AVG    
OBSGEO-Z=    -955370885.732361 / [m] geocentric JWST Z coordinate at MJD_AVG    
JWST_DX =    28.95847034488103 / [km/s] barycentric JWST X velocity at MJD_AVG  
JWST_DY =   -4.858839776968531 / [km/s] barycentric JWST Y velocity at MJD_AVG  
JWST_DZ =   -2.234909903693477 / [km/s] barycentric JWST Z velocity at MJD_AVG  
OBSGEODX=     125.020158763399 / [m/s] geocentric JWST X velocity at MJD_AVG    
OBSGEODY=     35.8482128539545 / [m/s] geocentric JWST Y velocity at MJD_AVG    
OBSGEODZ=    -114.373851163562 / [m/s] geocentric JWST Z velocity at MJD_AVG    
PA_APER =    116.7940399545248 / [deg] Position angle of aperture used          
VA_SCALE=   0.9999562813367563 / Velocity aberration scale factor               
BUNIT   = 'MJy/sr  '           / physical units of the array values             
                                                                                
        Photometry information                                                  
                                                                                
PHOTMJSR=   0.4943844079971313 / Flux density (MJy/steradian) producing 1 cps   
PHOTUJA2=     11.6202239773816 / Flux density (uJy/arcsec2) producing 1 cps     
PIXAR_SR= 2.84403609523084E-13 / Nominal pixel area in steradians               
PIXAR_A2=               0.0121 / Nominal pixel area in arcsec^2                 
                                                                                
        Information about the coordinates in the file                           
                                                                                
RADESYS = 'ICRS    '           / Name of the coordinate reference frame         
                                                                                
        Spacecraft pointing information                                         
                                                                                
RA_V1   =    159.3540771893557 / [deg] RA of telescope V1 axis                  
DEC_V1  =   -58.73506412600148 / [deg] Dec of telescope V1 axis                 
PA_V3   =    111.8777236761156 / [deg] Position angle of telescope V3 axis      
                                                                                
        WCS parameters                                                          
                                                                                
WCSAXES =                    2 / number of World Coordinate System axes         
CRPIX1  =    1731.103892447788 / axis 1 coordinate of the reference pixel       
CRPIX2  =    581.0376680959058 / axis 2 coordinate of the reference pixel       
CRVAL1  =     159.221073504818 / first axis value at the reference pixel        
CRVAL2  =   -58.61772542066391 / second axis value at the reference pixel       
CTYPE1  = 'RA---TAN'           / first axis coordinate type                     
CTYPE2  = 'DEC--TAN'           / second axis coordinate type                    
CUNIT1  = 'deg     '           / first axis units                               
CUNIT2  = 'deg     '           / second axis units                              
CDELT1  =  3.0808700908093E-05 / first axis increment per pixel                 
CDELT2  =  3.0808700908093E-05 / second axis increment per pixel                
PC1_1   =   0.4507846893158868 / linear transformation matrix element           
PC1_2   =   0.8926327149944592 / linear transformation matrix element           
PC2_1   =   0.8926327149944592 / linear transformation matrix element           
PC2_2   =  -0.4507846893158868 / linear transformation matrix element           
S_REGION= 'POLYGON ICRS  159.144213298 -58.657226232 159.206276111 &'           
CONTINUE  '-58.673552892 159.298755295 -58.578102372 159.236818600 &'           
CONTINUE  '-58.561820231&'                                                      
CONTINUE  '' / spatial extent of the observation                                
VELOSYS =             13087.39 / [m/s] Barycentric correction to radial velocity
EXTVER  =                    1 / extension value   

Note that the PC matrix is bigger in the 1_2 and 2_1 terms - so, the image is rotated. But, the axis labels are attached as if the image is not rotated.

Workaround: Reproject the image to a north-facing WCS. There’s nothing wrong with the underlying axes, just the labels, afaict.

[keflavich]

That works:

dec.set_ticks_position('bt')
dec.set_ticklabel_position('bt')
dec.set_axislabel_position('bt')
ra.set_ticks_position('lr')
ra.set_ticklabel_position('lr')
ra.set_axislabel_position('lr')

[astrofrog]

Yes looking at this more I think this is what we might want to use to figure out which coordinate to show preferentially on which axis. We’ll have to think about whether we are ok with this potentially changing user figures - but I think it might be ok because for cases where we would actually swap the coordinates, the default output was probably not optimal and users might have anyway manually specified where to show the labels (in which case changing the default won’t change anything). If users didn’t fix it, they might welcome the improvement.