[bug #58640] Error in calculation of SIP to TPV coversions

[Raul Infante-Sainz]

Follow-up Comment #2, bug #58640 (project gnuastro):

Thanks Mohammad.

1. Tarball installed without any problem and working with header only fits
file! :-)

2. I think that solved the very big/small values of some coefficients. Now I
obtain the following.

With Python:


                      / World Coordinate System (WCS)
WCSAXES =                    2 / Number of coordinate axes
CRPIX1  =        976.816238403 / Pixel coordinate of reference point
CRPIX2  =        440.521743774 / Pixel coordinate of reference point
PC1_1   =    -1.00022174065751 / Coordinate transformation matrix element
PC1_2   =    -0.00319660295795 / Coordinate transformation matrix element
PC2_1   =    -0.00235639222511 / Coordinate transformation matrix element
PC2_2   =     0.99977077772003 / Coordinate transformation matrix element
CDELT1  =  9.34302943928898E-05 / [deg] Coordinate increment at reference
point
CDELT2  =  9.35240534339602E-05 / [deg] Coordinate increment at reference
point
CUNIT1  = 'deg'                / Units of coordinate increment and value
CUNIT2  = 'deg'                / Units of coordinate increment and value
CTYPE1  = 'RA---TPV'           / TAN (gnomonic) projection + distortions
CTYPE2  = 'DEC--TPV'           / TAN (gnomonic) projection + distortions
CRVAL1  =        39.9265010846 / [deg] Coordinate value at reference point
CRVAL2  =       -8.12618217247 / [deg] Coordinate value at reference point
LONPOLE =                180.0 / [deg] Native longitude of celestial pole
LATPOLE =       -8.12618217247 / [deg] Native latitude of celestial pole
RADESYS = 'FK5'                / Equatorial coordinate system
EQUINOX =               2000.0 / [yr] Equinox of equatorial coordinates
PV1_1   =                   1.0 / TPV coefficient: x
PV1_4   =  2.74744439572126E-03 / TPV coefficient: xx
PV1_5   = -2.51914579463917E-03 / TPV coefficient: xy
PV1_6   = -4.48803400336329E-03 / TPV coefficient: yy
PV2_1   =                   1.0 / TPV coefficient: y
PV2_4   = -2.52742435899630E-03 / TPV coefficient: yy
PV2_5   =  1.75088471295910E-02 / TPV coefficient: yx
PV2_6   = -5.71014067284307E-03 / TPV coefficient: xx



With Gnuastro:


                      / World Coordinate System (WCS)
WCSAXES =                    2 / Number of coordinate axes
CRPIX1  =         976.81623840 / Pixel coordinate of reference point
CRPIX2  =         440.52174377 / Pixel coordinate of reference point
PC1_1   =    -1.00022174065751 / Coordinate transformation matrix element
PC1_2   =    -0.00319660295795 / Coordinate transformation matrix element
PC2_1   =    -0.00235639222511 / Coordinate transformation matrix element
PC2_2   =     0.99977077772003 / Coordinate transformation matrix element
CDELT1  =  9.34302943928899E-05 / [deg] Coordinate increment at reference
point
CDELT2  =  9.35240534339601E-05 / [deg] Coordinate increment at reference
point
CUNIT1  = 'deg'                / Units of coordinate increment and value
CUNIT2  = 'deg'                / Units of coordinate increment and value
CTYPE1  = 'RA---TPV'           / TAN (gnomonic) projection + distortions
CTYPE2  = 'DEC--TPV'           / TAN (gnomonic) projection + distortions
CRVAL1  =        39.9265010846 / [deg] Coordinate value at reference point
CRVAL2  =        -8.1261821725 / [deg] Coordinate value at reference point
LONPOLE =                180.0 / [deg] Native longitude of celestial pole
LATPOLE =        -8.1261821725 / [deg] Native latitude of celestial pole
RADESYS = 'FK5'                / Equatorial coordinate system
EQUINOX =               2000.0 / [yr] Equinox of equatorial coordinates
PV1_0   =   1.889113867242E-10 / TPV coefficient: 1
PV1_1   =   1.000000002193E+00 / TPV coefficient: x
PV1_2   =  -4.561985107818E-09 / TPV coefficient: y
PV1_4   =   2.710853423663E-03 / TPV coefficient: xx
PV1_5   =  -2.407209583341E-03 / TPV coefficient: xy
PV1_6   =  -4.504079860535E-03 / TPV coefficient: yy
PV2_0   =  -5.914329028462E-08 / TPV coefficient: 1
PV2_1   =   1.000001428240E+00 / TPV coefficient: y
PV2_2   =  -6.865513780250E-07 / TPV coefficient: x
PV2_4   =   2.496120304034E-03 / TPV coefficient: yy
PV2_5   =  -1.753549801538E-02 / TPV coefficient: yx
PV2_6   =   5.745550377824E-03 / TPV coefficient: xx


Now I see they are pretty similar. In some cases I think the Python script is
rounding (PV1_1, PV2_1 ~ 1) or even removing them (PV1_0, PV20 ~ 0). What do
you think? Thanks a lot, great work! :-)


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